Q&A: #IPCC wraps up its most in-depth assessment of #ClimateChange — @CarbonBrief #ActOnClimate #KeepItInTheGround

Delegates at the IPCC meeting in Interlaken, Switzerland, on 18 March 2023. Credit: IISD

Click the link to read the article on the Carbon Brief website (Aruna Chandra, Daisy Dunne, Orla Dwyer, Simon Evans, Robert McSweeney, Ayesha Tandon, and Giuliana Viglione)

The final part of the world’s most comprehensive assessment of climate change – which details the “unequivocal” role of humans, its impacts on “every region” of the world and what must be done to solve it – has now been published in full by the UN’s Intergovernmental Panel on Climate Change (IPCC).

The synthesis report is the last in the IPCC’s sixth assessment cycle, which has involved 700 scientists in 91 countries. Overall, the full cycle of reports has taken eight years to complete.

The report sets out in the clearest and most evidenced detail yet how humans are responsible for the 1.1C of temperature rise seen since the start of the industrial era.

It also shows how the impacts of this level of warming are already deadly and disproportionately heaped upon the world’s most vulnerable people.

The report notes that policies in place by the end of 2021 – the cut-off date for evidence cited in the assessment – would likely see temperatures exceed 1.5C this century and reach around 3.2C by 2100.

In many parts of the world, humans and ecosystems will be unable to adapt to this amount of warming, it says. And the losses and damages will “escalate with every increment” of global temperature rise.

But it also lays out how governments can still take action to avoid the worst of climate change, with the rest of this decade being crucial for deciding impacts for the rest of the century. The report says:

“There is a rapidly closing window of opportunity to secure a liveable and sustainable future for all…The choices and actions implemented in this decade will have impacts now and for thousands of years.”

The report shows that many options for tackling climate change – from wind and solar power to tackling food waste and greening cities – are already cost effective, enjoy public support and would come with co-benefits for human health and nature.

At a press briefing, leading climate scientist and IPCC author Prof Friederike Otto said the report highlights “not only the urgency of the problem and the gravity of it, but also lots of reasons for hope – because we still have the time to act and we have everything we need”.

Carbon Brief’s team of journalists has delved through each page of the IPCC’s AR6 full synthesis report to produce a digestible summary of the key findings and graphics. 

1. What is this report? 

The synthesis report is the final part of the IPCC’s sixth assessment cycle. It “integrates” the main findings of the three working group reports, which have been published over the last 18 months or so:

The synthesis also takes into account the three shorter “special reports” that the IPCC has published during the sixth assessment cycle:

As the “mandate” was to produce a synthesis of existing material, “there is nothing that is in there that is not in the underlying reports”, author Prof Fredi Otto – a senior lecturer at the Grantham Institute for Climate Change and the Environment at Imperial College London – told a press briefing. This means that the report does not include any research or emissions pledges issued after the cut-off date for the WG3 assessment – which was 11 October 2021, several weeks before the COP26 climate summit in Glasgow.

The synthesis report is much shorter than the full assessment reports. The combined length of the “summary for policymakers” (SPM) – a short, non-technical synopsis – and the underlying report clocks in at 122 pages. This is longer than the 42.5 pages that were planned (pdf), but a fraction of the assessment reports that can top 3,000 pages. As with the assessment reports, the synthesis report has been through several rounds of review by experts and governments.

The report’s SPM was signed off via a line-by-line approval session involving authors and government delegates last week in Switzerland.

However, unlike the assessment reports, the session also approved the underlying full report “section by section”. It was also the IPCC’s first approval session since the Covid-19 pandemic that was held in person.

The approval process was scheduled to be completed on Friday 17 March, but overran – despite multiple “night sessions” and “round-the-clock deliberations”. The SPM was finally approved on the morning of Sunday 19 March in a “sparsely attended room”, as many developing country delegates had already left the venue, Third World Network reported. “People who have to contribute have left the meeting,” said India’s representatives in the early hours before the closing plenary.  

 Once the SPM was approved, there was then a “huge moment of panic” around whether “it would at all be possible to do the approval of the long report”, Otto said:

“We all almost died of adrenaline poisoning during [Sunday], but then it was approved quite straightforwardly.”

(The Earth Negotiations Bulletin has published a summary of the discussions during the approval session. This is referenced frequently in this article.)

The synthesis report shares the IPCC’s “calibrated language” that the assessment reports use to communicate levels of certainty behind the statements it includes. 

The findings are given “as statements of fact or associated with an assessed level of confidence”, based on scientific understanding. The language indicates the “underlying evidence and agreement”, the report explains:

“A level of confidence is expressed using five qualifiers: very low, low, medium, high and very high, and typeset in italics, for example, medium confidence

“The following terms have been used to indicate the assessed likelihood of an outcome or result: virtually certain 99-100% probability; very likely 90-100%; likely 66-100%; more likely than not >50-100%; about as likely as not 33-66%; unlikely 0-33%; very unlikely 0—10%; and exceptionally unlikely 0-1%. Additional terms (extremely likely 95-100%; more likely than not >50-100%; and extremely unlikely 0-5%) are also used when appropriate.”

The synthesis includes projections based on the latest generation of global climate models, produced as part of the sixth Coupled Model Intercomparison Project (CMIP6) for the AR6 cycle. However, it also brings together different approaches for how future pathways were considered in the assessment reports.

The WG1 report “assessed the climate response to five illustrative scenarios based on Shared Socioeconomic Pathways (SSPs) that cover the range of possible future development of anthropogenic drivers of climate change found in the literature”, the synthesis explains:

“The high and very high GHG emissions scenarios (SSP3-7.0 and SSP5-8.5) have CO2 emissions that roughly double from current levels by 2100 and 2050, respectively. The intermediate GHG emissions scenario (SSP2-4.5) has CO2 emissions remaining around current levels until the middle of the century. The very low and low GHG emissions scenarios (SSP1-1.9 and SSP1-2.6) have CO2 emissions declining to net-zero around 2050 and 2070, respectively, followed by varying levels of net-negative CO2 emissions.”

In contrast, the WG3 report assessed “a large number of global modelled emissions pathways…of which 1,202 pathways were categorised based on their projected global warming over the 21st century, with categories ranging from pathways that limit warming to 1.5C with more than 50% likelihood with no or limited overshoot (C1) to pathways that exceed 4C (C8)”.

The table below, taken from the synthesis report, shows how these pathways relate to the SSPs and their predecessors, the Representative Concentration Pathways (RCPs).

Description and relationship of scenarios and modelled pathways considered across AR6 working group reports. Source: IPCC (2023) Box SPM.1, Table 1

The synthesis report is the final product of the IPCC’s sixth assessment cycle. Its delay from the planned publication in September last year for “management reasons” – and the lack of transparency surrounding these issues – resulted in “unusually blunt statements of discontent from governments” about the IPCC’s impact and credibility, the Earth Negotiations Bulletin reported at the time. 

Nonetheless, governments agreed at a September meeting that the IPCC’s seventh assessment cycle (AR7) will begin in July this year and will have a length of between five and seven years. The end of AR6 and the start of AR7 will see the election of a new IPCC leadership team – including chair, vice-chairs and working group co-chairs. The first full assessment reports of AR7 would likely not be expected until 2027 or 2028.

The SPM says with high confidence that human activities have “unequivocally caused global warming”.

2. How is the Earth’s climate changing?

This statement – first made in the IPCC’s WG1 report – is the strongest wording to date about the role of human activities on observed warming from any IPCC assessment cycle. 

Overall, the report says that global surface temperature in 2011-20 averaged at 1.09C above 1850-1900 levels – with a 1.59C rise seen over land and a 0.88C rise over the ocean. It adds, with high confidence, that “global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years”.

According to the Earth Negotiations Bulletin, delegates “disagreed on how much information to include” in the SPM sub-paragraph on global surface temperature increases. The bulletin outlines the lengthy discussion needed to finalise this section of the text – including decisions on whether to use the “more precise” 1.09C or the rounded 1.1C figure and warnings that the addition of extra sentences “overloaded the sub-paragraph with numbers and diluted the message”.

The SPM also discusses the observed changes and impacts of climate change to date. It makes the following statement with high confidence:

“Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred. Human-caused climate change is already affecting many weather and climate extremes in every region across the globe. This has led to widespread adverse impacts and related losses and damages to nature and people.”

It says that global average sea levels increased by 0.2 metres between 1901 and 2018. Sea level rise accelerated over this time, from a rate of 1.3mm per year over 1901-71 to 2.7mm per year over 2006-18, it adds.

The SPM for the AR6 synthesis report is longer than its AR5 counterpart (pdf) and contains more numbers in its section on observed changes in the climate system.

For example, the AR5 report does not quantify the rate of acceleration of sea level rise, instead saying that “the rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia (high confidence)”.

Meanwhile, the SPM says human influence has likely increased the chance of “compound” extreme events since the 1950s, including increases in the frequency of concurrent heatwaves and droughts.

The SPM has very high confidence that “increases in extreme heat events have resulted in human mortality and morbidity” in all regions. It adds that extreme temperatures also cause mental health challenges, trauma and the loss of livelihoods and culture. The report also has high confidence that climate change is “contributing to humanitarian crises where climate hazards interact with high vulnerability”.

India in 2022 faced a prolonged heatwave, with temperatures exceeding 42°C in numerous cities across the country. This came just weeks after India recorded its hottest March since the country’s meteorological department began its records over 120 years ago. This image, produced using data from the Copernicus Sentinel-3 mission, shows the land surface temperature across most of the nation. According to the India Meteorological Department, maximum air temperatures reached 43-46°C over most parts of Rajasthan, Vidarbha, Madhya Pradesh and East Uttar Pradesh; in many parts over Gujarat, interior Odisha; and in some parts of Madhya Maharashtra on 28 April. Forecasters warned that heatwave conditions are expected to continue until 2 May. Experts at the Indian Institute of Technology’s Water and Climate Lab stated that, in recent years, the number of Indian states hit by heatwaves has increased, as extreme temperatures become more frequent. Owing to the absence of cloud cover on 29 April (10:30 local time), the Sentinel-3 mission was able to obtain an accurate measurement of the land surface temperature of the ground, which exceeded 60°C in several areas. The data shows that surface temperature in Jaipur and Ahmedabad reached 47°C, while the hottest temperatures recorded are southeast and southwest of Ahmedabad (visible in deep red) with maximum land surface temperatures of around 65°C. The map was generated by using the mission’s Sea and Land Surface Temperature Radiometer instrument. While weather forecasts use predicted air temperatures, this satellite instrument measures the real amount of energy radiating from Earth. Therefore, the map shows the actual temperature of the land’s surface pictured here, which is usually significantly hotter than air temperatures. Sentinel-3 can monitor wildfires, map the way the land is used, provide indices of vegetation state, as well as measure the temperature, colour and height of the sea surface. For more information on the Copernicus Sentinel-3 mission, click here. By Contains modified Copernicus Sentinel data 2022, Attribution, https://commons.wikimedia.org/w/index.php?curid=117497147

Elsewhere, the report has high confidence that animal and human diseases including zoonoses – infections that pass between animals and people – “are emerging in new areas” and very high confidence that “the occurrence of climate-related food-borne and water-borne diseases has increased”.

The SPM warns that climate and weather extremes are “increasingly driving displacement in Africa, Asia, North America (high confidence), and Central and South America (medium confidence), with small island states in the Caribbean and South Pacific being disproportionately affected relative to their small population size (high confidence)”.

The authors write that hot extremes have intensified in cities and that they have high confidence that the observed adverse impacts are “concentrated amongst economically and socially marginalised urban residents”.

The report elaborates, saying it has high confidence that “urban infrastructure including transportation, water, sanitation and energy systems have been compromised by extreme and slow-onset events, with resulting economic losses, disruptions of services and impacts to well-being”.

The table below shows observed changes in the climate and their attribution to human influence. Darker colours indicate a higher confidence in the changes and their human influence. Notably, the table lists “warming of the global climate system since pre-industrial times” as a “fact”.

Observed changes in the climate and their attribution to human influence. Darker colours indicate a higher confidence in the findings. Source: IPCC (2023) Table 2.1

The report has high confidence that climate change has hindered efforts to meet the Sustainable Development Goals by reducing food security, changing rainfall patterns, melting bodies of ice such as glaciers and driving more intense and frequent extreme weather events.

For example, the report says that “increasing weather and climate extreme events have exposed millions of people to acute food insecurity and reduced water security”. (For more on how climate change is affecting extreme weather, see Carbon Brief’s coverage of the IPCC’s WG1 report.)

The report also says that “substantial damages, and increasingly irreversible losses” have already been sustained. For example, it has very high confidence that approximately half of the species assessed globally have shifted polewards or to higher elevations. It has medium confidence that impacts on some ecosystems are “approaching irreversibility” – for example the impacts of hydrological changes resulting from glacial retreat.

The report also has high confidence that “economic impacts attributable to climate change are increasingly affecting peoples’ livelihoods and are causing economic and societal impacts across national boundaries”. 

3. How are human-caused emissions driving global warming?

The report states as fact – that is, with no calibrated language – that “human activities, principally through emissions of greenhouse gases, have unequivocally caused global warming”. 

In other words, the report states, “human-caused climate change is a consequence of more than a century of net GHG emissions from energy use, land-use and land use change, lifestyle and patterns of consumption, and production”.

Specifically, the report explains that humans have contributed to 1.07C of the observed warming between 1850-1900 and 2010-19, with a likely range of 0.8-1.3C. As the total observed warming over the same period is 1.06C, this means that humans have caused 100% of the long-term global warming to date.

This conclusion is in line with the synthesis report (pdf) of the IPCC’s fifth assessment report (AR5), published in 2014, which said:

“The best estimate of the human-induced contribution to warming is similar to the observed warming over [1951-2010].“

That the influence of human activity is marginally larger than the observed temperature rise reflects the mix of impacts that an industrialised society is having. The warming impact of the GHGs that human activity has produced is likely to be in the range of 1.0-2.0C. But then there is also the cooling influence of other “human drivers (principally aerosols)”, the report notes. 

Aerosols include tiny particles – such as soot – that are produced from cars, factories and power stations. They tend to have an overall cooling effect on the Earth’s climate by scattering incoming sunlight and stimulating clouds to form. These human drivers could have contributed to a cooling of 0.0-0.8C, the IPCC says. 

The net cooling effect of human-caused aerosols “peaked in the late 20th century”, the report notes with high confidence.

Natural influences on the climate had only a small influence on the long-term trend in global temperature, the reports says, with fluctuations in the sun and volcanic activity causing between -0.1C and 0.1C of temperature change and other natural variability causing between -0.2C and 0.2C.

The increase in concentrations of GHGs in the atmosphere since around 1750 “are unequivocally caused by GHG emissions from human activities over this period”, the IPCC says:

“In 2019, atmospheric CO2 concentrations (410 parts per million) were higher than at any time in at least 2m years (high confidence), and concentrations of methane (1866 parts per billion) and nitrous oxide (332 parts per billion) were higher than at any time in at least 800,000 years (very high confidence).”

The figure below shows “the causal chain from emissions to resulting warming of the climate system”. The bottom panel shows the increase in GHGs over 1850-2019, the middle panel shows the resulting rise in atmospheric greenhouse gas emissions, the top left panel shows the change in global surface temperature since 1850 and the top right panel separates the warming out into its different contributing factors.

The causal chain from emissions to resulting warming of the climate system. Panel (a) shows the increase in GHGs over 1850-2019. Panel (b) shows the resulting rise in atmospheric greenhouse gas emissions. Panel (c) shows the change in global surface temperature since 1850. Panel (d) separates the warming out into its different contributing factors. Source: IPCC (2023) Figure 2.1

The report says with high confidence that “land and ocean sinks have taken up a near-constant proportion (globally about 56% per year) of CO2 emissions from human activities over the past six decades”. However, looking to the future, it adds: 

“In scenarios with increasing CO2 emissions, the land and ocean carbon sinks are projected to be less effective at slowing the accumulation of CO2 in the atmosphere (high confidence). 

“While natural land and ocean carbon sinks are projected to take up, in absolute terms, a progressively larger amount of CO2 under higher compared to lower CO2 emissions scenarios, they become less effective, that is, the proportion of emissions taken up by land and ocean decreases with increasing cumulative net CO2 emissions (high confidence).”

In 2019, global net emissions of GHGs clocked in at 59bn tonnes of CO2 equivalent (GtCO2e), the report says. This is 12% higher than in 2010 and 54% higher than in 1990, with “the largest share and growth in gross GHG emissions occurring in CO2 from fossil fuels combustion and industrial processes followed by methane”. 

The report says, with high confidence, that GHG emissions since 2010 have increased “across all major sectors”. It continues:

“In 2019, approximately 34% (20GtCO2e) of net global GHG emissions came from the energy sector, 24% (14GtCO2e) from industry, 22% (13GtCO2e) from AFOLU, 15% (8.7GtCO2e) from transport and 6% (3.3GtCO2e) from buildings.”

However, although average annual GHG emissions between 2010 and 2019 were “higher than in any previous decade”, the rate of growth during this period (1.3% per year) “was lower than that between 2000 and 2009” (2.1% per year), the report notes. This sentence – which also featured in the WG3 report – was added during the approval session at the request of China, the Earth Negotiations Bulletin reported.

Historical contributions to global GHGs “vary substantially across regions” and “continue to differ widely”, the authors note. 

In 2019, around 35% of the global population were in countries emitting more than nine tonnes of CO2e per capita – excluding CO2 emissions from land use, land-use change and forestry (LULUCF), the report says.

In contrast, 41% were in countries emitting less than three tonnes of CO2e. It adds that least developed countries (LDCs) and small island developing states (SIDS), in particular, have much lower per-capita emissions (1.7 and 4.6 tonnes of CO2e, respectively) than the global average (6.9 tonnes), excluding CO2 from LULUCF.

Perhaps most starkly, the authors note with high confidence:

“The 10% of households with the highest per-capita emissions contribute 34-45% of global consumption-based household GHG emissions, while the bottom 50% contribute 13-15%.”

The regional variations in emissions are illustrated by the figure below, which shows historical contributions (top-left), per capita emissions in 2019 (top-right) and global emissions since 1990 broken down by emissions (bottom). (For more on historical responsibility for emissions, see Carbon Brief’s analysis from 2021.)

During the approval session, France – supported by around 15 other countries, including the US and Canada – requested that this figure was elevated into the SPM “to provide a clear and necessary narrative about the causes of warming”, the Earth Negotiations Bulletin reported. However, Saudi Arabia, India and China opposed the move and a subsequent huddle was “unable to reach consensus”.

Regional contribution to global GHG emissions. Panel (a) shows the share of historical cumulative net anthropogenic CO2 emissions per region from 1850 to 2019 in GtCO2. Panel (b) shows the distribution of regional per-capita GHG emissions in tonnes CO2e by region in 2019. Both (a) and (b) are separated out by emissions category. Panel (c) shows global net human-caused GHG emissions by region (in GtCO2e per year) for 1990-2019. Percentage values refer to the contribution of each region to total GHG emissions in each respective time period. (The single-year peak of emissions in 1997 was due to a forest and peat fire event in south-east Asia.) Source: IPCC (2023) Figure 2.2

4. How much hotter will the world get this century?

The world will continue to get hotter “in the near term (2021-40)”, the report says, “in nearly all considered scenarios and pathways” for greenhouse gas emissions.

Crucially, however, there is a choice over how hot it gets by the end of the century. As the synthesis report explains: “Future warming will be driven by future emissions.”

The amount of warming this century largely depends on the amount of greenhouse gases that humans release into the atmosphere in the future “with cumulative net CO2 dominating”.

In order to stop global warming, the report says, CO2 emissions are, therefore, “require[d]” to reach net-zero. (See: What is needed to stop climate change?)

The report looks at a range of plausible futures, known as the shared socioeconomic pathways (SSPs), spanning very low to very high emissions. (See: What is this report?)

If emissions are very low (SSP1-1.9), then warming is expected to temporarily “overshoot” 1.5C by “no more than 0.1C” before returning to 1.4C in 2100, the report says.

If emissions are very high (SSP5-8.5), warming could reach 4.4C in 2100. (See below for more on what it would take for the world to follow these different emissions pathways.)

Notably, there is less uncertainty in these projections than there was in AR5. This is because the IPCC has narrowed the range of “climate sensitivity”, using observations of recorded warming to date and improved understanding of clouds.

The alternative emissions futures are shown in the figure below, which illustrates the 1.1C of warming to date and potential increases to 2100 in the style of the famous “climate stripes”.

The figure also illustrates the warming that would take place during the lifetimes of three representative generations born in 1950, 1980 and 2020.

Observed (1900-2020) and projected (2021-2100) warming relative to pre-industrial temperatures (1850-1900). Projections relate to very low emissions (SSP1-1.9), low emissions (SSP1-2.6), intermediate emissions (SSP2-4.5), high emissions (SSP3-7.0) and very high emissions (SSP5-8.5). Temperatures are colour-coded from the pre-industrial average (blue-grey) through to current warming of 1.1C (orange) and potentially more than 4C by 2100 (purple). Source: IPCC (2023) Figure SPM.1

While limiting warming in line with global targets would require “deep and rapid, and, in most cases, immediate greenhouse gas emissions reductions in all sectors this decade”, these efforts would not be felt for some time. The SPM explains with high confidence:

“Continued greenhouse gas emissions will lead to increasing warming…Deep, rapid and sustained reductions in greenhouse gas emissions would lead to a discernible slowdown in global warming within around two decades.”

This delay means that global temperatures are more likely than not to reach 1.5C during 2021-40, the report says, even if emissions are very low.

The report does not give specific “exceedance” years that breach 1.5C for each emissions pathway. (The 1.5C limit of the Paris Agreement relates to long-term averages, rather than warming in a single year.)

The SPM explains that for very low, low, intermediate and high emissions, “the midpoint of the first 20-year running average period during which [warming] reaches 1.5C lies in the first half of the 2030s”. If emissions are very high, it would be in “the late 2020s”.

Similarly, the report says warming will exceed 2C this century “unless deep reductions in CO2 and other GHG emissions occur in the coming decades”.

At the other end of the spectrum, it has “become less likely” that the world will match the very high emissions scenario (SSP5-8.5), where warming exceeds 4C this century.

The report says, with medium confidence, that emissions could only reach such high levels if there is “a reversal of current technology and/or mitigation policy trends”.

However, it says 4C of warming is possible with lower emissions, if carbon cycle feedbacks or climate sensitivity are larger than thought. It explains in a footnote to the SPM:

“Very high emissions scenarios have become less likely, but cannot be ruled out. Warming levels >4C may result from very high emissions scenarios, but can also occur from lower emission scenarios if climate sensitivity or carbon cycle feedbacks are higher than the best estimate.”

In addition to the path of greenhouse gas emissions, changing emissions of “short-lived climate forcers” (SLCFs) can also add to near- and long-term warming, the report says with high confidence. SLCFs include methane, aerosols and ozone precursors, it explains.

There have been concerns that efforts to cut greenhouse gas emissions could also reduce output of cooling aerosols, “unmasking” additional warming. The report plays down this risk:

“Simultaneous stringent climate change mitigation and air pollution control policies limit this additional warming and lead to strong benefits for air quality (high confidence).”

5. What are the potential impacts at different warming levels?

With every extra bit of global warming, extremes facing the world will become larger, the report says.

The Water Cycle. Credit: USGS

For example, it says with high confidence that continued climate change will further intensify the global water cycle, driving changes to monsoons and to very wet and very dry weather.

As temperatures rise, natural land and ocean carbon sinks will be less able to absorb emissions – worsening warming further, the report says with high confidence.

Other changes to expect include further reductions in “almost all” the world’s ice systems, from glaciers to sea ice (high confidence), further global sea level rise (virtually certain), and increasing acidity and decreasing oxygen availability in the oceans (virtually certain).

Every world region will experience more climate impacts with every bit of further warming, the report says. 

Compound heatwave and drought extremes are expected to become more frequent in many regions, the report says with high confidence. 

Nuisance flooding.

Extreme sea level events that currently occur once in every 100 years are expected to take place at least annually in more than half all measurable locations by 2100, under any future emissions scenario, it says with high confidence. (Extreme sea level events include storm surges and flooding.)

Other projected changes include the intensification of tropical storms (medium confidence) and increases in fire weather (high confidence), according to the report.

It says that the natural variability of the Earth’s climate will continue to act alongside climate change, sometimes worsening and sometimes masking its effects.

The graphic below, from the report’s SPM, illustrates some of the regional impacts of climate change at 1.5C, 2C, 3C and 4C of global warming. (Current policies from governments have the world on track for around 2.7C of warming.)

A selection of regional climate impacts at 1.5C, 2C, 3C and 4C of global warming. [The world is currently on track for 2.7C]. Source: IPCC (2023) Figure SPM.2

In the near term, every world region is expected to face further increases in climate hazards – with rising risk for humans and ecosystems (very high confidence), the report says.

Risks expected to increase in the near-term include heat-related deaths (high confidence), food-, water- and vector-borne diseases (high confidence), poor mental health (very high confidence), flooding in coastal and low-lying cities (high confidence) and a decrease in food production in some regions (high confidence).

At 1.5C, risks will increase for “health, livelihoods, food security, water supply, human security and economic growth”, the report says. At this level of global warming, many low-elevation and small glaciers around the world would lose most of their mass or disappear, the report says with high confidence. Coral reefs are expected to decline by a further 70–90%, it adds with high confidence.

At 2C, risks associated with extreme weather events will transition to “very high”, the report says with medium confidence. At this level of warming, changes in food availability and diet quality could increase nutrition-related diseases and undernourishment for up to “hundreds of millions of people”, particularly among low-income households in sub-Saharan Africa, south Asia and central America, the report says with high confidence.

At 3C, “risks in many sectors and regions reach high or very high levels, implying widespread systemic impacts”, the report says. The number of endemic species in biodiversity hotspots at a very high risk of extinction is expected to be 10 times higher than at 1.5C, it says with medium confidence.

At 4C and above, around half of tropical marine species could face local extinction, the report says with medium confidence. Around four billion people could face water scarcity, it says with medium confidence. It adds that the global area burned by wildfires could increase by 50-70% (medium confidence).

The graphic below, from the report’s SPM, illustrates the risks facing Earth’s species (a) and human health risk from extreme heat-humidity (b) under different levels of global warming. 

It shows that, at temperatures above 2C, some regions will see all of their wildlife exposed to dangerous temperatures, assuming the species do not relocate to somewhere else. 

It also shows that, above 2C, some people will live in regions where temperature and humidity conditions are deadly every day of the year. 

Risks to species and humans at various levels of global warming. Source: IPCC (2023) SPM.3a and b

The risks identified in this report are larger at lower levels at warming, when compared to the IPCC’s last assessment in 2014.

This is because of new evidence from climate extremes already recorded, improved scientific understanding, new knowledge on how some humans and species are more vulnerable than others and a better grasp of the limits to adaptation, the report says with high confidence.

Because of “unavoidable” sea level rise, risks for coastal ecosystems, people and infrastructure will continue to increase beyond 2100, it adds with high confidence.

As climate change worsens, risks “will become increasingly complex and more difficult to manage”, the report says.

Climate change is likely to compound other societal issues, it says. For example, food shortages driven by warming are projected to interact with other factors, such as conflicts, pandemics and competition over land, the report says with high confidence.

Most pathways for how the world can meet its ambitious 1.5C temperature involve a period of “overshoot” where temperatures exceed this level of warming temporarily before dropping back down.

During this period of overshoot, the world would see “adverse impacts” that may worsen climate change, such as increased wildfires, mass mortality of ecosystems and permafrost thawing, the report says with medium confidence.

The report adds that solar geoengineering – methods for reflecting away sunlight to reduce temperature rise – has the “potential to offset warming within one or two decades and ameliorate some climate hazards”, but could also “introduce a widespread range of new risks to people and ecosystems” and “would not restore climate to a previous state”.

6. What are the risks of abrupt and irreversible change?

The report warns that continued emissions of GHGs will “further affect all major climate system components and many changes will be irreversible on centennial to millennial timescales”.

While “many changes in the climate system” will become larger “in direct relation to increasing global warming”, the likelihood of “abrupt and/or irreversible outcomes increases with higher global warming levels”, the report says with high confidence. For example, it says:

“As warming levels increase, so do the risks of species extinction or irreversible loss of biodiversity in ecosystems such as forests (medium confidence), coral reefs (very high confidence) and in Arctic regions (high confidence).”

The impacts of warming on some ecosystems are already “approaching irreversibility”, the report says, “such as the impacts of hydrological changes resulting from the retreat of glaciers, or the changes in some mountain (medium confidence) and Arctic ecosystems driven by permafrost thaw (high confidence)”.

Abrupt and irreversible changes can include those “triggered when tipping points are reached”, the report says:

“Risks associated with large-scale singular events or tipping points, such as ice sheet instability or ecosystem loss from tropical forests, transition to high risk between 1.5C-2.5C (medium confidence) and to very high risk between 2.5C-4C (low confidence).”

(See Carbon Brief’s explainer for more on tipping points.) 

The report has high confidence that “the probability of low-likelihood outcomes associated with potentially very large impacts increases with higher global warming levels”. The impact of these abrupt changes would be dramatic.

Citing an example of the Atlantic Meridional Overturning Circulation (AMOC), a major system of currents in the Atlantic Ocean that brings warm water up to Europe from the tropics and beyond, the report says:

“[AMOC] is very likely to weaken over the 21st century for all considered scenarios (high confidence), however an abrupt collapse is not expected before 2100 (medium confidence). If such a low probability event were to occur, it would very likely cause abrupt shifts in regional weather patterns and water cycle, such as a southward shift in the tropical rain belt, and large impacts on ecosystems and human activities.”

For comparison, the AR5 synthesis report also concluded that a weakening of AMOC was very likely, but said that an abrupt transition or collapse in the 21st century was very unlikely.

The report notes that “low-likelihood, high-impact outcomes could occur at regional scales even for global warming within the very likely assessed range for a given GHG emissions scenario”. 

The report has a particularly stark assessment on the projected impacts of global warming on the ocean. The authors warn, with high confidence, that sea level rise is “unavoidable for centuries to millennia due to continuing deep ocean warming and ice sheet melt”. And levels will “remain elevated for thousands of years”.

While the authors are virtually certain that sea level rise will continue through this century, “the magnitude, the rate, the timing of threshold exceedances, and the long-term commitment of sea level rise depend on emissions, with higher emissions leading to greater and faster rates of sea level rise”.

Over the next 2,000 years, global average sea level “will rise by about 2-3 metres if warming is limited to 1.5C and 2-6 m if limited to 2C”, the report says, with low confidence.

Warming beyond 2C could put the Earth’s massive ice sheets at risk, the report says:

“At sustained warming levels between 2C and 3C, the Greenland and West Antarctic ice sheets will be lost almost completely and irreversibly over multiple millennia (limited evidence).”

These projections of sea level rise across thousands of years are “consistent with reconstructed levels during past warm climate periods”, the report notes.

For example, it says with medium confidence, “global mean sea level was very likely 5-25 metres higher than today roughly 3m years ago, when global temperatures were 2.5-4C higher than 1850-1900”.

In addition to rising sea levels, the authors say it is virtually certain that ocean acidification – where seawater becomes less alkaline – will continue throughout this century. And they have high confidence that deoxygenation – the decline in oxygen levels in the ocean – will too.

The report also cautions that the amount of warming – and the impact it would have – could be more severe than projected.

For example, it says, “warming substantially above the assessed very likely range for a given scenario cannot be ruled out, and there is high confidence this would lead to regional changes greater than assessed in many aspects of the climate system”.

On sea levels, the authors add:

“Global mean sea level rise above the likely range – approaching two metres by 2100 and in excess of 15 metres by 2300 under a very high GHG emissions scenario (SSP5-8.5) (low confidence) – cannot be ruled out due to deep uncertainty in ice-sheet processes and would have severe impacts on populations in low elevation coastal zones.”

7. What does the report say on loss and damage?

For the first time ever, the term “loss and damage” is mentioned in an IPCC synthesis report. This reflects its prominence in the 1.5C special report and WG2 report during the sixth assessment cycle.

The report explains the formal recognition of loss and damage via the Warsaw Mechanism on Loss and Damage and the Paris Agreement. 

It acknowledges that there has been an “improved understanding” of what constitutes economic and non-economic losses and damages. In turn, this has served to inform climate policy as well as highlight governance, financial and institutional gaps in how it is being addressed. 

The AR6 synthesis report mentions the formal recognition of “loss and damage”. Source: IPCC (2023) Full report p18

After this single mention, the report discusses “losses and damages” more broadly. These, it defines in a footnote in the SPM, are the “adverse observed impacts and/or projected risks and can be economic and/or non-economic”.

Including loss and damage in the IPCC’s assessments has been a fraught process. The use of two separate terms separates the scientific “losses and damages” from the political debate of “loss and damage” under the UNFCCC, even as impacted countries hope to connect the two.

In the plenary discussions, Grenada – supported by ​​Senegal, Antigua and Barbuda, Timor Leste, Kenya and Tanzania – wanted vulnerable countries to be referenced and the differences between the two terms explicitly clarified, given that “the distinction is often confusing to people outside of the IPCC”. The US, meanwhile, supported putting a definition in the footnote. 

On the impacts of climate change, the report recognises and reviews “strengthened” evidence of heatwaves, extreme rainfall, droughts and tropical cyclones, plus their attribution to human influence, since the last synthesis report.

In all regions, extreme heat events have resulted in human mortality and morbidity, it says with very high confidence, while climate-related food-borne and water-borne diseases have increased. Climate change is also contributing to humanitarian crises “where climate hazards interact with high vulnerability”, the report states with high confidence. 

Climate change has caused “substantial damages, and increasingly irreversible losses” in land-based, freshwater, coastal, ocean and open ecosystems, as well as in glaciers and continental ice sheets, the report’s summary says with high confidence.

The A2 headline statement from the SPM that authors “spent hours crafting” to reflect vulnerability and impacts on human and natural systems. IPCC (2023) SPM p5

The widespread “losses and damages to nature and people” are unequally distributed across systems, regions and sectors”, says the report’s summary, pointing to both economic and non-economic losses. 

Sectors such as agriculture, forestry, fishery, energy, and tourism that are “climate exposed” have experienced economic damages from climate change, the report states with high confidence. 

Across the world, non-economic loss and damage impacts, such as mental health challenges, were associated with trauma from extreme weather events and loss of livelihoods and culture. (According to the Earth Negotiations Bulletin, India requested that mental health not be included in these impacts, which Finland opposed.)

The report says with high confidence that “vulnerable communities who have historically contributed the least to current climate change are disproportionately affected”.

For example, fatalities from floods, droughts and storms were 15 times higher in highly vulnerable regions between 2010 to 2020, compared to regions with very low vulnerability, it states with high confidence.

In urban areas, losses and damages are “concentrated” in communities of economically and socially marginalised residents, the report notes.

The figure below shows observed impacts on human systems and ecosystems attributed to climate change at global and regional levels, along with confidence in their attribution to climate change.

Observed and widespread impacts and related losses and damages attributed to climate change. Mental health and displacement impacts are limited to only regions assessed. Confidence levels reflect attribution studies so far. Source: IPCC (2023), Figure SPM1a

The report states with very high confidence that “losses and damages escalate with every increment of global warming”.

These will be higher at 1.5C and even higher at 2C, the report’s summary states. Compared to AR5, “global aggregated risk levels” will be high to very high even at lower warming levels, owing to an improved understanding of exposure, vulnerability and recent evidence, including “limits to adaptation”. Climatic and non-climatic risks will increasingly interact, leading to “compound and cascading risks” that are difficult to manage.

However, near-term climate actions that rein in global warming to “close to 1.5C” could “substantially reduce” losses and damages to humans and ecosystems. Still, even these actions “cannot eliminate them all”, the report notes.

Overall, the magnitude and rate of future losses and damages “depend strongly” on near-term mitigation and adaptation actions, the report says with very high confidence

Without both, “losses and damages will continue to disproportionately affect the poorest and most vulnerable”, the report says, adding that “accelerated financial support for developing countries from developed countries and other sources is a critical enabler for mitigation action”. (See: Why is finance an ‘enabler’ and ‘barrier’ for climate action?)

Delaying mitigation will only increase warming, which could derail the effectiveness of adaptation options, it says with high confidence, leading to more climate risks and related losses and damages.

However, the report and its summary warn with high confidence that “adaptation does not prevent all losses and damages”. The authors point out with high confidence that some ecosystems, sectors and regions have already hit limits to how much they can adapt to climate impacts. In some cases, adaptive actions are unfeasible – that is, they have “hard limits” – for certain natural systems or are simply not an option because of socioeconomic or technological barriers – known as “soft limits” – leading to unavoidable loss and damage impacts. 

“One of the new messages in this report is that it effectively busts the myth of endless adaptation,” said report author Dr Aditi Mukherji, director at the Consultative Group on International Agricultural Research (CGIAR), speaking at a press conference.

8. Why is climate action currently ‘falling short’?

Current pledges for how countries will cut emissions by 2030 make it likely that global warming will exceed 1.5C this century and will make it harder to limit temperatures to 2C, according to one of the headline findings of the report.

The establishment of the Paris Agreement – the landmark climate deal reached in 2015 – has led to more target-setting and “enhanced transparency” for climate action, the report says with medium confidence.

At the same time, there has been “rising public awareness” about climate change and an “increasing diversity” of people taking action. These efforts “have overall helped accelerate political commitment and global efforts to address climate change”, the report says, adding:

“In some instances, public discourses of media and organised counter movements have impeded climate action, exacerbating helplessness and disinformation and fuelling polarisation, with negative implications for climate action (medium confidence).”

It says with high confidence that many rules and economic tools for tackling emissions have been “deployed successfully” – leading to enhanced energy efficiency, less deforestation and more low-carbon technologies in many countries. This has in some cases lowered emissions.

By 2020, laws for reducing emissions were in place in 56 countries – covering 53% of global emissions, the report says.

At least 18 countries have seen their production and consumption emissions fall for at least 10 years, it adds. But these reductions have “only partly offset” global emissions increases.

The report adds that there are several options for tackling climate change that are “technically viable”, “increasingly cost effective” and are “generally supported by the public”. 

This includes solar and wind power, the greening of cities, boosting energy efficiency, protecting forests and grasslands, reducing food waste and increasing the electrification of urban systems.

It adds that, over 2010-19, there have been large decreases in the unit costs of solar power (85%), wind (55%) and lithium ion batteries (85%). In many regions, electricity from solar and wind is now cheaper than that derived from fossil fuels, the report says.

Solar installation in the San Luis Valley. Photo credit: Western Resource Advocates

(According to the Earth Negotiations Bulletin, a group of countries including Germany, Denmark and Norway strongly argued for the report to highlight that renewables are now cheaper than fossil fuels in many regions. Finland suggested adding that fossil fuels are the “root cause” of climate change, but this was strongly opposed by Saudi Arabia.)

At the same time, there have been “large increases in their deployment”, including a global average of 10 times for solar and 100 times for electric cars, the report says. 

Falling costs and increased deployment have been boosted by public research and funding and demand-side policies such as subsidies, it says, adding:

“Maintaining emission-intensive systems may, in some regions and sectors, be more expensive than transitioning to low-emission systems (high confidence).”

(According to the Earth Negotiations Bulletin, India, supported by Brazil, said the sentence “favoured developed countries as it did not reference feasibility and challenges”.)

Despite this, a “substantial emissions gap” remains between what global GHG emissions are projected to be in 2030 and what they must be if the world is to limit global warming to 1.5C or 2C, the report says with high confidence. (The 2030 projections are derived from country climate pledges made prior to COP26 in 2021.)

This gap would “make it likely that warming will exceed 1.5C during the 21st century”, the report says with high confidence.

Pathways for how the world can limit global warming to 1.5C or 2C depend on deep global emissions cuts this decade, it adds with high confidence.

The report says with medium confidence that country climate plans ahead of COP26 would lead to around 2.8C of warming (range from 2.1-3.4C) by 2100.

However, it adds with high confidence that policies put in place by countries by the end of 2020 would not be sufficient to achieve these climate plans. This represents an “implementation gap”.

When just policies put in place by the end of 2020 are considered, around 3.2C of warming (range 2.2-3.5C) is projected by 2100, the report says with medium confidence.

The chart below, from the SPM, illustrates the warming expected in 2100 from policies implemented by 2020 (red), as well as what emissions cuts would need to look like to reach 1.5C (blue) or 2C (green).

Expected warming in 2100 from policies implemented by the end of 2020 (red), compared with emissions cuts needed to limit warming to 1.5C (blue) or 2C (green). Source: IPCC (2023) SPM.5

Speaking during a press briefing, Prof Peter Thorne, director of the ICARUS Climate Research Centre at Maynooth University in Ireland and synthesis report author, noted that the IPCC’s assessment had a cut-off date of before COP26 in 2021. He explained:

“Additional implemented policies since the cut-off date would lead to those curves drawing down a little bit, compared to where they are. But everything that has happened since the IPCC cut-off – which is outside the scope of this synthesis report – would suggest that we’re still some way off.”

(A November 2022 assessment from the independent research group Climate Action Tracker found that country climate plans for 2030 in place by that time would cause 2.4C (range 1.9-2.9C) of warming. Policies in place by that time would cause 2.7C (range 2.2-3.4C), it added.)

The report also notes that many countries have signalled intentions to achieve net-zero greenhouse gas or CO2 emissions by 2050. However, it says such pledges differ “in terms of scope and specificity, and limited policies are to date in place to deliver on them”.

In most developing countries, the rollout of low-carbon technologies is lagging behind, the report adds. This is due in part to a lack of finance and technology transfer from developed countries, it says with medium confidence.

The leveraging of climate finance for developing countries has slowed since 2018, the report says with high confidence. It adds:

“Public and private finance flows for fossil fuels are still greater than those for climate adaptation and mitigation (high confidence).”

9. What is needed to stop climate change?

“There is a brief and rapidly closing window of opportunity to secure a liveable and sustainable future for all,” the report says with high confidence.

The synthesis delivers a blunt message on what will be needed to stop climate change, saying “limiting human-caused warming requires net-zero CO2 emissions”.

(The Earth Negotiations Bulletin says there was debate over this opening sentence in section B5 of the SPM. It reports: “The authors said that a fundamental insight of AR6 is that, to hold warming at any level, net-zero [CO2] emissions are required at some point.)

The report goes on to say, with high confidence, that reaching net-zero greenhouse gas emissions would imply net-negative CO2 – and would “result in a gradual decline in surface temperatures”.

Reaching net-zero emissions requires “rapid and deep and, in most cases, immediate greenhouse gas emissions reductions in all sectors this decade”, according to the report.

Repeating language from the underlying WG3 report, it adds that global GHG emissions must peak “between 2020 and at the latest before 2025” to keep warming below 1.5C or 2C.

In contrast with the direct wording on net-zero, the report barely mentions coal, oil and gas. 

A coal train moves in front of the Black Thunder mine outside Wright in October, 2016. (Andrew Graham/WyoFile)

However, it does say net-zero would mean a “substantial reduction in overall fossil fuel use”.

Staying below 1.5C or 2C depends on cumulative carbon emissions at the time of reaching net-zero CO2 and the level of greenhouse gas emissions cuts this decade, the report says.

Specifically, net-zero CO2 needs to be reached “in the early 2050s” to stay below 1.5C:

“Pathways that limit warming to 1.5C (>50%) with no or limited overshoot reach net-zero CO2 in the early 2050s, followed by net-negative CO2 emissions. Those pathways that reach net-zero GHG emissions do so around the 2070s. Pathways that limit warming to 2C (>67%) reach net-zero CO2 emissions in the early 2070s.”

(There was some confusion on this point after a speech by UN secretary-general António Guterres launching the IPCC report. Guterres called for global net-zero emissions by 2050, with developed countries going faster, but did not say if he was referring to CO2 or GHGs.)

There is a direct link between cumulative carbon emissions and warming, with the report saying that every 1,000GtCO2 raises temperatures by 0.45C. The report says with high confidence:

“From a physical science perspective, limiting human-caused global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net-zero CO2 emissions, along with strong reductions in other greenhouse gas emissions.”

This results in “carbon budgets” that must not be exceeded if the world is to limit warming to a given level. As of the start of 2020, the remaining budget to give a 50% chance of staying below 1.5C is 500GtCO2, rising to 1,150GtCO2 for a 67% chance of staying below 2C.

(Stronger reductions of non-CO2 emissions would mean a larger carbon budget for a given temperature limit, the report notes, and vice versa.)

Some four-fifths of the total budget for 1.5C has already been used up during 1850-2019 and the last fifth would be “almost exhaust[ed]” by 2030, if emissions remained at 2019 levels.

In order to stay within the budget for 1.5C, global greenhouse gas emissions would need to fall to 43% below 2019 levels by 2030 and to 60% below by 2035, falling 84% by 2050.

Even faster reductions are required for CO2 emissions, which would fall to 48% below 2019 levels by 2030, 65% by 2035 and 99% by 2050, when they would effectively hit net-zero.

The synthesis report lists these numbers in a new table, below. While the information is not new, it had not previously been presented in an accessible format. It was added during the week-long approval process and is labelled “Table XX”.

Central (median) CO2 and GHG reductions in 2030, 2035, 2040 and 2050, relative to 2019 levels, in 97 “C1” scenarios that have a greater than 50% chance of limiting warming to 1.5C with no or limited overshoot, and in 311 “C3” scenarios that have a 67% chance of limiting warming to 2C. Numbers in square brackets indicate 5th to 95th percentile ranges across the scenarios. Note that most of these scenarios are designed to cut emissions globally at “least-cost”, meaning they “do not make explicit assumptions about global equity, environmental justice or intraregional income distribution”. Source: IPCC (2023) Table XX.

At a briefing for journalists held by the UK Science Media Centre, Dr Chris Jones, synthesis report author and research fellow at the UK’s Met Office, said: “We hope, obviously, this information is useful for the stocktake process.”

(This refers to the “global stocktake” of progress to date and the efforts needed to meet international climate goals, which is taking place this year as part of the UN climate process.)

The report outlines how the world could reach net-zero CO2 emissions via a “substantial reduction in overall fossil fuel use, minimal use of unabated fossil fuels, and use of carbon capture and storage (CCS) in the remaining fossil fuel systems”.

(The phrase “unabated fossil fuels” is defined in a footnote to the report, by comparison with “abatement”, which it says would mean “capturing 90% or more CO2 from power plants, or 50–80% of fugitive methane emissions from energy supply”.)

While the world needs to make “deep and rapid” cuts in gross emissions, the use of CO2 removal (CDR) is also “unavoidable” to reach net-zero, the report says with high confidence.

The report explains:

“[P]athways reaching net-zero CO2 and GHG emissions include transitioning from fossil fuels without carbon capture and storage (CCS) to very low- or zero-carbon energy sources, such as renewables or fossil fuels with CCS, demand-side measures and improving efficiency, reducing non-CO2 GHG emissions, and CDR.”

CDR will be needed to “counterbalance” hard-to-abate residual emissions in some sectors, for example “some emissions from agriculture, aviation, shipping and industrial processes”.

(For more detail on sectoral transitions needed to reach net-zero, see: How can individual sectors scale up climate action?)

Emphasising the challenge of limiting warming, the report says the fossil fuel infrastructure that has already been built would be enough to breach the 1.5C carbon budget, if operated in line with historical patterns and in the absence of extra abatement.

This is shown in the figure below. The top panel shows historical emissions and the remaining budgets for 1.5C or 2C, as well as emissions this decade if they remain at 2019 levels and the emissions of existing and planned fossil fuel infrastructure.

The lower panel shows historical warming and potential increases by 2050, in relation to the carbon budgets and the range of possible emissions over the same period.

Cumulative past, projected and “committed” CO2 emissions from existing and planned fossil fuel infrastructure, GtCO2, and associated global warming. Source: IPCC (2023) Figure 3.5.

Delaying emissions cuts risks “lock-in [of] high-emissions infrastructure”, the report states, adding with high confidence that this would “raise risks of stranded assets and cost-escalation, reduce feasibility, and increase losses and damages”.

The report notes that only “a small number of the most ambitious global modelled pathways” avoid temporary overshoot of the 1.5C target. However, warming “could gradually be reduced again by achieving and sustaining net-negative global CO2 emissions”.

On the other hand, the IPCC warns of “additional risks” as a result of overshoot, defined as exceeding a warming level and returning below it later. It states with high confidence:

“Overshoot entails adverse impacts, some irreversible, and additional risks for human and natural systems, all growing with the magnitude and duration of overshoot.”

The report adds that some of these impacts could make it harder to return warming to lower levels, stating with medium confidence:

“Adverse impacts that occur during this period of overshoot and cause additional warming via feedback mechanisms, such as increased wildfires, mass mortality of trees, drying of peatlands, and permafrost thawing, weakening natural land carbon sinks and increasing releases of GHGs would make the return more challenging.”

It says the risks around overshoot, as well as the “feasibility and sustainability concerns” for CDR, can be minimised by faster action to cut emissions. Similarly, development pathways that use resources more efficiently also minimise dependence on CDR.

10. How can individual sectors scale up climate action?

In order to limit warming to 2C or below by the end of the century, all sectors must undergo “rapid and deep, and in most cases, immediate greenhouse gas emissions reductions”, the report says.

Limiting warming to 1.5C with “no or limited overshoot” requires achieving net-zero CO2 emissions in the early 2050s. To keep warming to 2C, net-zero CO2 must be achieved “around the early 2070s”. 

It continues, with medium confidence

Source: IPCC (2023) Full report, p68

Reducing emissions from the energy sector requires a combination of actions, the report says: a “substantial reduction” in the use of fossil fuels; increased deployment of energy sources with zero or low emissions, “such as renewables or fossil fuels with CO2 capture and storage” (CCS); improving energy efficiency and conservation; and “switching to alternative energy carriers”. 

For sectors that are harder to decarbonise, such as shipping, aviation, industrial processes and some agriculture-related emissions, the report notes that using carbon dioxide removal (CDR) technologies to counterbalance these residual emissions “is unavoidable”. 

Graphic credit: The Nature Conservancy

The language around CCS and CDR was some of the most contentious during the approval session. According to the Earth Negotiations Bulletin, Germany “suggested including a brief overview of the feasibility and current deployment of different CDR methods”, with France adding that policymakers must be made aware of the associated challenges.

But Saudi Arabia countered that if these barriers were made explicit in this section, it “would require similar balancing language on the feasibility of solar and renewables elsewhere in the report”. 

Similar discussions were had around CCS, with the authors ultimately agreeing to add a sub-paragraph in a footnote that details both the limits and benefits of CCS, at the urging of Germany and Saudi Arabia, respectively. 

The report discusses several technologies across a range of maturity, removal and storage potential and costs. It finds that “all assessed modelled pathways that limit warming to 2C (>67%) or lower by 2100” rely, at least in part, on mitigation from agriculture, forestry and other land use (AFOLU). Such approaches are currently “the only widely practised CDR methods”, the report notes.

However, it details trade-offs and barriers to large-scale implementation of AFOLU-based mitigation, including climate change impacts, competing demands for land use, endangering food security and violation of Indigenous rights. 

The report also discusses sector-specific actions that can be taken in order to limit emissions and climate impacts. These transformations, it says, are “required for high levels of human health and well-being, economic and social resilience, ecosystem health and planetary health”.

The chart below shows near-term feasibility of adaptation (left) and mitigation (right) options, divided across six sectors (top left to bottom right): energy supply; land, water and food; settlements and infrastructure; health; society, livelihood and economy; and industry and waste.

For adaptation options, the figure shows the potential for synergies with mitigation strategies and the feasibility of these options up to 1.5C of warming, from low (light purple) to high (dark blue). The dots in each box represent the confidence level, from low (one dot) to high (three dots).

On the right, mitigation options are presented with their potential contribution to emissions reductions by 2030, in GtCO2e per year. The colours indicate the cost of each option, from low (yellow) to high (red), with blue indicating options that are cheaper than fossil fuels. Some of the mitigation options with the highest potential for cost-saving are solar and wind power, efficient vehicles, lighting and other equipment, and public transit and cycling.

Feasibility of climate adaptation options and their synergies with mitigation actions (left) and potential contributions of mitigation options to emissions reductions by the end of the decade (right). Source: IPCC (2023) Figure 4.4a

Some of these mitigation options relate to changes in energy demand, rather than supply. This includes “changes in infrastructure use, end-use technology adoption and socio-cultural and behavioural change”, the report says, noting that such changes can reduce emissions in end-use sectors by 40-70% by mid-century.

The chart below shows the mid-century mitigation potential of demand-side changes across a range of sectors: food (including diet and waste), land transport, buildings, industry and electricity. The green arrows represent the mitigation potential in GtCO2 per year. 

The mitigation potential, in GtCO2e per year, of five demand-side sectors (top to bottom): food, land transport, buildings, industry and electricity. The grey bar shows the additional emissions that continued electrification will add. Source: IPCC (2023) Figure 4.4b

Section 4.5 of the report goes into detail about near-term mitigation and adaptation, in subsections covering energy systems; industry; cities, settlements and infrastructure; land, ocean, food and water; health and nutrition; and society, livelihoods and economies. At the urging of India (supported by Saudi Arabia and China) in the approval session, the report notes that the availability and feasibility of these options differs “across systems and regions”.

On energy systems, the report says with high confidence that “major energy system transitions” are required and with very high confidence that adaptation “can help reduce climate-related risks to the energy system”, including extreme events that can damage or otherwise affect energy infrastructure.

It notes that many of the options for large-scale emissions reductions are “technically viable and supported by the public”. It adds:

“Maintaining emission-intensive systems may, in some regions and sectors, be more expensive than transitioning to low emission systems.”

However, adaptation measures for certain types of power generation, such as hydropower, have “decreasing effectiveness at higher levels of warming” beyond 1.5C or 2C, the report notes. Reducing vulnerabilities in the energy sector requires diversification and changes on the demand side, including improving energy efficiency.

The strategies to reduce industrial emissions “differ by type of industry”, the report says. Light manufacturing can be “largely decarbonised” through available technologies and electrification, while decarbonising others will require the use of carbon capture and storage and the development of new technologies. The report adds that extreme events will cause “supply and operational disruptions” across many industries.

“Effective mitigation” strategies can be implemented at every step of building design, construction and use, the report says. It notes that demand-side measures can help reduce transportation-related emissions, as can re-allocating street space for pedestrians and cyclists and enabling telework. 

With high confidence, it says: 

“Key infrastructure systems including sanitation, water, health, transport, communications and energy will be increasingly vulnerable if design standards do not account for changing climate conditions.”

The report also says that “green” and “blue” infrastructure have myriad benefits: climate change mitigation, reducing extreme weather risk and improving human health and livelihoods.

AFOLU, as well as the ocean, offer “substantial mitigation and adaptation potential…that could be upscaled in the near term across most regions”, the report finds. It notes that conservation and restoration of ecosystems provide “the largest share” of this potential. It reads:

Source: IPCC (2023) Full report, p73

Such actions must be taken with the cooperation and involvement of local communities and Indigenous peoples, the report adds.

With very high confidence, the report states that “mainstream[ing]” health considerations into policies will benefit human health. There is also high confidence in the existing availability of “effective adaptation options” in the health sector, such as improving access to drinking water and vaccine development. The report states with high confidence:

“A key pathway to climate resilience in the health sector is universal access to healthcare.”

The report calls for improving climate education, writing with high confidence

“Climate literacy and information provided through climate services and community approaches, including those that are informed by Indigenous knowledge and local knowledge, can accelerate behavioural changes and planning.”

It says that many types of adaptation options “have broad applicability across sectors and provide greater risk reduction benefits when combined”. It also calls for “accelerating commitment and follow-through” from private sector actors.

11. What does the report say about adaptation?

The world is not adapting fast enough to climate change – and limits to adaptation have already been reached in some regions and ecosystems, the report says.

It says with very high confidence that there has been progress with adaptation planning and roll-out in all sectors and regions – and that accelerated adaptation will bring benefits for human wellbeing.

Adaptation to water-related risks make up more than 60% of all documented adaptation practices, the report says with high confidence

Examples of effective adaptation have occurred in food production, such as through planting trees on cropland, diversification in agriculture and water management and storages, the report says with high confidence.

“Ecosystem-based approaches”, such as urban greening and restoring wetlands and forests, have been effective in “reducing flood risks and urban heat”, it adds with high confidence.

In addition, combinations of “non-structural measures”, such as early warning systems, and structural measures such as levees have reduced deaths from flooding, the report says with medium confidence.

But, despite progress, most adaptation is “fragmented, incremental, sector-specific and unequally-distributed across regions”, the report says, adding:

“Adaptation gaps exist across sectors and regions, and will continue to grow under current levels of implementation, with the largest adaptation gaps among lower income groups.” 

Key barriers to adaptation include a lack of financial resources, political commitment and a “low sense of urgency”, the report says.

The total amount spent on adaptation has increased since 2014. However, there is currently a widening gap between the costs of adaptation and the amount of money set aside for adaptation, according to the report.

It says with very high confidence that the “overwhelming majority” of climate finance goes towards mitigation rather than adaptation. (See: Why is finance an ‘enabler’ and ‘barrier’ for climate action?)

It adds with medium confidence that financial losses caused by climate change can reduce funds available for adaptation – hence, leaving countries more vulnerable to future impacts. This is particularly true for developing and least-developed countries.

The report says with medium confidence that some people are already experiencing “soft limits” to adaptation. “Soft limits” are those where there is currently no way to adapt to the change, but there may be a way in the future. This includes small-scale farmers and households living in low-lying coastal areas.

Some areas have reached “hard limits” to adaptation, where no further adaptation to climate change is possible, the report says with high confidence. This includes some rainforests, tropical coral reefs, coastal wetlands, and polar and mountain ecosystems.

In the future, “adaptation options that are feasible and effective today will become constrained and less effective with increasing global warming”, the report says. It adds:

“With increasing global warming, losses and damages will increase and additional human and natural systems will reach adaptation limits.”

For example, the effectiveness of reducing climate risks by switching crop varieties or planting patterns – commonplace on farms today – is projected to decrease above 1.5C of warming, the report says with high confidence. The effectiveness of on-farm irrigation is projected to decline above 3C, it adds.

Above 1.5C of warming, small island populations and regions dependent on glaciers for freshwater could face hard adaptation limits, the report says with medium confidence.

At this level of warming, ecosystems such as coral reefs, rainforests and polar and mountain ecosystems will have surpassed hard adaptation limits – meaning some ecosystem-based approaches will become ineffective, the report says with high confidence.

By 2C, soft limits are projected for multiple staple crops, particularly in tropical regions, it says with high confidence. By 3C, hard limits are projected for water management in parts of Europe, it says with medium confidence

Even before limits to adaptation are reached, adaptation cannot prevent all loss and damage from climate change, the report says with high confidence. (See: What does the report say on loss and damage?)

(According to the Earth Negotiations Bulletin, China requested removing a reference to “adaptation limits” from one of the headline statements of the SPM. It was opposed by countries including the UK, Denmark, Germany, Saint Kitts and Nevis, the Netherlands, Switzerland, Mexico and Belize.) 

The report says with high confidence that sea level rise poses a “distinct and severe adaptation challenge”. This is because it requires dealing with both slow onset changes and increases in extreme sea level events such as storm surges and flooding.

The graphic below illustrates some of the adaptation responses to sea level rise, including the time it takes for implementation and their typical intended lifetimes.

Adaptation responses for sea level rise. Source: IPCC (2023) Figure 3.4b

“Ecosystem-based” approaches include enhancing coastal wetlands. Such approaches come with co-benefits for biodiversity and reducing emissions, but start to become ineffective above 1.5C of warming, the report says with medium confidence.

“Sediment-based” approaches include seawalls. These can be ineffective “as they effectively reduce impacts in the short-term but can also result in lock-ins and increase exposure to climate risks in the long-term”, the report says.

Planned relocation methods can be more effective if they are aligned with sociocultural values and involve local communities, the report says.

The report warns with high confidence that there is now more evidence of “maladaptation” – actions intended to adapt to climate change that create more risk and vulnerability.

Examples of maladaptation include new urban buildings that cannot easily be adjusted for climate risks or high-cost irrigation systems for agriculture in areas where droughts are projected to intensify, the report says.

Maladaptation “especially affects” marginalised and vulnerable groups, including Indigenous peoples, ethnic minorities, low-income households and people living in informal settlements. This can “reinforce and entrench” existing inequalities.

12. What are the benefits of near-term climate action?

The report is clear that fast action to mitigate emissions and adapt to climate impacts has a range of benefits – but acknowledges that it will likely be disruptive and have high up-front costs.    

The rate of climate change and the associated risks “depend strongly” on near-term climate action, the report says. The SPM notes with high confidence

“The choices and actions implemented in this decade will have impacts now and for thousands of years.” 

The overarching benefit of near-term mitigation action is less global warming over time and thereby fewer negative impacts, such as extreme weather events. 

Accelerated mitigation measures would also reduce future adaptation costs alongside other benefits, such as reducing the risk of irreversible climate changes, the synthesis report says.

A quick reduction in methane emissions, in particular, can limit near-term warming, the report says with high confidence. Methane has a much shorter lifespan in the atmosphere than CO2.

Delaying actions to prevent further warming will lead to a larger temperature rise, which will, in turn, make adaptation measures less effective, it says.

Adaptation actions can take a long time to be put in place. The report stresses that long-term planning and faster implementation, especially in this decade, “is important to close adaptation gaps”. 

Adaptation measures, the report adds, can improve agricultural productivity, innovation, health and wellbeing, food security, livelihood and biodiversity conservation.

Text on mitigation co-benefits for sustainable development Source: IPCC (2023) Full report, p59

There are other co-benefits to cutting emissions and taking faster action on adaptation. The SPM says that “deep, rapid and sustained” action in this decade would lower air pollution, spark more walking and cycling and prompt more sustainable, healthy diets. 

The money saved from a health perspective as a result of improved air quality “can be of the same order of magnitude as mitigation costs, and potentially even larger”, the report adds.

There are further economic benefits to near-term climate action, but the SPM says the cost-benefit analysis “remains limited” in assessing all avoided damages. 

Outside of the benefits of avoiding possible damages, the economic and social benefits of limiting global warming to 2C exceeds mitigation costs in most literature, the SPM says with medium confidence. 

The SPM says that faster mitigation with emissions peaking earlier increases the co-benefits of action and reduces risks and costs in the long-term. 

It further says, with high confidence, that near-term actions require “high up-front investments and potentially disruptive changes”. 

Barriers to deploy mitigation and adaptation actions need to be removed or reduced to utilise these options at scale, the report says.

To scale up these actions, the report says that both low- and high-cost options, such as using more renewables, making buildings more efficient and using electric vehicles, are required to avoid future lock-ins, advance innovation and start transformational changes.

Leaf charging at the Lionshead parking facility in Vail September 30, 2021.

The impacts of these changes can be “moderated” by reforms and policies in order to accelerate climate action such as improving access to finance for low-emissions infrastructure and technologies, especially in developing countries. 

Delaying action comes with multiple challenges, the report says, such as cost escalation risks, lock-in of infrastructure and stranded assets.

In other words, continuing to install unabated fossil fuel infrastructure will “lock-in” emissions into the future. And taking action on fossil-fuel burning sooner rather than later would limit the size of stranded assets – such as fossil-fuel infrastructure – that will be worth a lot less money in future in a world more reliant on low-carbon energy. 

Delaying action on this would increase policy risks and may endanger efforts to limit global warming, the report says with high confidence. 

Climate action is enabled by good climate governance providing an overall direction, the report says. 

This involves setting targets, including climate action in different policy areas, prioritising equitable decision-making and enhancing access to finance. The report adds that climate action benefits from drawing on a diverse range of knowledge. 

13. Why is finance an ‘enabler’ and ‘barrier’ for climate action?

Finance is one of the “critical enablers” to speed up climate action, the synthesis report outlines, and lack of funding is a barrier to progress. 

Difficulty accessing climate finance slows down both mitigation and adaptation action, particularly in developing countries, the report warns. Improving access to funds will help to accelerate climate action, the report says with very high confidence. 

It adds that funding for mitigation and adaptation needs to increase “many-fold” to achieve climate goals, address risks and speed up investment in emissions reductions. 

Global climate finance flows have increased and financing channels have broadened over the past decade, but the report notes that average growth has slowed since 2018. The report adds with high confidence

“Public and private finance flows for fossil fuels are still greater than those for climate adaptation and mitigation.”

It assesses that climate funding is “uneven” and has “developed heterogeneously across regions and sectors”, adding that the money falls short of what is needed to slash emissions and adapt to climate impacts.

There is enough global capital to close investment gaps, the report says, but “barriers” are preventing this funding being used instead for climate action. 

Closing gaps and improving access to finance, alongside other actions, can “act as a catalyst for accelerating” climate action, the SPM says. The report builds on this, saying: 

“​​Accelerated support from developed countries and multilateral institutions is a critical enabler to enhance mitigation and adaptation action and can address inequities in finance, including its costs, terms and conditions, and economic vulnerability to climate change.”

Many developing countries do not have enough financial resources for adaptation to help reduce associated economic and non-economic losses and damages, the report says. 

The SPM outlines with high confidence that increasing access to finance can help tackle “soft”, avoidable adaptation limits and avert some of the rising risks of climate change. (See: What does the report say about adaptation?)

The “overwhelming majority” of climate finance is geared towards mitigation. But this still falls short, the SPM saysadding with medium confidence

“Average annual modelled mitigation investment requirements for 2020 to 2030 in scenarios that limit warming to 2C or 1.5C are a factor of three to six greater than current levels, and total mitigation investments (public, private, domestic and international) would need to increase across all sectors and regions.”

Limited access to funding is listed as one of the key barriers to a number of actions including the adoption of low-emissions technology in developing countries. 

Harmful impacts of climate change can further reduce a nation’s climate financial resources by causing losses and damages and also impeding economic growth. This adds to the financial constraints for adaptation, especially in developing and least developed countries. 

The largest climate finance gaps and opportunities exist in developing countries, the report says, adding that more support is needed from developed nations and multilateral institutions to address inequities. 

This could come in the form of larger public grants for climate funding “for vulnerable regions, e.g., in sub-Saharan Africa,” the report says. It adds that these would be cost-effective and have high social returns in terms of access to basic energy.

Reducing the barriers standing in the way of committing more money to climate action would require “clear signalling and support by governments” through actions such as decreasing the perceived risks of climate investments and increasing the returns, the SPM says.  

Central banks, investors and other financial actors can change the “systemic underpricing of climate-related risks” and also reduce the “widening disparities” between the money available and the amount required, the SPM adds, noting: 

“Public finance is an important enabler of adaptation and mitigation, and can also leverage private finance.”

Developed countries pledged to provide $100bn in climate funding each year by 2020 to help developing countries deal with climate change. The SPM notes that, as of 2018, finance levels were below this goal. (In 2021, Carbon Brief analysed why climate finance flows are falling short.)

According to the Earth Negotiations Bulletin, India, supported by Saudi Arabia and Brazil, requested a reference to this goal in a section on the adoption of low-emission technologies to highlight the finance gap for developing countries. 

Tejal Kanitkar, India. Credit: IISD

The final report does reference the missed pledge elsewhere, but the text of low-emission technologies instead refers more broadly to the constraints of “limited finance”. 

The SPM says that climate-resilient development – prioritising climate in all aspects of decision-making and policies – is aided by more international cooperation to improve access to finance and better align climate finance flows with the money required.

The report says faster global financial cooperation is key to aiding low-emission and just transitions. (A just transition is one in which workers and their communities are supported in the shift to a low-carbon economy, which is central to the idea of climate justice.) It can also address inequities in access to finance. 

In order to scale-up financial flows, the report says there must be lower regulatory market barriers, a stronger alignment of public finance and more public funding in an effort to reduce the perceived risks of low-emission investments. 

14. What are the co-benefits for the Sustainable Development Goals?

The Sustainable Development Goals (SDGs) were adopted by all UN member states in 2015 as the 2030 Agenda for Sustainable Development.

Comprising 17 goals, this “shared blueprint” for people and the planet recognises that ending poverty “and other deprivations” must accompany strategies that improve health, education, reduce inequality while combating climate change and protecting oceans and forests.

The synthesis report lays out how climate adaptation and mitigation actions can translate into co-benefits that aid countries’ efforts to meet their SDGs.

According to the report, both sets of actions have more potential synergies than potential trade-offs with the SDGs. This, however, depends on the scale and context of how mitigation and adaptation measures are implemented, the interactions between and within different sectors involved, cooperation between countries, governance, policy design and how these options are timed, sequenced and stringently deployed.

Ending “extreme poverty, energy poverty and providing decent living standards to all, consistent with sustainable development objectives…can be achieved without significant global emissions growth”, the report states with high confidence. 

The report’s summary recognises that countries are at different levels of development, seeking to improve the well-being of people. With high confidence, it states:

“Development priorities among countries also reflect different starting points and contexts, and enabling conditions for shifting development pathways towards increased sustainability will therefore differ, giving rise to different needs.”

Nonetheless, many mitigation and adaptation systems can help countries meet their near-term development goals in energy, urban and land systems, the report says with high confidence. 

Comanche Generating Station. Photo credit: Allen Best/Big Pivots

For instance, better air quality and improved health are some of the many co-benefits of deploying low-carbon energy systems, while urban mass transit powered by these systems can contribute to health, employment, energy security and “deliver equity”. 

Conserving, protecting and restoring ecosystems, while managing them to help communities adapt to climate impacts, can help regions attain their food security and biodiversity conservation goals, the report says with high confidence

In countries and regions that are highly dependent on fossil fuels – not just for energy, but revenues and jobs – mitigating risk calls for “just transition principles, processes and practices” and policies that promote economic and energy diversification, the SPM says with high confidence.

Mitigation actions that are embedded within a wider development context can, therefore, make for faster, deeper and wider emissions reductions, it states with medium confidence. 

But to design “context-relevant” actions and plan for their implementation “requires considering people’s needs, biodiversity, and other sustainable development dimensions”, the report states with very high confidence.

Importantly, the report calls “effective governance” to limit potential trade-offs of some mitigation choices – such as the risks posed by large-scale afforestation and bioenergy projects to food systems, biodiversity, ecosystems and livelihoods, it says with high confidence.

Crucially, this requires “adequate institutional capacity at all levels” to safeguard against trade-offs.

Mitigation and adaptation actions taken together – accounting for trade-offs – can benefit not just human well-being, but deliver better ecosystem and planetary health, the report states with high confidence. Social safety nets and land restoration are examples that serve both adaptation and mitigation goals, with co-benefits for poverty reduction and food security. 

However, there will be trade-offs, the report cautions. But these can be “evaluated and minimised” by giving weight to “capacity building, finance, technology transfer, governance, development, gender and social equity considerations with meaningful participation of local communities, Indigenous peoples and vulnerable populations”, it states with high confidence.

15. What does the report say about equity and inclusion?

“Equity remains a central element in the UN climate regime,” the SPM says. The report has a section dedicated to “equity and inclusion in climate change action”, which discusses how to ensure that those most vulnerable to the impacts of climate change can contribute to and benefit from climate mitigation and adaptation efforts.

The SPM says that “ambitious mitigation pathways imply large and sometimes disruptive changes in economic structure”. This can include a “shifting of income and employment” during the transition to low-emissions activities. 

But the report has high confidence that “social safety nets” and “redistributive policies” that “shield the poor and vulnerable” can resolve trade-offs for a range of sustainable development goals, such as education, hunger, poverty, gender and energy access.

For example, it has high confidence that “while some jobs may be lost, low-emissions development can also open up opportunities to enhance skills and create jobs”. The report emphasises the importance of “broadening equitable access” to the relevant finance, technologies and governance.

It adds: 

“Equity, inclusion, just transitions, broad and meaningful participation of all relevant actors in decision making at all scales enable deeper societal ambitions for accelerated mitigation, and climate action more broadly, and build social trust, support transformative changes and an equitable sharing of benefits and burdens”.

The report says that between 3.3 and 3.6 billion people are living in “contexts that are highly vulnerable to climate change”, where vulnerability is highest in “locations with poverty, governance challenges and limited access to basic services and resources, violent conflict and high levels of climate-sensitive livelihoods”. 

It says that adaptation can be used to moderate the risks of climate change and the authors have high confidence that “adaptation progress is unevenly distributed with observed adaptation gaps”. The report adds:

“Present development challenges causing high vulnerability are influenced by historical and ongoing patterns of inequity such as colonialism, especially for many Indigenous Peoples and local communities.”

To effectively address adaptation gaps and avoid maladaptation, the report says that “meaningful participation and inclusive planning, informed by cultural values, Indigenous knowledge, local knowledge, and scientific knowledge can help”.

The report also notes that different countries have their own priorities for development, which give rise to differing needs.

For example, it says that “in several countries just transition commissions, task forces and national policies have been established”, while in others, the principles of a just transition need to be integrated into policies through “collective and participatory decision-making processes”.

This section of the report also discusses behavioural interventions. It has high confidence that “individuals with high socioeconomic status contribute disproportionately to emissions, and have the highest potential for emissions reductions”. It says there are many options for reducing emissions from this group, which can be supported by policies, infrastructure, and technology.

Meanwhile, it has high confidence that, for lower-income groups, “eradicating extreme poverty, energy poverty, and providing decent living standards to all in these regions in the context of achieving sustainable development objectives, in the near-term, can be achieved without significant global emissions growth”.