From Inside Climate News (Bob Berwyn):
A new IPCC science assessment, coming before COP26 in November, called for immediate action and showed that this summer’s extremes are only a mild preview of the decades ahead.
Amidst a summer of fires, floods and heat waves, scientists on Monday delivered yet another reminder that burning more fossil fuels in the decades ahead will rapidly intensify the impacts of global warming. Only pulling the emergency brake right now on greenhouse gas emissions can stop the planet from heating to a dangerous level by the end of the century, the scientists’ report concluded.
The report, Climate Change 2021: the Physical Science Basis, is the first installment of the Intergovernmental Panel on Climate Change’s Sixth Assessment Report (AR6), which will be completed in 2022. It was approved Aug. 6 by 195 member governments of the IPCC.
The report, by the panel’s Working Group I, assesses the physical science of climate change. It found that global warming is worsening deadly extremes like droughts and tropical storms and that every part of the planet is affected.
The report, by the panel’s Working Group I, assesses the physical science of climate change. It found that global warming is worsening deadly extremes like droughts and tropical storms and that every part of the planet is affected.
“We see this signal in all regions. No region is really spared from climate change,” said Sonia Seneviratne, a coordinating lead author of the report and a climate researcher at ETH Zürich, where she focuses on climate extremes. The report shows that “Immediate reductions of CO2 emissions would be needed to retain a chance to limit global warming close to the 2.7 degrees Fahrenheit of warming targeted by the Paris climate agreement,” she added.
Seneviratne said that it had become apparent as the scientists worked on the report that many parts of the world were vulnerable to compounded climate impacts, with “extremes of different types leading to more impacts when combined, such as the co-occurrence of heatwaves and droughts.”
Recent examples include the deadly heat wave in the Pacific Northwest that was followed by a surge of forest fires in drought-stressed, dying forests. The warmer the planet, the higher the chances of crop-killing extremes affecting different agricultural areas at the same time, she said.
The IPCC report found that, without human-caused warming, there was “a near zero probability” of some of the deadliest recent heat waves, as well as other extremes like flooding rain. “We do see we need action immediately if we want to limit warming to somewhere around 1.5 degrees Celsius,” Seneviratne added.
That global climate target, equivalent to 2.7 degrees Fahrenheit warming from pre-industrial levels, was set in 2015 as part of the Paris climate agreement, and was based on the last major climate assessment from the IPCC. The new report confirms that beyond that level of warming, parts of the climate system, like the meltdown of ice sheets that raise sea level, could spiral out of control.
IPCC vice-chairwoman Ko Barrett, a deputy administrator with the National Ocean and Atmospheric Administration, said the new report provides “unequivocal” confirmation that humans are warming the planet to a dangerous level, causing widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere in every region of the world and across the whole climate system.
It also reflects “major advances” in understanding how “climate change intensifies specific weather and climate events such as extreme heat waves and heavy rainfall events,” said IPCC Working Group I Co-Chairwoman Valérie Masson-Delmotte, a research director at the French Alternative Energies and Atomic Energy Commission.
New climate models, with more accurate data of critical climate systems like clouds, also helped make the most accurate projections to date of how the climate would respond if greenhouse gas emissions stopped. While there are still some big question marks about how much CO2 permafrost and forests will take up and release in the future, the report suggests that the climate could begin stabilizing 20 to 30 years after greenhouse gas concentrations level off.
There is also no longer any question that global warming is changing the planet’s water cycle, the report found, bringing more intense rainfalls and flooding, as well as more intense droughts in many regions. Farther north and south, in higher latitudes, precipitation is likely to increase, but expected to decline in many already dry subtropical zones.
Since 1990, the panel has released 5 major climate science assessments, about 5 to 6 years apart, with special reports focusing on specific subjects in between. Going into the global COP26 climate talks in Glasgow in November, the latest science assessment gives negotiators a robust scientific basis that can empower decision-makers to take critical action.
Steve Cornelius, a former climate negotiator with the United Kingdom government who is now the chief climate advisor for WWF, said the 2018 IPCC report, which focused on the consequences of planetary warming of more than 1.5 degrees Celsius, provided an example of how science can spur action.
“Policymakers take notice of reports from the IPCC,” Cornelius said. “We have a net zero (carbon dioxide emissions) target in the UK that came about as a direct response to the IPCC’s 2018 report. That came out, and the government asked the Committee on Climate Change to come up with a plan for net-zero.” That would not have happened without the report, he said.
But at a global level, the response to the IPCC reports has not measured up to the urgency of the situation, said Saleemul Huq, director of the International Center for Climate Change and Development in Dhaka, Bangladesh.
“Past IPCC reports have served as the basis for promises to tackle global warming,” he said “But the actions that have actually been taken in practice neither conform to what countries promised to do and are nowhere near where the science says we must be.” The new report, he said, shows “how bad things are getting and why the world needs to speed up actions in line with the scientific needs.”
Talk of Tipping Points
Stephan Singer, a senior climate advisor with Climate Action Network International who is based in Brussels, represented environmental and climate activist groups during recent IPCC meetings. ”It was refreshing to see the U.S. back in the caucus of civilized nations,” he said, as the scientists and government reviewers finalized the report.
He added that the participation by environmental groups helped ensure that the IPCC didn’t stray away from the 1.5C warming target.
“There was a fear that the 1.5 target might be dropped,” Singer said. “We wanted to make sure that it stays in there as an option. But it’s tough and challenging, and we’re losing time every day.”
Singer said the environmental groups wanted “to make sure the report makes clear the need for urgent action.”
“We need to do things now in order to have a chance to meet net-zero,” he said, “and that includes protecting and restoring natural carbon sinks, like forests. And people need to understand this is the only IPCC report coming out before COP26 and before the United Nations General Assembly so, the language must be really clear.”
“All scenarios investigated by the IPCC show that global warming will probably exceed 1.5 degrees Celsius in the next few decades,” Singer said, showing how close we are to dangerous thresholds.
“The IPCC is strongly talking about tipping points,” Singer said, “ We can’t rule out significant forest diebacks and ice sheets falling apart, or other things that can feed back and make the warming even worse. We’re playing Russian roulette with 5 bullets in the gun.”
Same Message, Fewer ‘Weasel Words’
Scott Denning, an atmospheric scientist at Colorado State University, said the new IPCC report essentially hammers home the same message as all its predecessors, dating back to 1990.
“Each report has less and less weasel words, but it’s still pretty much the same message,” he said. “Adding CO2 to the atmosphere warms up the world.”
One new element of this latest IPCC science assessment is a more regional breakdown of global warming impacts, and some of its conclusions are underlined by current conditions in the Western United States. Water supplies in the West are drying to a trickle after a 20-year drought, dangerous heat waves are lasting longer and thousands of square miles of forest have burned up in the past few years.
Denning said he recently analyzed 40 years of data from a network of 800 snow sensors, finding that about half those sites have lost half of their spring snowpack in the last 40 years.
“Holy crap, we are in trouble if 1 degree Celsius of warming has cost us half our mountain snowpack,” he said. “We’ll rejigger our systems to deliver some water, but we can’t support 75 million people in the West without a mountain snowpack.”
Ida Ploner, a 14-year-old activist with Fridays For Future in Vienna, Austria said the new science report once again shows the urgency of ending carbon dioxide emissions now, especially for her generation, which will live with the consequences of the decisions made today.
“It’s not that it’s going to get just a little warmer,” said Ploner, who has been organizing protests against highway projects that would lead to more greenhouse gas emissions. “This is an existential question. Earth is burning and time is running out.”
The new report could be another wakeup call, she said, but in recent years, other landmark reports have done nothing more than trigger greenwashing campaigns.
“It takes away a bit of hope, when we keep seeing more reports and nothing happens,” she said. “It shouldn’t be my job at 14 to ensure that I have a future. We have leaders for that, but they aren’t doing it, and it’s too important to turn away. We need to show that all of society is mad and that we are going to do something about it.”
The water cycle is intensifying as the climate warms, IPCC report warns – that means more intense storms and flooding
The world watched in July 2021 as extreme rainfall became floods that washed away centuries-old homes in Europe, triggered landslides in Asia and inundated subways in China. More than 900 people died in the destruction. In North America, the West was battling fires amid an intense drought that is affecting water and power supplies.
Water-related hazards can be exceptionally destructive, and the impact of climate change on extreme water-related events like these is increasingly evident.
In a new international climate assessment published Aug. 9, 2021, the Intergovernmental Panel on Climate Change warns that the water cycle has been intensifying and will continue to intensify as the planet warms.
The report, which I worked on as a lead author, documents an increase in both wet extremes, including more intense rainfall over most regions, and dry extremes, including drying in the Mediterranean, southwestern Australia, southwestern South America, South Africa and western North America. It also shows that both wet and dry extremes will continue to increase with future warming.
Why is the water cycle intensifying?
Water cycles through the environment, moving between the atmosphere, ocean, land and reservoirs of frozen water. It might fall as rain or snow, seep into the ground, run into a waterway, join the ocean, freeze or evaporate back into the atmosphere. Plants also take up water from the ground and release it through transpiration from their leaves. In recent decades, there has been an overall increase in the rates of precipitation and evaporation.
A number of factors are intensifying the water cycle, but one of the most important is that warming temperatures raise the upper limit on the amount of moisture in the air. That increases the potential for more rain.
This aspect of climate change is confirmed across all of our lines of evidence: It is expected from basic physics, projected by computer models, and it already shows up in the observational data as a general increase of rainfall intensity with warming temperatures.
Understanding this and other changes in the water cycle is important for more than preparing for disasters. Water is an essential resource for all ecosystems and human societies, and particularly agriculture.
What does this mean for the future?
An intensifying water cycle means that both wet and dry extremes and the general variability of the water cycle will increase, although not uniformly around the globe.
Rainfall intensity is expected to increase for most land areas, but the largest increases in dryness are expected in the Mediterranean, southwestern South America and western North America.
Globally, daily extreme precipitation events will likely intensify by about 7% for every 1 degree Celsius (1.8 degrees Fahrenheit) that global temperatures rise.
Many other important aspects of the water cycle will also change in addition to extremes as global temperatures increase, the report shows, including reductions in mountain glaciers, decreasing duration of seasonal snow cover, earlier snowmelt and contrasting changes in monsoon rains across different regions, which will impact the water resources of billions of people.
What can be done?
One common theme across these aspects of the water cycle is that higher greenhouse gas emissions lead to bigger impacts.
The IPCC does not make policy recommendations. Instead, it provides the scientific information needed to carefully evaluate policy choices. The results show what the implications of different choices are likely to be.
One thing the scientific evidence in the report clearly tells world leaders is that limiting global warming to the Paris Agreement target of 1.5 C (2.7 F) will require immediate, rapid and large-scale reductions in greenhouse gas emissions.
Regardless of any specific target, it is clear that the severity of climate change impacts are closely linked to greenhouse gas emissions: Reducing emissions will reduce impacts. Every fraction of a degree matters.
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IPCC climate report: Profound changes are underway in Earth’s oceans and ice – a lead author explains what the warnings mean
Humans are unequivocally warming the planet, and that’s triggering rapid changes in the atmosphere, oceans and polar regions, and increasing extreme weather around the world, the Intergovernmental Panel on Climate Change warns in a new report.
The IPCC released the first part of its much anticipated Sixth Assessment Report on Aug. 9, 2021. In it, 234 scientists from around the globe summarized the current climate research on how the Earth is changing as temperatures rise and what those changes will mean for the future.
What are the IPCC report’s most important overall messages in your view?
At the most basic level, the facts about climate change have been clear for a long time, with the evidence just continuing to grow.
As a result of human activities, the planet is changing at a rate unprecedented for at least thousands of years. These changes are affecting every area of the planet.
While some of the changes will be irreversible for millennia, some can be slowed and others reversed through strong, rapid and sustained reductions in greenhouse gas emissions.
But time is running out to meet the ambitious goal laid out in the 2015 international Paris Agreement to limit warming to well below 2 degrees Celsius above preindustrial levels (2 C equals 3.6 degrees Fahrenheit). Doing so requires getting global carbon dioxide emissions on a downward course that reaches net zero around or before 2050.
What are scientists most concerned about right now when it comes to the oceans and polar regions?
Global sea level has been rising at an accelerating rate since about 1970, and over the last century, it has risen more than in any century in at least 3,000 years.
In the years since the IPCC’s Fifth Assessment Report in 2013 and the Special Report on the Ocean and Cryosphere in a Changing Climate in 2018, the evidence for accelerating ice sheet loss has become clearer.
Over the last decade, global average sea level has risen at a rate of about 4 millimeters per year (1.5 inches per decade). This increase is due to two main factors: the melting of ice in mountain glaciers and at the poles, and the expansion of water in the ocean as it takes up heat.
Ice sheets in particular are primarily responsible for the increase in the rate of sea level rise since the 1990s. There is clear evidence tying the melting of glaciers and the Greenland Ice Sheet, as well as ocean warming, to human influence. Sea level rise is leading to substantial impacts on coastal communities, including a near-doubling in the frequency of coastal flooding since the 1960s in many sites around the world.
Since the previous reports, scientists have made substantial advances in modeling the behavior of ice sheets. At the same time, we’ve been learning more about ice sheet physics, including recognizing the potential ways ice sheets can become destabilized. We don’t well understand the potential speed of these changes, but they have the potential to lead to much more rapid ice sheet loss if greenhouse gas emissions grow unchecked.
These advances confirm that sea level is going to continue to rise for many centuries to come, creating an escalating threat for coastal communities.
Sea level change through 2050 is largely locked in: Regardless of how quickly nations are able to lower emissions, the world is likely looking at about 15 to 30 centimeters (6 to 12 inches) of global average sea level rise through the middle of the century.
But beyond 2050, sea level projections become increasingly sensitive to the world’s emissions choices. If countries continue on their current paths, with greenhouse gas emissions likely to bring 3-4 C of warming (5.4-7.2 F) by 2100, the planet will be looking at a most likely sea level rise of about 0.7 meters (a bit over 2 feet). A 2 C (3.6 F) warmer world, consistent with the Paris Agreement, would see lower sea level rise, most likely about half a meter (about 1.6 feet) by 2100.
What’s more, the more the world limits its greenhouse gas emissions, the lower the chance of triggering instabilities in the polar ice sheets that are challenging to model but could substantially increase sea level rise.
Under the most extreme emissions scenario we considered, we could not rule out rapid ice sheet loss leading to sea level rise approaching 2 meters (7 feet) by the end of this century.
Fortunately, if the world limits warming to well below 2 C, it should take many centuries for sea level rise to exceed 2 meters – a far more manageable situation.
Are the oceans or ice nearing any tipping points?
“Tipping point” is a vague term used in many different ways by different people. The IPCC defines tipping points as “critical thresholds beyond which a system reorganizes, in a way that is very fast or irreversible” – for example, a temperature rise beyond which climate dynamics commit an ice sheet to massive loss.
Because the term is so vague, the IPCC generally focuses on characteristics of changes in a system – for example, whether a system might change abruptly or irreversibly – rather than whether it fits the strict dynamic definition of a “tipping point.”
One example of a system that might undergo abrupt changes is the large-scale pattern of ocean circulation known as the Atlantic Meridional Overturning Circulation, or AMOC, of which the Gulf Stream is part. Paleoclimate evidence tells us that AMOC has changed rapidly in the past, and we expect that AMOC will weaken over this century. If AMOC were to collapse, it would make Europe warm more slowly, increase sea level rise along the U.S. Atlantic coast, and shift storm tracks and monsoons. However, most evidence indicates that such a collapse will not happen in this century.
There is mixed evidence for abrupt changes in the polar ice sheets, but clear evidence that changes in the ice sheets can be locked in for centuries and millennia.
If the world succeeds in limiting warming to 1.5 C (2.7 F), we expect to see about 2-3 meters (7-10 feet) of sea level rise over the next 2,000 years; if the planet continues to warm and reaches a 5 C (9 F) increase, we expect to see about 20 meters (70 feet) over the next 2,000 years.
Some people also discuss summer Arctic sea ice – which has undergone substantial declines over the last 40 years and is now smaller than at any time in the past millennium – as a system with a “tipping point.” However, the science is pretty clear that there is no critical threshold in this system. Rather, summer Arctic sea ice area decreases roughly in proportion to the increase in global temperature, and if temperature were stabilized, we would expect sea ice area to stabilize also.
What do scientists know now about hurricanes that they didn’t realize when the last report was written?
Since the last IPCC assessment report in 2013, there has been increasing evidence that hurricanes have grown more intense, and intensified more rapidly, than they did 40 years ago. There’s also evidence that hurricanes in the U.S. are moving more slowly, leading to increased rainfall.
However, it’s not clear that this is due to the effects of greenhouse gases – reductions in particulate pollution have also had important effects.
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The clearest effect of global warming is that a warmer atmosphere holds more water, leading to more extreme rainfall, like that seen during Hurricane Harvey in 2017. Looking forward, we expect to see hurricane winds and hurricane rains continue to increase. It’s still unclear how the overall number of hurricanes will change.
The report involved 234 scientists, and then 195 governments had to agree on the summary for policymakers. Does that broad range of views affect the outcome?
When you’re writing a report like this, a key goal for the scientists is to accurately capture points of both scientific agreement and scientific disagreement.
For example, with respect to ice sheet changes, there are certain processes on which there is broad agreement and other processes where the science is still emerging and there are strong, discordant views. Yet knowing about these processes may be crucially important for decision-makers trying to manage risk.
That’s why, for example, we talk not only about most likely outcomes, but also about outcomes where the likelihood is low or as-yet unknown, but the potential impacts are large.
The IPCC uses a transparent process to produce its report – the authors have had to respond to over 50,000 review comments over the three years we’ve spent writing it. The governments also weigh in, having to approve every line of a concise Summary for Policy Makers that accurately reflects the underlying assessment – oftentimes making it clearer in the process.
I’m very pleased that, as with past reports, every participating government has signed off on a summary that accurately reports the current state of climate science.