1. The Annual Greenhouse Gas Index (AGGI) is a measure of the capacity of Earth’s atmosphere to trap heat as a result of the presence of long-lived greenhouse gases. The AGGI provides standardized information about how human activity has affected the climate system through greenhouse gas emissions.
2. This indicator demonstrates that the warming influence of greenhouse gases in the atmosphere has increased substantially over the last several decades. In 2017, the AGGI was 1.42, an increase of more than 40% since 1990.
3. The AGGI can inform decisions about mitigation strategies.
Full Summary:
Radiative forcing (shown on the left vertical axis) is the change in the amount of solar radiation, or energy from the sun, that is trapped by the atmosphere and remains near Earth. When radiative forcing is greater than zero, it has a warming effect; when it is less than zero, it has a cooling effect. In this indicator, radiative forcing from long-lived greenhouse gases is shown relative to the year 1750. The AGGI (shown on the right vertical axis) is an index of radiative forcing normalized to the year 1990; it shows how the warming influence of greenhouse gases in the atmosphere has increased since that year.
This indicator demonstrates the change in radiative forcing resulting from changing concentrations of the following greenhouse gases: carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), chlorofluorocarbons (CFC-11 and CFC-12), and a set of 15 minor, long-lived halogenated gases. The National Oceanic and Atmospheric Administration (NOAA) Global Monitoring Division provides high-precision measurements of the abundance and distribution of long-lived greenhouse gases that are used to calculate global average concentrations. Radiative forcing for each gas is computed from these concentrations, and total radiative forcing for all gases is used to calculate the AGGI.
The AGGI shows that the warming influence of long-lived greenhouse gases in the atmosphere increased by 42% between 1990 and 2017. Carbon dioxide is currently the largest contributor to radiative forcing. Radiative forcing from methane has steadily increased since 2007, after having been nearly constant from 1999 to 2006. Owing to the Montreal Protocol, an international agreement signed in 1987, CFCs have been decreasing since the mid- to late 1990s after a long period of increase. However, CFC replacements (many of the “other halogenated gases” in the graph) have been increasing since the phase-out of CFCs.
Fundamentally, the AGGI is a measure of what human activity has already done to affect the climate system through greenhouse gas emissions. It provides quantitative information in a simplified, standardized format that decision makers can use to inform mitigation strategies.
Low flows on the Colorado River in Cataract Canyon. Flows on the Colorado have always risen and fallen seasonally, but water managers in the west now firmly see a future with less water overall to work with.
The phrase “climate change” did not appear on the agenda of a recent three-day meeting of the Colorado Water Congress, but the topic was often front and center at the conference, as it increasingly is at water meetings around the state and the region.
Amy Haas, the new executive director of the Upper Colorado River Commission, told the Water Congress audience of about 300 water managers, irrigators, engineers and lawyers that “hydrology is changing more rapidly than we once thought” and that “it is primarily due to climate change.”
And, Haas said, attitudes among water managers about climate change are changing too.
“I feel that water managers are not only talking about climate change, they are talking about it frequently,” she said. “This is the new reality that we have to contend with. And I’m encouraged to hear the discussion, openly, in all sorts of water management forums.”
Haas also recognized Brad Udall, who was also at Water Congress, in her remarks.
A senior climate researcher and scientist at Colorado State University, Udall continues to get the attention of water managers with studies that tie rising temperatures to declining river levels.
Udall recently published a paper, along with Mu Xiao and Dennis Lettermaier, on the declining flows of the Colorado River.
The paper found that flows in the upper Colorado River basin declined by 16.5 percent from 1916 to 2014, while annual precipitation increased only slightly, by 1.4 percent.
By conducting experiments with a model that uses temperature and precipitation as inputs, the researchers found that “53% of the decreasing runoff trend is associated with unprecedented basin-wide warming, which has reduced snowpack and increased plant water use,” Udall explained. “The remaining 47% of the trend is associated mostly with reduced winter precipitation in four highly productive sub-basins, all located in Colorado.”
Climate Science 101
Udall is also using “aridification” at water meetings to describe what’s happening in the Colorado River basin, and he’s offered up a succinct summary of his research on climate change, on a t-shirt, that says “it’s warming, it’s us, expert agree, it’s bad, (and) we can fix it.”
Andy Mueller, the general manager of the Colorado River District, also makes no bones about climate change.
He told the Water Congress audience that the River District is “planning for a future with less water, and it being a permanent situation.”
And on Sept. 14, at a River District seminar in Grand Junction, Mueller told an audience of over 250 water managers, users and stakeholders that science shows that “climate change is going to reduce the natural flow into Lake Powell by 20 percent by 2035 and by the end of the century, 35 percent.”
Mueller added, “We’ve got to recognize that we have a supply problem in the upper basin.”
Past not relevant
Jim Lochhead, the CEO and manager of Denver Water, said during his remarks at the Colorado Water Congress meeting that the impact of climate change goes even beyond supply issues.
“A warming climate is something we’ve built into our scenario planning process, but it’s not just a water supply concern,” Lochhead said, also citing wildfires and the resulting runoff into reservoirs and rivers, and the increased cost for water treatment from “warmer water” and “emerging contaminates.”
He also said Denver Water no longer thinks that the past is a reliable guide to the future, citing the “over-assumptions of water supply” in interstate compacts like the 1922 Colorado River Compact, the state’s water rights system which is based on “past hydrology,” and state and federal regulations that are based on “past water temperatures and water quality parameters.”
“Those are all geared to the past and not to the future,” Lochhead said.
Denver Water has also “abandoned linear water-supply planning,” where, as he put it, “you look at the past hydrology, look at past population trends, and project those out into the future, look at a water supply gap, and then go out and find water to meet that gap.”
“That no longer can meet the challenges that we face today,” Lochhead said.
And Lochhead said that “firm yield,” the capacity of a given water supply system to meet demands in a dry spell, and the Holy Grail for water providers, was now an outmoded concept.
“We don’t use that term any more, actually, because we know that no yield is firm,” he said.
And if that wasn’t riveting enough for water managers to hear, Lochhead also said that “as we look at the warming climate some of the scenarios in our scenario planning are actually pretty scary, and they will be coming at us more and more quickly.”
From the Associated Press via The Grand Junction Daily Sentinel:
The National Park Service says unsafe levels of a type of algae that can be harmful to humans have been found in the water of a central Colorado reservoir.
Park officials said they detected the presence of toxins that can be produced by algae blooms in water samples taken from Blue Mesa Reservoir.
The agency advised visitors to avoid contact with shallow waters in an area known as the Iola Basin and to avoid mats of algae throughout the reservoir.
The reservoir is part of Curecanti National Recreation Area west of Gunnison, Colorado.
Harmful blue-green algae is natural to the area but can spread quickly in warm, shallow water.
