Greenhouse gas pollution caused by human activities trapped 49% more heat in the atmosphere in 2021 than in 1990, according to NOAA scientists.
NOAA’s annual greenhouse gas index, known as the AGGI, tracks the increasing warming influence of human emissions of heat-trapping gases, including carbon dioxide, methane, nitrous oxide, chlorofluorocarbons and 16 other chemicals. AGGI converts complex scientific calculations of how much additional heat these gases capture into a single number that can easily be compared to previous years and tracks the rate of change.
This graph illustrates the relative contributions of major greenhouse gas pollutants to global warming, in watts per square meter along the left axis. The NOAA Annual Greenhouse Gas Index (AGGI) is shown on the right axis. Credit: NOAA Global Monitoring Laboratory
The AGGI is indexed to 1990, the reference year for the Kyoto Protocol and the year of publication of the IPCC’s first scientific assessment on climate change.
“AGGI tells us how fast we’re driving global warming,” said Ariel Stein, acting director of NOAA’s Global Monitoring Laboratory (GML). “Our measurements show that the main gases responsible for climate change continue to increase rapidly, even as the damage caused by climate change becomes increasingly clear. The scientific conclusion that humans are responsible for their increase is irrefutable.
In 2021, the AGGI reached a value of 1.49, which means that human-emitted greenhouse gases have trapped 49% more heat in the atmosphere than in 1990. Because it is based primarily on very precise measurements of greenhouse gases in air samples taken around the world. , the result contains little uncertainty.
Global average abundances of the major well-mixed, long-lived greenhouse gases – carbon dioxide, methane, nitrous oxide, CFC-12 and CFC-11 – from NOAA’s Global Air Sampling Network since the beginning of 1979 are represented here. These five gases account for about 96% of the direct radiative forcing by long-lived greenhouse gases since 1750. The remaining 4% is contributed by 15 other halogen gases, including HCFC-22 and HFC-134a, to which NOAA observations are also presented here. . Credit: NOAA Global Monitoring Laboratory
The biggest culprit
Carbon dioxide or CO2, is by far the most abundant human-emitted greenhouse gas. About 36 billion metric tons of CO2 are emitted each year from transportation, power generation, cement manufacturing, deforestation, agriculture, and many other practices. A substantial fraction of CO2 emitted today will persist in the atmosphere for more than 1,000 years. Unsurprisingly, it is also the largest contributor to AGGI in terms of amount and rate of increase.
NOAA measurements showed the global average concentration of CO2 in 2021 was 414.7 parts per million (ppm). The annual increase was 2.6 ppm during that year, about the average annual increase of the previous decade, and well above the increase measured during the period 2000-2009. CO2 levels have increased by 61 ppm since 1990, which is 80% of the increase in heat tracked by AGGI since that year.
“CO2 is the biggest contributor because it stays in the atmosphere and oceans for thousands of years and is by far the biggest contributor to global warming,” said GML Senior Scientist Pieter Tans. “Eliminate CO2 pollution must be at the center of all efforts to deal with climate change.
This graph shows the increasing warming influence over time of CO2 and non-CO2 greenhouse gases, in CO2 equivalents, on the left axis. The corresponding increase in AGGI is shown on the right axis. Credit: NOAA Global Monitoring Laboratory.
Methane: does global warming feed global warming?
One of the most important scientific questions for climate scientists is what has caused the sharp and sustained increase in the second most important greenhouse gas – methane – since 2006.
Levels of atmospheric methane, or CH4, averaged 1,895.7 parts per billion in 2021. The 16.9 ppb increase recorded for 2021 was the fastest seen since the early 1980s, when a more stringent measurement regime was initiated . Methane levels are currently about 162% higher than pre-industrial levels. Based on NOAA observations, scientists estimate that the amount of methane emitted in 2021 was 15% higher than the period 1984-2006.
Methane is the second most important greenhouse gas in global warming. The warming influence of CH4 since the pre-industrial era is about a quarter of that of CO2. The causes of the dramatic increase after 2007 are not fully understood, but NOAA scientists have concluded that changes in the isotopic composition of atmospheric methane over time indicate that microbial sources, likely wetlands, of the ‘agriculture and landfills, are the main driver. Fossil fuel emissions, they suggest, made a lesser contribution.
“We definitely need to target man-made methane emissions – especially those from fossil fuels – because it is technologically possible to control them,” said Xin Lan, a CIRES scientist working at the Global Monitoring Lab. “If wetlands emit more methane due to warming and changes in global precipitation caused by increased CO2 levels, that’s something we can’t directly control. And that would be very worrying.
No laughing matter
The third most important greenhouse gas is one you may have encountered during anesthesia in the dentist’s chair. Nitrous oxide, or N2O, is another long-lived climate-forcing pollutant primarily emitted by humans. It increases every year. But it’s different in that it’s driven by expanding populations, not energy demand. NOT2O pollution is primarily the result of the use of fertilizers to support agriculture and food production, especially for a growing world population.
“We can find alternative energy sources to replace fossil fuels,” said Stephen Montzka, the GML scientist who leads the AGGI report each year, “but reducing the emissions associated with food production is a very difficult task.” .
These three greenhouse gases, plus two banned ozone-depleting chemicals, account for about 96% of the excess heat trapped in the atmosphere due to human activity since 1750. The remaining 4% comes from 16 other greenhouse gases also monitored by the AGGI. In total, they trapped an amount of heat equivalent to 508 ppm of CO2 in 2021.
A figure to monitor the impact of man on the climate
NOAA scientists published the first AGGI in 2006 to help policymakers, educators and the public understand the cumulative impact of greenhouse gases on climate over time.
Scientists compared AGGI to the year 1750, the start of the Industrial Revolution, assigning it a value of zero. An AGGI value of 1.0 was assigned to 1990.
The AGGI is based on thousands of air samples taken from sites around the world each year from NOAA Global Greenhouse Gas Reference Network. Concentrations of these greenhouse gases and other chemicals are determined by analysis of these samples at NOAA’s Global Monitoring Laboratory in Boulder, Colorado. Scientists then calculate how much additional heat is trapped in the Earth system by these gases and how much that has changed over time to understand the contribution of human activity.
For more information, contact Theo Stein, NOAA Communications, at [email protected].