NOAA index tracks the continuing increase in heating from greenhouse gases
2025-12-22
Greenhouse gases associated with human activity trapped 54 percent more heat in the atmosphere during 2024 than those same gases did in 1990, according to an annual NOAA report.
Long-lived greenhouse gases absorb infrared radiation and warm the atmosphere, land, and oceans. NOAA’s Annual Greenhouse Gas Index, known as the AGGI, tracks increases in the warming influence of heat-trapping gases—including carbon dioxide, methane, nitrous oxide, chlorofluorocarbons, and 15 other gases—generated by human activity.
In 2006, scientists in the Global Monitoring Laboratory (GML) developed the AGGI as a way to help non-scientists readily appreciate how the overall warming from atmospheric concentrations of these greenhouse gases has changed over time.
The index is based on thousands of air samples collected each year from NOAA’s Global Greenhouse Gas Reference Network and analyzed at GML in Boulder, Colorado.
The AGGI is benchmarked to a value of 1.0 for the year 1990, the baseline year for Kyoto Protocol emission reductions. In 2024, the AGGI stood at a value of 1.54. That means that the human contribution to warming from long-lived greenhouse gases in the atmosphere in 2024 was 54% higher than in 1990.
“The AGGI continues to provide an easily understandable way to track the increasing amount of heat being trapped in the atmosphere by greenhouse gases,” said Stephen Montzka, GML’s senior scientist.
Global average abundances measured by GML of the five major long-lived greenhouse gases: carbon dioxide, methane, nitrous oxide, CFC-12 and CFC-11.
The five long-lived greenhouse gases that contribute most to the AGGI include carbon dioxide, methane, nitrous oxide, and two ozone-depleting gases, CFC-12 and CFC-11.
Carbon dioxide remains by far the largest contributor to total forcing from these gases, with methane the second largest contributor. Together, all five gases currently account for about 96 percent of the sustained change in Earth’s energy balance arising from emissions of long-lived greenhouse gases since 1750. Seventeen additional (“secondary”) greenhouse gases are also tracked by NOAA scientists and are included in the AGGI—they account for the remaining 4 percent.
It took approximately 240 years for the value of the AGGI to go from 0 to 1—that is, to increase from preindustrial values to that in 1990—and only 34 years for it to increase by another 54%.
More details on the NOAA Annual Greenhouse Gas Index are at gml.noaa.gov/aggi/.