(Skip Intro)
AGGI Details and Data

An Introduction to NOAA's Annual Greenhouse Gas Index


Earth

Long-lived greenhouse gases absorb infrared radiation and warm the atmosphere, land, and oceans. The contributions of different gases to that process varies greatly depending on the gas and how its concentration has changed over time, making it difficult to grasp how the heating by greenhouse gases has changed overall.

In 2006, scientists with NOAA’s Global Monitoring Laboratory developed the Annual Greenhouse Gas Index, or 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.

Plot of global average abundances of greenhouse gases
Global average abundances of 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.

These five gases currently account for about 95 percent of the sustained change in Earth’s energy balance arising from emissions of long-lived greenhouse gases since 1750. Eighteen additional (“secondary”) greenhouse gases are also tracked by NOAA scientists and are included in the AGGI, and they account for the remaining 5 percent.

aggi figure 3
The AGGI over time, as derived from NOAA’s measurements of 23 long-lived greenhouse gases since 1979. Prior to 1979, a range of sources were used to create this figure, including measurements of ambient air back to 1958 from C.D. Keeling, and measurements of air extracted from ice cores and consolidated snow collected in polar regions.

The index is benchmarked to a value of 1.0 for the year 1990, the baseline year for emission reductions in early global climate agreements. The AGGI in 2025 was 1.56, which means that the increment of heat added by long-lived greenhouse gases since the dawn of the industrial era has increased by 56% since 1990.

The AGGI continues to provide an easily understandable way to track the increasing amount of excess heat being trapped in the atmosphere by human-emitted greenhouse gases.

Key takeaways:

  • The AGGI in 2025 was 1.56, which means that the increment of heat added by long-lived greenhouse gases since the dawn of the industrial era has increased by 56% since 1990.
  • 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 35 years for it to increase by another 56%.
  • In terms of CO2 equivalents, the atmosphere in 2025 contained approximately 544 ppm of these gases, of which 425.6 ppm is CO2 alone. The rest comes from other gases.
  • CO2 is by far the largest contributor to the value of the AGGI and how it has changed over time.

More details on the 2025 Annual Greenhouse Gas Index are at gml.noaa.gov/aggi/aggi.html.