Annual Greenhouse Gas Index

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.
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.

Warming influence of greenhouse gases is increasing

The warming influence of
greenhouse gases Gases that absorb heat in the atmosphere near the Earth's surface, preventing it from escaping into space. If the atmospheric concentrations of these gases rise, the average temperature of the lower atmosphere will gradually increase, a phenomenon known as the greenhouse effect. Greenhouse gases include, for example, carbon dioxide, water vapor, and methane.
in the atmosphere has increased substantially over the last several decades. In 2017, the AGGI was 1.42, which represents an increase of more than 40% since 1990. Carbon dioxide remains the largest contributor to radiative forcing.
Radiative forcing The change in energy flux (expressed in Watts/square meter) at the tropopause or top of the atmosphere due to a change in a climate driver (such as changes in atmospheric carbon dioxide concentrations).
(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 (represented by a red dot); it shows that the warming influence of long-lived greenhouse gases in the atmosphere increased by 42% between 1990 and 2017.

About Annual Greenhouse Gas Index

This
indicator An observation or calculation that allows scientists, analysts, decision makers, and others to track environmental trends, understand key factors that influence the environment, and identify effects on ecosystems and society.
demonstrates the change in radiative forcing resulting from changing concentrations of twenty greenhouse gases:
  • carbon dioxide (CO₂)
  • methane (CH₄)
  • nitrous oxide (N₂O)
  • chlorofluorocarbons (CFC-11 and CFC-12)
  • a set of 15 minor, long-lived halogenated gases
This indicator measures the average total radiative forcing of 20 long-lived greenhouse gases, including carbon dioxide, methane, and nitrous oxide. The results were calculated by the National Oceanic and Atmospheric Administration (NOAA) based on measured concentrations of the gases in the atmosphere, compared with the concentrations that were present around 1750, before the Industrial Revolution began. Because each gas has a different ability to absorb and emit energy, this indicator converts the changes in greenhouse gas concentrations into a measure of the total radiative forcing (warming effect) caused by each gas. Radiative forcing is calculated in watts per square meter, which represents the size of the energy imbalance in the atmosphere. Learn more about radiative forcing.

NOAA’s 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.

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.
Why It's Important
  • The warming influence of greenhouse gases in the atmosphere has increased substantially over the last several decades.
  • AGGI is a measure of what human activity has already done to affect the climate system through greenhouse gas emissions.
  • Decision makers can use this indicator to inform
    mitigation Measures to reduce the amount and speed of future climate change by reducing emissions of heat-trapping gases or removing carbon dioxide from the atmosphere.
    strategies.