Indicator : indicator-annual-greenhouse-gas-index-2020

Indicator: Annual Greenhouse Gas Index

2020 indicator

Key Points: The warming influence of greenhouse gases in the atmosphere has increased substantially over the last several decades. In 2019, the AGGI was 1.45, which represents an increase of 45% since 1990. Carbon dioxide remains the largest contributor to radiative forcing. About the Indicator: This indicator 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. 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 strategies.

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