NOAA’s Annual Greenhouse Gas Index ticks up another notch

May 30, 2018

The warming influence from long-lived greenhouse gases rose again in 2017, reflecting ongoing changes to the atmosphere associated predominantly with human activities, NOAA scientists announced today.

NOAA's Barrow Atmospheric Baseline Observatory is one of more than 50 sites around the world where NOAA and partners collect air samples for high precision analysis. These data are used to measure the direct warming influence of greenhouse gases on the climate.

NOAA’s Annual Greenhouse Gas Index is designed to track the change in the atmosphere’s ability to absorb heat since the onset of the industrial revolution. It is based on air samples collected from a network of sites around the globe and analyzed at NOAA’s Earth System Research Lab in Boulder, Colorado. 

Scientists assigned an AGGI value of 1.0 to the year 1990, which was the baseline year of the Kyoto Protocol, an international treaty calling for the reduction in greenhouse gas emissions. In 2016, the AGGI registered 1.40, reflecting a 40 percent increase in the climate-warming influence of greenhouse gases in the atmosphere since 1990. In 2017, the AGGI rose to a value of 1.41.

“Greenhouse gases trap heat – it’s that simple,” said James Butler, director of NOAA’s Global Monitoring Division. “The AGGI is a single number that shows how much extra heat the atmosphere is able to trap every year.”

The five primary gases tracked by the AGGI are carbon dioxide, methane, nitrous oxide, and two chlorofluorocarbons that are strictly controlled by the Montreal Protocol because they damage Earth’s protective ozone layer. These five primary greenhouse gases account for about 96 percent of the increased climate-warming influence since 1750, which is the accepted date for the onset of the industrial revolution. Fifteen secondary greenhouse gases also tracked by the AGGI account for the remaining 4 percent. 

Carbon dioxide is the most important greenhouse gas

Of the five primary gases tracked by the AGGI, carbon dioxide, or CO2, is by far the most important in both total amount and rate of increase. It is responsible for 80 percent of the increased warming influence captured by the AGGI since 1990.

Globally averaged annual concentrations of carbon dioxide rose from 354 parts per million in 1990 to 405, or 14 percent, in just 27 years. Since 1750, the concentration of carbon dioxide in the atmosphere has risen 46 percent. 

NOAA scientists introduced the Annual Greenhouse Gas Index in 2006 as a way to help policymakers, educators, and the public understand the influence exerted by greenhouse gas levels over time. The AGGI is updated each spring when air samples from all over the globe for the previous year have been obtained and analyzed.


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