NOAA’s Annual Greenhouse Gas Index, which tracks the warming influence of long-lived greenhouse gases, has increased by 40 percent from 1990 to 2016 — with most of that attributable to rising carbon dioxide levels, according to NOAA climate scientists.

The role of greenhouse gases on influencing global temperatures is well understood by scientists, but it’s a complicated topic that can be difficult to communicate. In 2006, NOAA scientists introduced the Annual Greenhouse Gas Index as a way to help policymakers, educators and the public understand changes in the direct climate warming influence exerted by greenhouse gas levels over time.

“The greenhouse gas index is based on atmospheric data, so it’s telling us what is happening to Earth’s climate right now,” said James Butler, director of NOAA’s Global Monitoring Division.

NOAA bases the AGGI on precise measurements of long-lived atmospheric gases in samples collected from a network of sites around the globe. The index is proportional to the change in the direct warming influence exerted by long-lived greenhouse gases since 1750, which is the accepted date for onset of the industrial revolution.

The five primary gases tracked by the AGGI are carbon dioxide, methane, nitrous oxide, and two chlorofluorocarbons that were banned 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. Fifteen secondary greenhouse gases also tracked by the AGGI account for the remaining 4 percent.