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.