The Drivers of Climate Change -- Tracking Global Greenhouse Gas Trends and their Warming Influence

Of the National Physical Climate Indicators, two stand out as primary drivers of climate change – the Global Monthly Average of Carbon Dioxide Concentration and the Annual Greenhouse Gas Index. Both of these are products of high quality, long-term, globally distributed monitoring of greenhouse gases in the atmosphere. To support monitoring of the trends of these gases over decades, NOAA maintains the WMO World Calibration Scales for the major contributors to radiative forcing and its own universally accepted scales for most of the minor greenhouse gases. Maintenance of these scales over time ensures the consistency of measurements from decade to decade. Further quality control through use of internal and external comparisons of on-going measurements places tight constraints on spatial and temporal bias.

By far the most influential greenhouse gas contributing to radiative forcing is carbon dioxide (CO2). Its amount at Mauna Loa is reported on-line daily and its global trend updated monthly on NOAA’s global monitoring website and at climate.gov. This is one of the most closely watched records of atmospheric composition, as its accelerating rate of increase is a constant reminder that society has yet to deal successfully with its emissions of this gas. Much of CO2 emitted remains in the atmosphere for 1000s of years, which is why it is of substantial concern. But atmospheric CO2 is not alone in warming the planet and driving climate change. Many other gases contribute in a lesser way to this long-term trend and are captured along with CO2 in NOAA’s Annual Greenhouse Gas Index (AGGI). The AGGI is a normalized compilation of the radiative forcing (RF) of five major long-lived greenhouse gases (96% of RF) and 15 minor gases (4% of RF). Because it does not include short lived gases (< ~10 years), it measures a robust RF trend that represents the warming influence society has already committed itself to living in. This presentation discusses the development of these two indexes and their national and global use.