The U.S. National Oceanic & Atmospheric Administration publishes an Annual Greenhouse Gas Index (AGGI), “a measure of the warming influence of long-lived trace gases and how that influence is changing each year.” Thus, AGGI is an index that measures climate forcing associated with long-lived greenhouse gases. The Index would be an excellent resource for instructors who involve their students in climate negotiations exercises, as well as a potent reminder of how the promise of Paris is confronted by the practical reality of trends in radiative forcing and atmospheric concentrations of greenhouse gases.
Among the findings of the latest assessment:
- Carbon dioxide concentrations creased by an average of 1.76 ppm per year from 1979-2015. However, the trend has accelerated in recent years, averaging about 1.5 ppm per year in the 1980s and 1990s, 2.0 ppm per year during the last decade. Moreover, atmospheric carbon dioxide increased 3 ppm in the past year, for only the second time since 1979.
- Increases in carbon dioxide concentrations in the atmosphere has resulted in a whopping 50% increase in its direct warming influence on climate since 1990
- While methane concentrations remained constant in the atmosphere from 1999-2006 (after declining from 1983-1999), they have been increasing since 2007, due to factors such as increasing temperatures in the Arctic in 2007, increased precipitation in the tropics in 2007 and 2007; this trend accelerated between 2014-2015. Nitrous oxides concentrations have also accelerated in recent years.
- Radiative forcing from chloroflourocabons is in decline, primarily due to the Montreal Protocol on Substances that Deplete the Ozone Layer. The importance of this regime, designed to address threats to the ozone layer, in terms of climate change are clear: without the treaty, climate forcing would have been 0.3 watt m-2 greater, or approximately half of the increase in radiative forcing attributable to carbon dioxide since 1990;
- Radiative forcing of long-lived, well-mixed greenhouse gases increased 37% from 1990 (the Kyoto baseline year) to 2015, with carbon dioxide accounting for nearly 80% of this increase;
- Increases in greenhouse gas concentrations over the past 60 years have accounted for approximately 75% of the total increase in the Index in the past 260 years.
Among the questions for class discussion that this study’s findings might generate are:
- What impacts might purported fugitive methane releases associated with fracking be having on concentrations of atmospheric methane?
- What might the implications be of positive feedback mechanisms that might release substantial amounts of methane from ocean-based methane clathrates?
- Why are concentrations of carbon dioxide accelerating in recent years despite efforts at the national and international level to arrest greenhouse gas emissions?
