11 July 2017 (NOAA) – 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. [cf. Graph of the Day: NOAA annual greenhouse gas index (AGGI), 1700-2015 ]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.Scientists who created the AGGI assigned a value of zero to the year 1750. Analysis of air trapped in ice and snow in Antarctica by NOAA and others demonstrate that after this date, atmospheric carbon dioxide concentrations departed from a relatively stable 280 parts per million observed during the previous 10,000 years, climbing to 403 parts per million by the end of 2016. An AGGI value of 1.0 was assigned to the year 1990, the baseline year of the Kyoto Protocol, an international treaty calling for the reduction in greenhouse gas emissions. In 2016, the AGGI rose to a value of 1.4.

NOAA’s greenhouse gas index up 40 percent since 1990

11 July 2017 (NOAA) – […] Weekly data are used to create a smoothed north-south latitude profile from which a global average is calculated. The atmospheric abundance of CO2 has increased by an average of 1.80 ppm per year over the past 38 years (1979-2016). The CO2 increase is accelerating: it averaged about 1.5 ppm per year in the 1980s and 1990s, and it was 2.2 ppm per year during the last decade (2007-2016). The annual CO2 increase from 1 Jan 2016 to 1 Jan 2017 was 2.9 ± 0.1 ppm (see https://www.esrl.noaa.gov/gmd/ccgg/trends/global.html), which is the second largest increase observed in the measurement record since 1980; the largest increase was measured during 2015.The growth rate of methane declined from 1983 until 1999, consistent with an approach to steady-state, assuming no trend in CH4lifetime. Superimposed on this decline is significant interannual variability in growth rates [Dlugokencky et al., 1998, 2003]. From 1999 to 2006, the atmospheric CH4 burden was about constant, but since 2007, globally averaged CH4 has been increasing again. Causes for the increase during 2007-2008 included warm temperatures in the Arctic in 2007 and increased precipitation in the tropics in 2007 and 2008 [Dlugokencky et al., 2009], and isotopic measurements argue for continued increasing microbial emissions after 2008 (e.g., from wetlands or agriculture) [Schaefer et al., 2016; Nisbet et al., 2016]. Recent papers have also suggested contributions to the plateau and subsequent increase in methane’s global abundance from changes in the loss rate of methane [Rigby et al., 2017]. Since 2013, the global within-year increase (1 Jan to 1 Jan) in methane has become even larger, with increases between 8.7 and 12.6 ppb/yr through 2016 compared to an average annual increase of 5.7 ± 1.2 ppb yr-1 between 2007 and 2013 (https://www.esrl.noaa.gov/gmd/ccgg/trends_ch4/). The atmospheric burden of nitrous oxide continues to slowly increase over time, with an average rate of 0.9 ppb yr-1 over the past decade. Radiative forcing from the sum of observed CFC changes ceased increasing in about 2000 and continued to decline through 2016 [Montzka et al., 2011]. The latter is a response to decreased emissions related to the fully adjusted and amended Montreal Protocol on Substances that Deplete the Ozone Layer. […]

2016 Results

[…] Of the five long-lived greenhouse gases that contribute 96% to radiative climate forcing, CO2 and N2O are the only ones that continue to increase at a regular rate. Radiative forcing from CH4 increased from 2007 to 2016 after remaining nearly constant from 1999 to 2006. While the radiative forcing of the long-lived, well-mixed greenhouse gases increased 39.9% from 1990 to 2016 (by ~0.86 watts m-2), CO2 has accounted for about 80% of this increase (~0.69 watts m-2). Had the ozone-depleting gases not been regulated by the Montreal Protocol and its amendments, it is estimated that climate forcing would have been as much as 0.3 watt m-2 greater in 2010 [Velders et al., 2007], or more than half of the increase in radiative forcing due to CO2 alone since 1990. The recent Kigali Amendment to the Montreal Protocol controls future production of HFCs, which are substitutes for CFCs and other ozone-depleting gases, to ensure that radiative forcing for these substitutes does not increase substantially in the future. Of the ozone-depleting gases and their substitutes, the largest contributors to direct warming in 2016 were CFC-12, followed by CFC-11, HCFC-22, CFC-113 and HCFC-134a. Although the concentration of HCFC-22 in the remote atmosphere surpassed that of CFC-11 by the end of 2015 (Figure 2), the radiative forcing arising from HCFC-22 is still only 80% of that from CFC-11 because CFC-11 is more efficient at trapping infrared radiation on a per molecule basis.An Annual Greenhouse Gas Index (AGGI) has been defined as the ratio of the total direct radiative forcing due to long-lived greenhouse gases for any year for which adequate global measurements exist to that which was present in 1990. 1990 was chosen because it is the baseline year for the Kyoto Protocol. This index, shown with the direct radiative forcing values in Table 2 and on the right-hand axis of Figure 4, is a measure of the interannual changes in conditions that affect carbon dioxide emission and uptake, methane and nitrous oxide sources and sinks, the decline in the atmospheric abundance of ozone-depleting chemicals related to the Montreal Protocol, and the increase in their substitutes (HCFCs and HFCs). Most of this increase is related to CO2. For 2016, the AGGI was 1.40 (representing an increase in total direct radiative forcing of 40% since 1990). The increase in CO2 forcing alone since 1990 was nearly 54% (see Fig. 3). The decline in the CFCs has tempered the increase in net radiative forcing. The AGGI will be updated each spring when air samples from all over the globe for the previous year have been obtained and analyzed. [more]