The NOAA Annual Greenhouse Gas Index (AGGI), 1700-2017. Pre-1978 changes in the CO2-equivalent concentration and AGGI based on the ongoing measurements of all greenhouse gases reported here, measurements of CO2 going back to the 1950s from C.D. Keeling [Keeling et al., 1958], and atmospheric changes derived from air trapped in ice and snow above glaciers [Machida et al., 1995, Battle et al., 1996, Etheridge, et al., 1996; Butler, et al., 1999]. Equivalent CO2 atmospheric amounts (in ppm) are derived with the relationship (Table 1) between CO2 concentrations and radiative forcing from all long-lived greenhouse gases. Graphic: NOAA

30 May 2018 (NOAA) – NOAA’s Annual Greenhouse Gas Index (AGGI), which tracks the warming influence of long-lived greenhouse gases, has increased by 41 percent from 1990 to 2017, up 1 percent from 2016 -- with most of that attributable to rising carbon dioxide levels, according to NOAA climate scientists. [cf. NOAA’s greenhouse gas index up 40 percent since 1990 – Carbon dioxide increase is accelerating and Graph of the Day: NOAA annual greenhouse gas index (AGGI), 1700-2015. –Des]

The greenhouse gas index is based on precise measurements of gases in the atmosphere, which are collected from a network of sites around the globe and analyzed at NOAA’s Earth System Research Lab in Boulder, Colorado. The index is proportional to the change in the direct climate-warming influence (also known as climate forcing) exerted by five primary greenhouse gases since the onset of the industrial revolution.

“The greenhouse gas index is based on highly accurate measurements and long-established principles of physics, so it tells us how we are raising the amount of heat trapped in the atmosphere right now,” said James Butler, director of NOAA’s Global Monitoring Division.

NOAA scientists introduced the Annual Greenhouse Gas Index in 2006 as a way to help policymakers, educators and the public understand the influence exerted by greenhouse gas levels over time. Called the AGGI for short, it is updated each spring when air samples from all over the globe for the previous year have been obtained and analyzed.

Five primary greenhouse gases are tracked by AGGI

The index tracks five primary gases: 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, marking the onset of the industrial revolution. 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 354 parts per million in 1990 and 405 parts per million by the end of 2017. Since 1750, the concentration of carbon dioxide in the atmosphere has risen 46 percent.

In April 2018, CO2 levels at NOAA’s Mauna Loa baseline atmospheric observatory averaged 410 ppm.

An AGGI value of 1.0 was assigned to the year 1990, which was the baseline year of the Kyoto Protocol, an international treaty calling for the reduction in greenhouse gas emissions. In 2016 the AGGI was 1.40, in 2017, the AGGI rose to a value of 1.41.

Carbon dioxide is the most important greenhouse gas

Carbon dioxide, or CO2, is by far the most important greenhouse gas in both total amount and rate of increase, and is responsible for 80 percent of the increased warming influence captured by the AGGI since 1990.

During 2017, NOAA’s Global Greenhouse Gas Reference Network Measurements showed that concentrations of CO2 in the atmosphere rose by 2.3 parts per million, following record increases of 2.9 ppm in 2016 and 2015. This is the sixth consecutive year CO2 rose by 2 ppm or more. Prior to 2012, back-to-back annual increases of 2 ppm or greater occurred only twice.

The direct warming influence exerted by all five primary and 15 secondary gases measured by the AGGI are equivalent to the warming influence of 493 ppm of CO2.

One of many climate change indicators

The Greenhouse Gas Index is one of numerous indicators tracked by NOAA during 2017 that demonstrate how the Earth’s climate is warming:

  • The globally averaged annual temperature during 2017 was third-warmest in NOAA's 138-year global temperature record, behind 2016 and 2015.

  • Each of the five of the warmest years have occurred since 2010. Each of the 10 warmest years have occurred in the past 20 years. All 18 years of the 21st Century rank among the 19 warmest on record. 

  • Record warmth was observed across parts of the western and central Pacific Ocean, western Indian Ocean, southern South America, and the southwestern contiguous U.S. and scattered across parts of the northern Atlantic Ocean, Africa, the Middle East, and eastern Asia.

  • For the contiguous U.S., 2017 was also the third warmest year since that data began to be recorded in 1895, coming in behind 2012 and 2016. It was the 21st consecutive warmer-than-average year for the U.S.

  • The five warmest years on record for the contiguous U.S. have all occurred since 2006.

  • For the third consecutive year, every one of the contiguous U.S. and Alaska had an above-average annual temperature.

  • During 2017, Texas experienced its warmest winter on record, California and Nevada experienced the warmest summer in 123 years, while Arizona, New Mexico, Maine, New Hampshire, Massachusetts, and Connecticut all experienced the highest average fall temperatures on record.

  • During 2017, the maximum extent of Arctic sea ice set a record low for the third straight year.

“Greenhouse gases trap heat – it’s that simple,” Butler said. “The AGGI is a single number that shows how much extra heat the atmosphere is able to trap every year.”

Access the complete AGGI for 2017 online.

NOAA’s greenhouse gas index up 41 percent since 1990

Global average abundances of the major, well-mixed, long-lived greenhouse gases - carbon dioxide, methane, nitrous oxide, CFC-12 and CFC-11 - from the NOAA global air sampling network, 1979-2017. These five gases account for about 96 percent of the direct radiative forcing by long-lived greenhouse gases since 1750. The remaining 4 percent is contributed by an assortment of 15 minor halogenated gases including HCFC-22 and HFC-134a, for which NOAA observations are also shown in the figure. Methane data before 1983 are annual averages from D. Etheridge [Etheridge et al., 1998], adjusted to the NOAA calibration scale [Dlugokencky et al., 2005]. Graphic: NOAA

30 May 2018 (NOAA) – […] Weekly data are used to create a smoothed north-south latitude profile from which a global average is calculated (Figure 2). The atmospheric abundance of CO2 has increased by an average of 1.81 ppm per year over the past 39 years (1979-2017). The CO2 increase is accelerating — while it averaged about 1.6 ppm per year in the 1980s and 1.5 ppm per year in the 1990s, the growth rate increased to 2.2 ppm per year during the last decade (2008-2017). The annual CO2 increase from 1 Jan 2017 to 1 Jan 2018 was 2.3 ± 0.1 ppm (see, which is lower than the previous two years, but higher than the average of the previous decade, and much higher than the two decades before that.

The growth rate of methane declined from 1983 until 1999, consistent with an approach to steady-state, assuming no trend in CH4 lifetime. 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 nearly 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 during 2007 and 2008 [Dlugokencky et al., 2009]. Isotopic measurements argue for continued increasing microbial emissions after 2008 (e.g., likey from wetlands or agriculture) [Schaefer et al., 2016; Nisbet et al., 2016]. Some 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 8.8 ± 2.6 through 2017 compared to an average annual increase of 5.7 ± 1.1 ppb yr-1 between 2007 and 2013 ( 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 2017 [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. […]

2017 Results

Figure 4 shows radiative forcing for the major gases and a set of 15 minor long-lived halogenated gases (CFC-113, CCl4, CH3CCl3, HCFCs 22, 141b and 142b, HFCs 134a, 152a, 23, 143a, and 125, SF6, and halons 1211, 1301 and 2402). Except for the HFCs and SF6, which do not contain chlorine or bromine, these gases are also ozone-depleting gases and are regulated by the Montreal Protocol. As expected, CO2 dominates the total forcing with methane and the CFCs becoming relatively smaller contributors to the total forcing over time. The five major greenhouse gases account for about 96% of the direct radiative forcing by long-lived greenhouse gas increases since 1750. The 15 minor halogenated gases contribute The remaining 4%.

Of the five long-lived greenhouse gases, CO2 and N2O are the only ones that continue to increase at regular rates over decades. Radiative forcing from CH4 increased since 2007 after remaining nearly constant from 1999 to 2006. While the radiative forcing of the long-lived, well-mixed greenhouse gases increased 41% from 1990 to 2017 (by ~0.90 watts m-2), CO2 has accounted for about 80% of this increase (~0.72 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 2017 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 84% of that from CFC-11 because CFC-11 is more efficient at trapping infrared radiation on a per molecule basis. [more]

The NOAA Annual Greenhouse Gas Index (AGGI)



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