NOAA’s greenhouse gas index up 40 percent since 1990

Desdemona Despair

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.Carbon dioxide is most important greenhouse gas

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

The amount of CO₂ in the atmosphere grew by 2.9 parts per million (ppm) in 2016, roughly equal to the record rise observed in 2015. During calendar year 2016, the global average for CO₂ was approximately 403 parts per million, which represents a 45-percent increase since the start of the industrial era.

In April 2017, CO₂ levels on Mauna Loa averaged 409 ppm.

The direct warming influence exerted by all five primary and 15 secondary gases measured by the AGGI are equivalent to the warming influence of 489 ppm of CO₂.One of many climate change indicators

The Greenhouse Gas Index is one of numerous indicators tracked by NOAA that demonstrate how the Earth’s climate is changing, including:

• The year 2016 was the third year in a row that a new global average temperature record was set, and the fifth time since 2000. Each of the first eight months of 2016  set record high temperatures for that month.

• All 16 years of the 21st century rank among the 17 warmest years on record.

• Last year was also the second-warmest year on record for the contiguous United States. Every state was warmer than average.

• During 2016, the globally-averaged sea surface temperature was also the highest in the 1880–2016 record, surpassing the previous record set in 2015.

• Maximum Arctic sea ice extent for the 2016-2017 winter season nearly set a record low for the third straight year. Arctic sea ice extent has decreased in all months and virtually all regions since scientists began tracking it by satellite in the late 1970s. Antarctic sea ice extent last year was the second smallest on record, behind 1986.

“We know that rising greenhouse gas emissions are continuing to trap more and more of the sun’s heat in the Earth system,” Butler said.

Access the complete AGGI for 2016 online at https://esrl.noaa.gov/gmd/aggi/aggi.html.

NOAA’s greenhouse gas index up 40 percent since 1990

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]

The NOAA Annual Greenhouse Gas Index (AGGI)