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Greenhouse gas pollution trapped 49% more heat in 2021 than in 1990

Greenhouse gas pollution caused by human activities trapped 49% more heat in the atmosphere last year than in 1990

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Greenhouse gas pollution caused by human activities trapped 49% more heat in the atmosphere last year than in 1990. The measurements are mainly based on very precise calculations of greenhouse gases in air samples collected around the world and the result contains little uncertainty, detailed the text.

Greenhouse gas pollution caused by human activities trapped 49% more heat in the atmosphere in 2021 than it did in 1990, according to NOAA scientists.

Greenhouse gas

In 2021, the AGGI reached a value of 1.49, meaning that man-made greenhouse gases trapped 49% more heat in the atmosphere than they did in 1990. Because it is based primarily on very precise measurements of greenhouse gases in air samples collected around the world, the result has little uncertainty.

CO2 is the primary concern because it remains in the atmosphere and oceans for thousands of years and is by far the largest contributor to global warming. This warming is directly related to the temperatures of the oceans, which largely determine the number and magnitude of tropical storms, and therefore, hurricanes. The AGGI is indexed to 1990, the reference year for the Kyoto Protocol and the year the IPCC's first Scientific Assessment of Climate Change was published.

"The AGGI tells us the rate at which we're driving global warming," said Ariel Stein, acting director of NOAA's Global Monitoring Laboratory (GML). “Our measurements show that the main gases responsible for climate change continue to increase rapidly, even as the damage caused by climate change becomes increasingly clear. The scientific conclusion that humans are responsible for its increase is irrefutable."

Carbon dioxide (CO2) is by far the most abundant greenhouse gas emitted by humans. Some 36 billion metric tons of CO2 are emitted each year from transportation, power generation, cement manufacturing, deforestation, agriculture, and many other practices.

A substantial fraction of the CO2 emitted today will persist in the atmosphere for more than 1,000 years. Not surprisingly, it is also the largest contributor to AGGI in terms of quantity and rate of increase.

NOAA measurements showed the global average concentration of CO2 in 2021 was 414.7 parts per million (ppm). The increase was 2.6 ppm during that year, about the average annual increase of the previous decade and much higher than the increase measured between 2000 and 2009.


One of the biggest scientific questions for climate scientists is what has been driving the sharp and sustained rise in methane (CH4) since 2006 since it is the second most important greenhouse gas.

Methane levels are currently about 162% higher than pre-industrial levels. From NOAA observations, scientists believe that the amount of methane emitted in 2021 was 15% higher than between 1984 and 2006.

Methane is the second most important greenhouse gas in warming the planet. The causes of its escalation since 2007 are not fully understood, but NOAA scientists conclude that changes in the isotopic composition of atmospheric methane overtime point to microbial sources - likely from wetlands, agriculture and landfills - as the driver.

"We should absolutely target man-made methane emissions, especially those from fossil fuels because it is technologically feasible to control them," said Xin Lan, a scientist at the Cooperative Institute for Research in Environmental Sciences (CIRES) who works at the Laboratory. NOAA's Global Monitoring Committee, before noting, "If wetlands are emitting more methane due to warming and changes in global precipitation caused by rising CO2 levels, that's something we can't control directly. And that would be very worrying."

Nitrous oxide

The third most important greenhouse gas is nitrous oxide (N2O), another long-lived pollutant that is increasing every year, but it is different because it is due to population expansion, not energy demand.

N2O pollution is primarily the result of the use of fertilizers to support agriculture and food production, especially for an expanding world population.

"We can find alternative energy sources to replace fossil fuels," stressed Stephen Montzka, a scientist at the Global Monitoring Laboratory who directs the AGGI report each year, and specified that "reducing emissions associated with food production is a very difficult task."

These three greenhouse gases (CO2, CH4, and N2O), plus two banned ozone-depleting chemicals, account for 96% of the excess heat trapped in the atmosphere due to human activity since 1750. The remaining 4% comes from 16 other greenhouse gases.

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