Greenhouse gas levels have hit yet another record – here’s why

Home » Greenhouse gas levels have hit yet another record – here’s why
Greenhouse gas levels have hit yet another record – here’s why


Carbon dioxide, methane and nitrous oxide reached record-high concentrations in the atmosphere in 2021, including the largest recorded increase in methane



Environment



26 October 2022

Greenhouse gas emissions are still rising

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Carbon dioxide, nitrous oxide and methane reached record high concentrations in the atmosphere in 2021 and have continued to rise through 2022.

Researchers at the World Meteorological Organization (WMO), a UN agency that has published an annual greenhouse gas bulletin since 2006, measured atmospheric concentrations of the key greenhouse gases at more than 100 monitoring sites around the world.

They found atmospheric carbon dioxide, responsible for about 66 per cent of global warming since 1750, increased on average by 2.5 parts per million to 415.5 parts per million in 2021. Nitrous oxide, responsible for about 7 per cent of warming, increased by 1.3 parts per billion to 334.5 parts per billion. These increases were slightly higher than the average year-to-year increase over the previous decade.

Methane, responsible for about 16 per cent of warming, saw the largest single-year increase since researchers started keeping records 40 years ago. Between 2020 and 2021, atmospheric methane increased by 18 parts per billion to reach 1908 parts per billion, more than two and half times pre-industrial levels.

“The continuing rise in concentrations of the main heat-trapping gases, including the record acceleration in methane levels, shows that we are heading in the wrong direction,” Petteri Taalas, Secretary-General of the WMO, said in a press release.

Steps to reduce methane emissions should be taken “without delay”, but reducing carbon dioxide emissions remains the top priority to avoid the worst effects of climate change, said Taalas.

What is causing the record levels?

It is no mystery about what is behind the rise in carbon dioxide and nitrous oxide. The increase in carbon dioxide is mainly from the continued burning of fossil fuels and cement production. The rise in nitrous oxide is primarily from nitrogen fertiliser, burning fossil fuels and several industrial processes. Significant natural sources of nitrous oxide include microbes in soil and the ocean.

But since methane concentrations started rising in 2007, researchers have struggled to explain why.

The largest anthropogenic sources of methane are livestock, oil and gas production and waste rotting in landfills; 60 per cent of atmospheric methane comes from anthropogenic sources like these. But there are also significant natural sources of methane, such as wetlands. The fact that these sources often are overlapping – e.g., a dairy farm near a wetland – as well as a lack of data, make it difficult to distinguish precisely what is behind the rise.

According to the WMO, the ratio of different carbon isotopes in atmospheric methane suggests a biological source. Models of how methane is transported around the atmosphere further narrow this down, suggesting that tropical wetlands could be to blame, with the increase in emissions possibly due to warmer temperatures and changing precipitation. However, the WMO says the role of that climate feedback remains uncertain.

Changes that affect how methane breaks down in the atmosphere might also contribute, though not enough to explain the rise. The authors of the report write it will take more modelling and careful monitoring to crack the methane mystery.

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