Natural methane emissions are accelerating and at levels not seen in paleoclimate records

While human activity contributes to the amount of heat-trapping methane in the atmosphere, methane from natural sources such as swamps is accerlating and could trigger rapid global heating within decades.While human activity contributes to the amount of heat-trapping methane in the atmosphere, methane from natural sources such as swamps is accerlating and could trigger rapid global heating within decades. (Photo: Siggy Nowak from Pixabay)

Of the most concerning greenhouse gases heating Earth far beyond natural variability, methane is nefarious. It is exponentially more potent than carbon dioxide at trapping heat, and its accelerated accumulation in the atmosphere could trigger unimaginable global heating within a few decades.

Methane may only last in the atmosphere for about a decade, but it is emitted each year naturally and from human activity like fossil fuel extraction and agriculture. Humans now are responsible for about three-fifths of methane emissions, but since 2006 the increase and acceleration now has been attributed to natural sources, according to research led by Euan Nisbet, Professor of Earth Sciences at Royal Holloway University of London.

The accelerated growth of atmospheric methane (CH4) since 2006 and further acceleration in the 2020s.

The accelerated growth of atmospheric methane (CH4) since 2006 and further acceleration in the 2020s. (Graph: Modified from Lan et al. (2022). Data from https://gml.noaa.gov/dv/data.html)

Such sudden increases in methane emissions coincided with transitions from past ice ages to the warm interglacial climates such as the one we’re enjoying today. But the recent surge in methane emissions is troubling in multiple ways:

  • Today’s methane levels of nearly 1.9 parts per million (ppm) far exceed the 0.7 ppm of pre-industrial times.
  • Accelerated levels since 2006 increased in 2011, and further accelerated during the 2020s.
  • As our warming planet holds more moisture in the atmosphere, rainfall increases, and wetlands expand.
  • Expanding wetlands resulting from warmer global temperatures release more methane into the atmosphere.

The ocean is another natural source of methane, but the Nisbet-led research traced the rising levels primarily to a vast network of meandering rivers and swamps in East Africa, with tropical swamps in South America another area of concern.

Methane bubbles up from the ocean floor off the coast of Oregon. In deep water, microbes oxidize methane into carbon dioxide, which increases ocean acidifcation. Methane seepage in shallow water can reach the atmosphere and further heat the planet.

Methane bubbles up from the ocean floor off the coast of Oregon. In deep water, microbes oxidize methane into carbon dioxide, which increases ocean acidifcation. Methane seepage in shallow water can reach the atmosphere and further heat the planet. (Photo: Oregon State University)

Reducing the unnatural sources of methane

Methane leaks from oil and gas facilities and is responsible for about a third of warming temperatures since pre-industrial times, and reducing methane is in the spotlight at this year’s COP28 climate conference. There the U.S. on Dec. 2 joined several other countries in pledging to significantly reduce methane emissions by 2038.

Among the famous pledges resulting from annual COP “Convention of Parties” meetings is the 2015 Paris Agreement pledge to limit rising global temperatures to 1.5 degrees Celsius above pre-industrial levels. But Earth breached that milepost on about a third of days just this year, ensuring 2023 will be the hottest on record. In fact, global scorching is well ahead of schedule.

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