A dramatic increase in the amount of methane, a powerful greenhouse gas, that has occurred over the past 16 years might be an indicator that a “termination event”, where the planetary climate flips from its current cool interglacial state to a hotter, more tropical one, could occur within a matter of decades, according to a new study.
Previous naturally-occurring climate shifts such as this—referred to as “termination events” due to their tendency to put an end to ice ages—have been recorded in the gases trapped in ice cores over the past 800,000 years, and have been found to take just a handful of decades to unfold.
“A termination is a major reorganization of the Earth’s climate system,” explained study lead and professor emeritus of Earth sciences at Royal Holloway, University of London Euan Nisbet. “These repeated changes have taken the world from ice ages into the sort of interglacial we have now.”
These events typically follow three phases as they occur: the first is the gradual rise in atmospheric greenhouse gases, such as methane and carbon dioxide, resulting in a climate that becomes increasingly warmer over the span of a few thousand years; the next phase is the termination event itself, a sharp spike in atmospheric methane that is accompanied by a corresponding jump in global temperatures; the third phase is an Earth with a climate much warmer than we are familiar with, hot enough for the Arctic to be home to tropical grasslands.
“Within the termination, which takes thousands of years, there’s this abrupt phase, which only takes a few decades,” Nisbet said. “During that abrupt phase, the methane soars up and it’s probably driven by tropical wetlands.”
Methane (CH4) is a powerful greenhouse gas, capable of retaining up to 86 times more heat energy than the same mass of carbon dioxide over a 20-year period. Outgassing of this methane contributes to the buildup of greenhouse gases in the atmosphere, in turn increasing global warming that melts more Arctic permafrost, that in turn releases more methane—an unfortunate feedback loop that adds to the effects of rising atmospheric carbon dioxide concentrations.
In 2006, climate researchers began recording a sudden increase in atmospheric methane levels that didn’t correspond to human-based output, despite human activities such as agriculture and fossil fuel use being responsible for about 60 percent of modern CH4 emissions; by 2013 they discovered that the rise in CH4 levels was accelerating, and in 2020 they realized that the rise was outpacing anything known in the natural record.
“It looks as if there’s a big, new methane source turning on,” Nisbet said.
In recent years this source was found to be increased outgassing from tropical wetlands, particularly ones found in Africa, due to a “significant change” in tropical weather brought about by human-caused climate change: the increase in temperature has resulted in an increase in the extent of the range of these wetlands, increasing the amount of plants growing in the region, and more plants means that more methane is released when they die and decompose.
Although the study’s findings aren’t proof that a termination event is imminent, its authors point out that whenever these conditions have occurred in the past a climate flip was not far behind. “The closest analogy we have to what we think is happening today is these terminations,” Nisbet remarked.
“We’re not saying we’ve got proof this is happening, but we’re raising the question.”
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