The quantity of methane leaking from the frozen soil during the long Arctic winters is probably much greater than climate models estimate, scientists have found.
They say at least half of annual methane emissions occur in the cold months from September to May, and that drier, upland tundra can emit more methane than wetlands.
The multinational team, led by San Diego State University (SDSU) in the US and including colleagues from the National Oceanic and Atmospheric Administration, and the University of Sheffield and the Open University in the UK, have published their conclusion, which challenges critical assumptions in current global climate models, in the Proceedings of the National Academy of Sciences.
Methane, a potent greenhouse gas, is about 25 times more powerful per molecule than carbon dioxide over a century, but more than 84 times over 20 years. The methane in the Arctic tundra comes primarily from organic matter trapped in soil which thaws seasonally and is decomposed by microbes.
It seeps naturally from the soil over the course of the year, but climate change can warm the soil enough to release more methane from organic matter that is currently stable in the permafrost.
Scientists have for some years been accurately measuring Arctic methane emissions and incorporating the results into their climate models. But crucially, the SDSU team says, almost all of these measurements have been obtained during the Arctic’s short summer.
Its long cold period has been largely “overlooked and ignored,” according to Walter Oechel of SDSU, with most researchers thinking that, because the ground is frozen solid during the cold months, methane emissions practically shut down for the winter.
“Virtually all the climate models assume there’s no or very little emission of methane when the ground is frozen,” he says. “That assumption is incorrect.”
The authors say the water trapped in the soil doesn’t freeze completely at 0°C. The top layer of the ground – known as the active layer – thaws in the summer and refreezes in the winter, and it experiences a kind of sandwiching effect as it freezes.
When temperatures are around 0°C (called “the zero curtain”) the top and bottom of the active layer begin to freeze, but the middle remains insulated. Micro-organisms in this unfrozen layer continue to break down organic matter and emit methane many months into the Arctic winter.
Dual Approach
To find out how much methane is emitted during the winter, the researchers used both ground-based and airborne methods.
The ground-based researchers recorded methane emissions from five sampling towers in Alaska over two summer-autumn-winter cycles between June 2013 and January 2015 and found that a major part of winter emissions was recorded when temperatures hovered near the zero curtain.
“This is extremely relevant for the Arctic ecosystem, as the zero curtain period continues from September until the end of December, lasting as long as or longer than the entire summer season,” said Donatella Zona, the study’s lead author.
“These results are the opposite of what modellers have been assuming, which is that the majority of the methane emissions occur during the warm summer months while the cold-season methane contribution is nearly zero.”
Data Confirmed
The researchers also found that during the cold season methane emissions were higher at the drier, upland tundra sites than in the wetlands. Upland tundra had previously been assumed to contribute a negligible amount of methane, Zona said.
To test whether the site-specific sampling was typical of methane emissions across the Arctic, the researchers compared their results with measurements recorded during flights made by NASA’s Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE).
The data from the ground-based sites proved well-matched with the larger-scale aircraft measurements, which showed that large areas of Arctic tundra and boreal forest continued to emit high levels of methane to the atmosphere long after the surface soil had frozen.
The team also used satellite microwave sensor measurements to develop regional maps of surface water cover, including the timing, extent and duration of seasonal flooding and drying of the region’s wetlands. This showed that the big methane-emitting areas were in the drier tundra.
Truthout Is Preparing to Meet Trump’s Agenda With Resistance at Every Turn
Dear Truthout Community,
If you feel rage, despondency, confusion and deep fear today, you are not alone. We’re feeling it too. We are heartsick. Facing down Trump’s fascist agenda, we are desperately worried about the most vulnerable people among us, including our loved ones and everyone in the Truthout community, and our minds are racing a million miles a minute to try to map out all that needs to be done.
We must give ourselves space to grieve and feel our fear, feel our rage, and keep in the forefront of our mind the stark truth that millions of real human lives are on the line. And simultaneously, we’ve got to get to work, take stock of our resources, and prepare to throw ourselves full force into the movement.
Journalism is a linchpin of that movement. Even as we are reeling, we’re summoning up all the energy we can to face down what’s coming, because we know that one of the sharpest weapons against fascism is publishing the truth.
There are many terrifying planks to the Trump agenda, and we plan to devote ourselves to reporting thoroughly on each one and, crucially, covering the movements resisting them. We also recognize that Trump is a dire threat to journalism itself, and that we must take this seriously from the outset.
Last week, the four of us sat down to have some hard but necessary conversations about Truthout under a Trump presidency. How would we defend our publication from an avalanche of far right lawsuits that seek to bankrupt us? How would we keep our reporters safe if they need to cover outbreaks of political violence, or if they are targeted by authorities? How will we urgently produce the practical analysis, tools and movement coverage that you need right now — breaking through our normal routines to meet a terrifying moment in ways that best serve you?
It will be a tough, scary four years to produce social justice-driven journalism. We need to deliver news, strategy, liberatory ideas, tools and movement-sparking solutions with a force that we never have had to before. And at the same time, we desperately need to protect our ability to do so.
We know this is such a painful moment and donations may understandably be the last thing on your mind. But we must ask for your support, which is needed in a new and urgent way.
We promise we will kick into an even higher gear to give you truthful news that cuts against the disinformation and vitriol and hate and violence. We promise to publish analyses that will serve the needs of the movements we all rely on to survive the next four years, and even build for the future. We promise to be responsive, to recognize you as members of our community with a vital stake and voice in this work.
Please dig deep if you can, but a donation of any amount will be a truly meaningful and tangible action in this cataclysmic historical moment. We are presently looking for 201 new monthly donors in the next 24 hours.
We’re with you. Let’s do all we can to move forward together.
With love, rage, and solidarity,
Maya, Negin, Saima, and Ziggy