Arctic

Arctic will transform into greenhouse gas source by 2100

Thawing of Arctic permafrost will likely dump 68 billion extra tons of carbon into the air before 2100, giving global warming an unexpected jolt and transforming the Far North into one of the world's net sources for climate-changing greenhouse gases, according to a new study by an international team of scientists.

That amount of carbon equals about 7.5 years of emissions by every person on Earth at current rates — including all of the exhaust from all of the world's cars, semi-trucks, jets, ships, power plants and factories over the course of 2,737 days.

The study — which crunched reams of soil warming and climate change numbers through a French supercomputer — overturns the notion that a warmer, greener Arctic will absorb more carbon than it will spew from its new expanses of soggy peat

Any budding plant growth may just be a little too late, the study concludes.

"Including permafrost processes turns out to be very important," said lead author Charles Koven, with Berkeley Lab's Earth Sciences Division, in this story about the study. "Previous models tended to dramatically underestimate the amount of soil carbon at high latitudes because they lacked the processes of how carbon builds up in soil. Our model starts off with more carbon in the soil, so there is much more to lose with global warming."

The study — Permafrost carbon-climate feedbacks accelerate global warming — was published in August in the Proceedings of the National Academy of Sciences. Koven, a now new staffer with the federal Department of Energy's Lawrence Berkeley National Laboratory, worked on the project while he was a postdoctoral researcher at France's Laboratoire des Sciences du Climat et de l'Environnement. With the help of seven scientists from France, Canada, and the United Kingdom, Koven conjured the new estimates by running climate models through the supercomputer at France's Alternative Energies and Atomic Energy Commission.

The findings are among a growing body of work predicting that climate change will accelerate throughout the Arctic as natural processes feed on themselves to produce even more warming.

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The shrinking of summer sea ice exposes darker ocean water that absorbs more solar energy and in turn produces more melting and thinner ice in subsequent seasons. Warming induced storm patterns cycle evermore multi-year ice into the North Atlantic, leaving behind thinner and younger ice that becomes even vulnerable to summer melt. Unprecedented wildfires strip vegetation off tundra and expose permafrost to faster thawing — a process that ultimately triggers more of the same warm dry fire weather in future seasons.

And underlying it all are the greenhouse gases.

How Arctic’s role in global carbon drama has shifted

The natural presence of certain gases like carbon dioxide in the air helps keep the Earth warm enough for life to exist. Solar radiation warms the planet, and these gases slow the loss of that heat back into space. They act somewhat like glass in a greenhouse, hence the nickname.

The Earth's CO2 concentration has been rising over the past century, and most scientists blame the increase on the burning of fossil fuel by people. The Earth's CO2 level is now more than 389 parts per million — higher than any previous August on record, according to the latest measurements posted by the Mauna Loa Observatory in Hawaii.

Until recently, the Arctic wasn't seen as a potential major contributor to greenhouse gas concentrations. The 2007 report from the Intergovernmental Panel on Climate Change concluded that the Arctic probably would continue to absorb more carbon than it produced — but there were no guarantees.

"Although models project that Arctic terrestrial ecosystems and the active layer will be a small sink for carbon in the next century, processes are complex and uncertainty is high," the report stated here.

Since then, scientists have been discovering that the Arctic will almost certainly drift across the line from carbon storehouse to carbon source due to drier and warmer summer conditions. And it can happen fast.

A study published earlier this summer found that a single unprecedented wildfire that burned 400 square miles of Alaska's North Slope in 2007 spewed more carbon into the air in a few months than the entire Arctic normally produces in a year.

"Our results show how rapidly a single tundra fire — even one that burned relatively surficially — can offset local and biome-scale C uptake," the authors wrote. "At both local and regional scales, fire emissions of this magnitude can instantaneously offset or reverse C cycling processes hypothesized to feedback negatively to warming such as greening of the Arctic."

But it doesn't take something as cinematic as a wildfire. The slo-mo burn of rising summer temperatures and deeper thaw can produce the same result over many decades.

Eons of trapped carbon exposed

Trapped in the ground beneath the surface of the Arctic is an enormous store of carbon — thousands of years of dying plants and other organic material frozen in a sort of stases within permafrost. Most of this material never thaws enough to decay and start releasing its carbon into the air.

"Much of this carbon is presently trapped and not cycling," explains this story about the study. "But scientists believe that some of it could be released in response to warming and become a positive feedback to global climate change. At stake is an estimated 2,167 petagrams of carbon in all layers of high-latitude soil, which is more than two trillion U.S. tons."

University of Alaska Fairbanks permafrost expert Vladimir Romanovsky explains why climate warming and drying will trigger this change in this primer on permafrost dynamics

The IPCC predictions of 2007 assumed the tropics would produce carbon while mid-latitudes and high-latitude ecosystems would tend to store more carbon only because the climate models of the time didn't fully take into account just how much carbon was stored in the permafrost, noted Koven and his co-authors.

"We show here that including the vast permafrost carbon pool in models leads to a qualitatively different result, in which high latitudes act as future (carbon dioxide) and (methane), leaving only the mid latitudes as potential climate regulators," they concluded.

Firing up the supercomputer

To get the new results, the scientists tuned up a computer model that analyzes land surface ecosystems so that it accounted for the carbon cycle down inside the ground. In the Arctic, how fast soil carbon rots and how much greenhouse gas it produces depends on the temperature at the line between ground that seasonally thaws during summer and the permafrost that never thaws.

Here's the crux: this "freeze-thaw" boundary will sink deeper and deeper into the Earth as the Arctic heats up and the soil grows warmer — a dynamic that will expose evermore ancient carbon to decay as the years pass. More rot means a additional greenhouse gas gets spewed into the air.

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"To determine how these processes affect the balance of carbon dioxide and methane in high-latitude soils, the scientists ran four simulations from 1860 to 2100, each with a different assortment of processes," explained this story. "They added in a middle-of-the-road climate change scenario that caused high-latitude surface soil to rise 8 degrees Celsius by 2100, which is much greater than the global average."

The results? Depending on the simulation, thawing Arctic soils will send somewhere between 25 and 82 petagrams of additional carbon into the air before 2100. The best estimate — one that used all permafrost processes — predicted 62 petagrams, or about 68 billion U.S. tons.

For more research into Arctic permafrost, and a glimpse into its current health, check out the Permafrost Laboratory at UAF's Geophysical Institute.

Contact Doug O'Harra at doug(at)alaskadispatch.com.

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