In the remote northern Arctic, greenhouse gas emissions risk coming up through icy cracks. Flying over some of the most inaccessible parts of Alaska and northwestern Canada, NASA researchers have detected a shocking amount of thawing in permafrost, the frozen layer of ground that covers much of the region.
A systematic review published in the journal Geophysical Research Letters it gives us no escape. If this tundra melts, it will release gases from millions of sources of methane and other carbon emissions into the atmosphere, further accelerating global warming.
Today we know that the Arctic is heating up twice as fast as anywhere else on Earth, but given how cold and formidable the landscape is, we still don't know where more methane is emitted.
We consider areas that show an excess of 3.000 parts per million methane in the sensing space between our airborne sensor and the ground to be hotspots. And in the observed area we detected 2 million of these hotspots.
Clayton Elder, NASA's Jet Propulsion Laboratory.
Does this sound a lot more than you imagined? It is true. For many months of the year, much of the Arctic is inaccessible to scientists, so ground-based observations have so far covered only a fraction of the region. NASA researchers see this new technology as a breakthrough, giving us a completely new perspective on the region. And it alarms us quite a bit.
Sources of methane in the Arctic, the detection technique
Using a single infrared spectrometer (known as AVIRIS-NG), the researchers collected over 400 sets of data. The flights were made in the months of July and August 2017, covering approximately 30.000 square kilometers of Arctic land (12.000 square miles). In total, the trips have collected approx a billion careful observations of methane emissions and the results reveal a clear dispersion pattern centered on water.
“AVIRIS-NG has been used in previous methane surveys. Those polls had focused on man-made emissions in populated areas and with important infrastructure already known to produce emissions", he claims Elder. “In our study, for the first time the tool was used to find hotspots in areas where there is no intense human activity.”
On average these spots are clustered along the shores of lakes, ponds, streams and other wetland features, usually within 30-40 metres. From there on, the hotspots begin to fade, becoming rarer as they move further away from the water, until, finally, they almost disappear completely, about 300 meters away.
What are the causes?
The authors are still unclear as to why this phenomenon occurs. Previous research has indicated that some Arctic lakes, known as thermokarsts, can not only emit bubbles that release methane, but they can also melt the permafrost around them even faster.
Instead of centimeters of thaw, as for terrestrial environments, in the past 60 years we have seen 15 meters of thaw under newly formed lakes in the Goldstream Valley.
The factors of this further melting near wetlands and water bodies are still unknown, but there are several hypotheses on the merit.
One of these, the most accepted at the moment, is that methane sources could be clustered around waterways as these facilitate the spread of plants. A sort of chain effect: the carbon frozen for thousands of years melts, becomes food for microbes that transform everything into methane, and the phenomenon accelerates. The flatter areas of the Arctic were 'green' areas and are therefore more subject to the phenomenon.
Whatever the reason, it is clear that we need more research in the field. The masses of water (or recent Arctic islands which emerged precisely because of the thaw) seem like a good starting point. Methane has a global warming potential about 30 times greater than carbon dioxide. Even if the Paris Agreement is met, Arctic permafrost is expected to shrink by another 45%, unleashing these methane sources and releasing billions more tons of carbon and methane into the atmosphere.
