Always
in the future – never in the present!
Unexpected
Future Boost of Methane Possible from Arctic Permafrost
NASA,
18
August, 2018
New
NASA-funded research has discovered that Arctic permafrost’s
expected gradual thawing and the associated release of greenhouse
gases to the atmosphere may actually be sped up by instances of a
relatively little known process called abrupt thawing. Abrupt thawing
takes place under a certain type of Arctic lake, known as a
thermokarst lake that forms as permafrost thaws.
The
impact on the climate may mean an influx of permafrost-derived
methane into the atmosphere in the mid-21st century, which is not
currently accounted for in climate projections.
The
Arctic landscape stores one of the largest natural reservoirs of
organic carbon in the world in its frozen soils. But once thawed,
soil microbes in the permafrost can turn that carbon into the
greenhouse gases carbon dioxide and methane, which then enter into
the atmosphere and contribute to climate warming.
"The
mechanism of abrupt thaw and thermokarst lake formation matters a lot
for the permafrost-carbon feedback this century," said first
author Katey Walter Anthony at the University of Alaska, Fairbanks,
who led the project that was part of NASA’s Arctic-Boreal
Vulnerability Experiment (ABoVE), a ten-year program to understand
climate change effects on the Arctic. "We don’t have to wait
200 or 300 years to get these large releases of permafrost carbon.
Within my lifetime, my children’s lifetime, it should be ramping
up. It’s already happening but it’s not happening at a really
fast rate right now, but within a few decades, it should peak."
The
results were published in Nature
Communications.
Using
a combination of computer models and field measurements, Walter
Anthony and an international team of U.S. and German researchers
found that abrupt thawing more than doubles previous estimates of
permafrost-derived greenhouse warming. They found that the abrupt
thaw process increases the release of ancient carbon stored in the
soil 125 to 190 percent compared to gradual thawing alone. What's
more, they found that in future warming scenarios defined by the
Intergovernmental Panel on Climate Change, abrupt thawing was as
important under the moderate reduction of emissions scenario as it
was under the extreme business-as-usual scenario. This means that
even in the scenario where humans reduced their global carbon
emissions, large methane releases from abrupt thawing are still
likely to occur.
Permafrost
is ground that is frozen year-round. In the Arctic, ice-rich
permafrost soils can be up to 260 feet (80 meters) thick. Due to
human-caused warming of the atmosphere from greenhouse gas emissions,
a gradual thawing of the permafrost is currently taking place where
the upper layer of seasonally thawed soil is gradually getting
thicker and reaching deeper into the ground. This process wakes up
microbes in the soil that decompose soil organic matter and as a
result release carbon dioxide and methane back into the atmosphere.
This gradual thaw process is accounted for in climate models and is
thought to have minimal effect as thawed ground also stimulates the
growth of plants, which counterbalance the carbon released into the
atmosphere by consuming it during photosynthesis.
However,
in the presence of thermokarst lakes, permafrost thaws deeper and
more quickly. Thermokarst lakes form when substantial amounts of ice
in the deep soil melts to liquid water. Because the same amount of
ice takes up more volume than water, the land surface slumps and
subsides, creating a small depression that then fills with water from
rain, snow melt and ground ice melt. The water in the lakes speeds up
the thawing of the frozen soil along their shores and expands the
lake size and depth at a much faster pace than gradual thawing.
"Within
decades you can get very deep thaw-holes, meters to tens of meters of
vertical thaw," Walter Anthony said. "So you’re flash
thawing the permafrost under these lakes. And we have very easily
measured ancient greenhouse gases coming out."
These
ancient greenhouse gases, produced from microbes chewing through
ancient carbon stored in the soil, range from 2,000 to 43,000 years
old. Walter Anthony and her colleagues captured methane bubbling out
of 72 locations in 11 thermokarst lakes in Alaska and Siberia to
measure the amount of gas released from the permafrost below the
lakes, as well as used radiocarbon dating on captured samples to
determine their age. They compared the emissions from lakes to five
locations where gradual thawing occurs. In addition, they used the
field measurements to evaluate how well their model simulated the
natural field conditions.
Methane
bubbles up from the thawed permafrost at the bottom of the
thermokarst lake through the ice at its surface.
Credits:
Katey Walter Anthony/ University of Alaska Fairbanks
Team
members with the Alfred Wegener Institute (AWI) for Polar and Marine
Research in Germany then used U.S. Geological Survey-NASA Landsat
satellite imagery from 1999 to 2014 to determine the speed of lake
expansion across a large region of Alaska. From this data they were
able to estimate the amount of permafrost converted to thawed soil in
lake bottoms.
"While
lake change has been studied for many regions, the understanding that
lake loss and lake gain have a very different outcome for carbon
fluxes is new," said co-author Guido Grosse of AWI. "Over a
few decades, thermokarst lake growth releases substantially more
carbon than lake loss can lock in permafrost again [when the lake
bottoms refreeze]."
Because
the thermokarst lakes are relatively small and scattered throughout
the Arctic landscapes, computer models of their behavior are not
currently incorporated into global climate models. However, Walter
Anthony believes including them in future models is important for
understanding the role of permafrost in the global carbon budget.
Human fossil fuel emissions are the number one source of greenhouse
gases to the atmosphere, and in comparison, methane emissions from
thawing permafrost make up only one percent of the global methane
budget, Walter Anthony said. "But by the middle to end of the
century the permafrost-carbon feedback should be about equivalent to
the second strongest anthropogenic source of greenhouse gases, which
is land use change," she said.
To
learn more about ABoVE, visit: https://above.nasa.gov/
Meanwhile, this is the current reality - TODAY
Look at the emisions over the ESAS today
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