APRIL 8, 2015
As the frozen Arctic soil known as “permafrost” thaws, it
could release a large amount of carbon — in the form of both carbon dioxide and
methane — to the atmosphere. And this
new source of greenhouse gas emissions could be large enough that it could
substantially undermine attempts to cut down on emissions from fossil fuels.
A new overview of what we know about the permafrost carbon
problem has just come out in Nature, written by a group of 17 experts on
the matter. In other words, this is probably the most thorough scientific look
at the issue yet. And the researchers, led by Edward Schuur of Northern
Arizona University, basically confirm that we have a serious problem on
our hands.
The bottom line is that the permafrost carbon problem
doesn’t look like it’s going to just go away as researchers better refine their
estimates. Rather, it’s something that the world, and especially its leaders
who are the ones making climate agreements, will have to deal with.
“Initial estimates of greenhouse gas release point towards
the potential for substantial emissions of carbon from permafrost in a warmer
world, but these could still be underestimates,” the study notes.
A much cited estimate from past literature is that northern
permafrost contains 1,700 gigatons of carbon — a gigaton is a billion metric
tons — which is a vast amount and around double what currently exists in the
atmosphere.
The new study goes back closely over past estimates in light
of new evidence, and comes to a broadly consistent conclusion. It finds that
there are between 1,330 and 1,580 gigatons of carbon in the top three meters of
global permafrost soil, in what are called yedomas (permafrost with
particularly high ice content), and in Arctic river deltas.
And then on top of that, it says, there is a possible 400
additional gigatons in “deep terrestrial permafrost sediments” — not to mention
a simply unknown amount in permafrost below the sea in shallow continental
shelves, such as beneath the East Siberian Sea.
Overall, it’s a troubling large amount of carbon —
especially in light of numbers presented by the U.N. Intergovernmental Panel on
Climate Change, suggesting that if we want to have a good chance of holding
global warming to 2 degrees Celsius above pre-industrial temperatures, we
probably have only about 500 more gigatons of carbon in total that we can emit.
“We’ve gone back with this whole synthesis effort, looked
through all the data, and synthesized, and yeah, this problem is not going
away,” says lead study author Schuur.
Fortunately, the new study also finds that any sudden or
catastrophic release of Arctic carbon stores is unlikely. Rather, the experts
estimate that by 2100, somewhere between 5 and 15 percent of the 1,330-1,580
gigatons could be emitted. Ten percent of the total would equate to
around 130 to 160 gigatons of carbon emitted this century — which is both good
news and bad news at the same time.
The good news is that the permafrost emissions are “unlikely
to occur at a speed that could cause abrupt climate change over a period of a
few years to a decade,” as the study puts it. The bad news, though, is that 160
gigatons, even though it’s less than we’re expected to emit from fossil fuels
in coming decades, is still a large enough amount to really matter for the
planet — especially given the relatively tight carbon budget that we have
remaining.
And it could, of course, be more. If you assume 15 percent
of the carbon will be emitted in this century, for instance, then the
range becomes about 200 to 237 gigatons. Moreover, the emissions don’t end
at 2100 — they continue well into the next century.
Much of the research that is synthesized in the
new Nature paper has been conducted since the last official report of
the United Nations’ Intergovernmental Panel on Climate Change — whose climate
projections didn’t include permafrost emissions. New models, perhaps, will —
and accordingly, may spit out results suggesting that reducing our emissions
enough to stave off the worst climate outcomes will be even harder than
previously thought.
“I think this highlights, there’s a big carbon cycle out
there that we’re influencing, but we don’t control the whole thing,” says
Schuur.