What we know about permafrost melt is less than what we don’t know about it. So how do we determine the permafrost contribution to climate change?

WHO: E. A. G. Schuur, S. M. Natali, C. Schädel, University of Florida, Gainesville, FL, USA
B. W. Abbott, F. S. Chapin III, G. Grosse, J. B. Jones, C. L. Ping, V. E. Romanovsky, K. M. Walter Anthony University of Alaska Fairbanks, Fairbanks, AK, USA
W. B. Bowden, University of Vermont, Burlington, VT, USA
V. Brovkin, T. Kleinen, Max Planck Institute for Meteorology, Hamburg, Germany
P. Camill, Bowdoin College, Brunswick, ME, USA
J. G. Canadell, Global Carbon Project CSIRO Marine and Atmospheric Research, Canberra, Australia
J. P. Chanton, Florida State University, Tallahassee, FL, USA
T. R. Christensen, Lund University, Lund, Sweden
P. Ciais, LSCE, CEA-CNRS-UVSQ, Gif-sur-Yvette, France
B. T. Crosby, Idaho State University, Pocatello, ID, USA
C. I. Czimczik, University of California, Irvine, CA, USA
J. Harden, US Geological Survey, Menlo Park, CA, USA
D. J. Hayes, M. P.Waldrop, Oak Ridge National Laboratory, Oak Ridge, TN, USA
G. Hugelius, P. Kuhry, A. B. K. Sannel, Stockholm University, Stockholm, Sweden
J. D. Jastrow, Argonne National Laboratory, Argonne, IL, USA
C. D. Koven, W. J. Riley, Z. M. Subin, Lawrence Berkeley National Lab, Berkeley, CA, USA
G. Krinner, CNRS/UJF-Grenoble 1, LGGE, Grenoble, France
D. M. Lawrence, National Center for Atmospheric Research, Boulder, CO, USA
A. D. McGuire, U.S. Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska, Fairbanks, AK, USA
J. A. O’Donnell, Arctic Network, National Park Service, Fairbanks, AK, USA
A. Rinke, Alfred Wegener Institute, Potsdam, Germany
K. Schaefer, National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
J. Sky, University of Oxford, Oxford, UK
C. Tarnocai, AgriFoods, Ottawa, ON, Canada
M. R. Turetsky, University of Guelph, Guelph, ON, Canada
K. P. Wickland, U.S. Geological Survey, Boulder, CO, USA
C. J. Wilson, Los Alamos National Laboratory, Los Alamos, NM, USA
 S. A. Zimov, North-East Scientific Station, Cherskii, Siberia

WHAT: Interviewing and averaging the best estimates by world experts on how much permafrost in the Arctic is likely to melt and how much that will contribute to climate change.

WHEN: 26 March 2013

WHERE: Climactic Change, Vol. 117, Issue 1-2, March 2013

TITLE: Expert assessment of vulnerability of permafrost carbon to climate change (open access!)

We are all told that you should never judge a book by its cover, however I’ll freely admit that I chose to read this paper because the headline in Nature Climate Change was ‘Pandora’s Freezer’ and I just love a clever play on words.

So what’s the deal with permafrost and climate change? Permafrost is the solid, permanently frozen dirt/mud/sludge in the Arctic that often looks like cliffs of chocolate mousse when it’s melting. The fact that it’s melting is the problem, because when it melts, the carbon gets disturbed and moved around and released into the atmosphere.

Releasing ancient carbon into the atmosphere is what humans have been doing at an ever greater rate since we worked out that fossilised carbon makes a really efficient energy source, so when the Arctic starts doing that as well, it’s adding to the limited remaining carbon budget our atmosphere has left. Which means melting permafrost has consequences for how much time humanity has left to wean ourselves off our destructive fossil fuel addiction.

 How much time do we have? How much carbon is in those cliffs of chocolate mousse? We’re not sure. And that’s a big problem. Estimates in recent research think there could be as much as 1,700 billion tonnes of carbon stored in permafrost in the Arctic, which is much higher than earlier estimates from research in the 1990s.

To give that very large number some context, 1,700 billion tonnes can also be called 1,700 Gigatonnes, which should ring a bell for anyone who read Bill McKibben’s Rolling Stone global warming math article. The article stated that the best current estimate for humanity to have a shot at keeping global average temperatures below a 2^oC increase is a carbon budget of 565Gt. So if all the permafrost melted, we’ve blown that budget twice.

What this paper did, was ask the above long list of experts on soil, carbon in soil, permafrost and Arctic research three questions over three different time scales.

1. How much permafrost is likely to degrade (aka quantitative estimates of surface permafrost degradation)
2. How much carbon it will likely release
3. How much methane it will likely release

They included the methane question because methane has short term ramifications for the atmosphere. Methane ‘only’ stays in the atmosphere for around 100 years (compared to carbon dioxide’s 1000 plus years) and it has 33 times the global warming potential (GWP) of CO₂ over a 100 year period. So for the first hundred years after you’ve released it, one tonne of methane is as bad as 33 tonnes of CO₂. This could quickly blow our carbon budgets as we head merrily past 400 parts per million of CO₂ in the atmosphere from human forcing.

The time periods for each question were; by 2040 with 1.5-2.5^oC Arctic temperature rise (the Arctic warms faster than lower latitudes), by 2100 with between 2.0-7.5^oC temperature rise (so from ‘we can possibly deal with this’ to ‘catastrophic climate change’), and by 2300 where temperatures are stable after 2100.

The estimates the experts gave were then screened for level of expertise (you don’t want to be asking an atmospheric specialist the soil questions!) and averaged to give an estimate range. For surface loss of permafrost under the highest warming scenario, the results were;

1. 9-16% loss by 2040
2. 48-63% loss by 2100
3. 67-80% loss by 2300

Ouch. If we don’t start doing something serious about reducing our carbon emissions soon, we could be blowing that carbon budget really quickly.

For how much carbon the highest warming scenario may release, the results were;

1. 19-45billion tonnes (Gt) CO₂ by 2040
2. 162-288Gt CO₂ by 2100
3. 381-616Gt CO₂ by 2300

Hmm. So if we don’t stop burning carbon by 2040, melting permafrost will have taken 45Gt of CO₂ out of our atmospheric carbon budget of 565Gt. Let’s hope we haven’t burned through the rest by then too.

However, if Arctic temperature rises were limited to 2^oC by 2100, the CO2 emissions would ‘only’ be;

1. 6-17Gt CO₂ by 2040
2. 41-80Gt CO₂ by 2100
3. 119-200Gt CO₂ by 2300

That’s about a third of the highest warming estimates, but still nothing to breathe a sigh of relief at given that the 2000-2010 average annual rate of fossil fuel burning was 7.9Gt per year. So even the low estimate has permafrost releasing more than two years worth of global emissions, meaning we’d have to stop burning carbon two years earlier.

When the researchers calculated the expected methane emissions, the estimates were low. However, when they calculated the CO₂ equivalent (CO₂e) for the methane (methane being 33 times more potent than CO₂ over 100 years), they got;

1. 29-60Gt CO₂e by 2040
2. 250-463Gt CO₂e by 2100
3. 572-1004Gt CO₂e by 2300

Thankfully, most of the carbon in the permafrost is expected to be released as the less potent carbon dioxide, but working out the balance between how much methane may be released into the atmosphere vs how much will be carbon dioxide is really crucial for working out global carbon budgets.

The other problem is that most climate models that look at permafrost contributions to climate change do it in a linear manner where increased temps lead directly to an increase in microbes and bacteria and the carbon is released. In reality, permafrost is much more dynamic and non-linear and therefore more unpredictable, which makes it a pain to put into models. It’s really difficult to predict abrupt thaw processes (as was seen over 98% of Greenland last summer) where ice wedges can melt and the ground could collapse irreversibly.

These kinds of non-linear processes (the really terrifying bit about climate change) made the news this week when it was reported that the Alaskan town of Newtok is likely to wash away by 2017, making the townspeople the first climate refugees from the USA.

The paper points out that one of the key limitations to knowing exactly what the permafrost is going to do is the lack of historical permafrost data. Permafrost is in really remote hard to get to places where people don’t live because the ground is permanently frozen. People haven’t been going to these places and taking samples unlike more populated areas that have lengthy and detailed climate records. But if you don’t know how much permafrost was historically there, you can’t tell how fast it’s melting.

The key point from this paper is that even though we’re not sure exactly how much permafrost will contribute to global carbon budgets and temperature rise, this uncertainty alone should not be enough to stall action on climate change.

Yes, there is uncertainty in exactly how badly climate change will affect the biosphere and everything that lives within it, but currently our options range from ‘uncomfortable and we may be able to adapt’ to ‘the next mass extinction’.

So while we’re working out exactly how far we’ve opened the Pandora’s Freezer of permafrost, let’s also stop burning carbon.