Some people worry about rising sea levels due to global warming. But that will happen slowly. I worry about tipping points.
The word “tipping point” should remind you of pushing on a glass of water. If you push it a little, and then stop, it’ll right itself: no harm done. But if you push it past a certain point, it starts tipping over. Then it’s hard to stop.
So, we need to study possible tipping points in the Earth’s climate system. Here’s a list of them:
• Tipping point, Azimuth Library.
Today I want to talk about one: melting permafrost. When melting permafrost in the Arctic starts releasing lots of carbon dioxide and methane—a vastly more potent greenhouse gas—the Earth will get even hotter. That, in turn, will melt even more permafrost. In theory, this feedback loop could tip the Earth over to a much hotter state. But how much should we worry about this?
Climate activist Joe Romm takes it very seriously:
• Joe Romm, NSIDC bombshell: Thawing permafrost feedback will turn Arctic from carbon sink to source in the 2020s, releasing 100 billion tons of carbon by 2100, Climate Progress, 17 February 2011.
If you click on just one link of mine today, let it be this! He writes in a clear, snappy way. But let me take you through some of the details in my own more pedestrian fashion.
For starters, the Arctic is melting. Here’s a graph of Arctic sea ice volume created by the Pan-Arctic Ice Ocean Modeling and Assimilation System—click to enlarge:
The blue line is the linear best fit, but you can see it’s been melting faster lately. Is this a glitch or a new trend? Time will tell.
2011 is considerably worse than 2007, the previous record-holder. Here you can clearly see the estimated total volume in thousands of cubic kilometers, and how it changes with the seasons:
As the Arctic melts, many things are changing. The fabled Northwest Passage is becoming a practical waterway, so battles are starting to heat up over who controls it. The U.S. and other nations see it as an international waterway. But Canada says they own it, and have the right to regulate and protect it:
• Jackie Northam, Arctic warming unlocking a fabled waterway, Morning Edition, National Public Radio, 15 August 2011.
But the 800-pound gorilla in the room is the melting permafrost. A lot of the Arctic is covered by permafrost, and it stores a lot of carbon, both as peat and as methane. After all, peat is rotten plant material, and rotting plants make methane. Recent work estimates that between 1400 and 1700 gigatonnes of carbon is stored in permafrost soils worldwide:
• C. Tarnocai, J. G. Canadell, E. A. G. Schuur, P. Kuhry, G. Mazhitova, and S. Zimov, Soil organic carbon pools in the northern circumpolar permafrost region, Global Biogeochemical Cycles 23 (2009), GB2023.
That’s more carbon than currently resides in all living things, and twice as much carbon as held by the atmosphere!
How much of this carbon will be released as the Arctic melts—and how fast? There’s a new paper about that:
• Kevin Schaefer, Tingjun Zhang, Lori Bruhwiler, Andrew Barrett, Amount and timing of permafrost carbon release in response to climate warming, Tellus B 63 (2011), 165–180.
It’s not free, but you can read Joe Romm’s summary. Here’s their estimate on how carbon will be released by melting permafrost:
So, they’re guessing that melting permafrost will release a gigatonne of carbon per year by the mid-2030s. Moreover, they say:
We predict that the PCF [permafrost carbon feedback] will change the Arctic from a carbon sink to a source after the mid-2020s and is strong enough to cancel 42-88% of the total global land sink. The thaw and decay of permafrost carbon is irreversible and accounting for the PCF will require larger reductions in fossil fuel emissions to reach a target atmospheric CO2 concentration.
One of the authors explains more details here:
“The amount of carbon released [by 2200] is equivalent to half the amount of carbon that has been released into the atmosphere since the dawn of the industrial age,” said NSIDC scientist Kevin Schaefer. “That is a lot of carbon.”
The carbon from permanently frozen ground known as permafrost “will make its impact, not only on the climate, but also on international strategies to reduce climate change Schaefer said. “If we want to hit a target carbon concentration, then we have to reduce fossil fuel emissions that much lower than previously calculated to account for this additional carbon from the permafrost,” Schaefer said. “Otherwise we will end up with a warmer Earth than we want.”
The carbon comes from plant material frozen in soil during the ice age of the Pleistocene: the icy soil trapped and preserved the biomass for thousands of years. Schaefer equates the mechanism to storing broccoli in the home freezer: “As long as it stays frozen, it stays stable for many years,” he said. “But you take it out of the freezer and it will thaw out and decay.”
Now, permafrost is thawing in a warming climate and “just like the broccoli” the biomass will thaw and decay, releasing carbon into the atmosphere like any other decomposing plant material, Schaefer said. To predict how much carbon will enter the atmosphere and when, Schaefer and coauthors modeled the thaw and decay of organic matter currently frozen in permafrost under potential future warming conditions as predicted by the Intergovernmental Panel on Climate Change.
They found that between 29-59 percent of the permafrost will disappear by 2200. That permafrost took tens of thousands of years to form, but will melt in less than 200, Schaefer said.
Sound alarmist? In fact, there are three unrealistically conservative assumptions built into this paper:
1) The authors assume the ‘moderate warming’ scenario called A1B, which has atmospheric concentrations of CO2 reaching 520 ppm by 2050 and stabilizing at 700 ppm in 2100. But so far we seem to be living out the A1F1 scenario, which reaches 1000 ppm by century’s end.
2) Their estimate of future temperatures neglects the effect of greenhouse gases released by melting permafrost.
3) They assume all carbon emitted by permafrost will be in the form of CO2, not methane.
Point 2) means that the whole question of a feedback loop is not explored in this paper. I understand why. To do that, you can’t use someone else’s climate model: you need to build your own! But it’s something we need to study. Do you know anyone who is? Joe Romm says:
Countless studies make clear that global warming will release vast quantities of greenhouse gases into the atmosphere this decade. Yet, no climate model currently incorporates the amplifying feedback from methane released by a defrosting tundra.
If we try to understand this feedback, point 3) becomes important. After all, while methane goes away faster than CO2, its greenhouse effect is much stronger while it lasts. For the first 20 years, methane has about 72 times the global warming potential of carbon dioxide. Over the first 100 years, it’s about 25 times as powerful.
Let’s think about that a minute. In 2008, we burnt about 8 gigatonnes of carbon. If Schaefer et al are right, we can expect 1 extra gigatonne of carbon to be released from Arctic permafrost by around 2035. If that’s almost all in the form of carbon dioxide, it makes our situation slightly worse. But if a lot of it is methane, which is—let’s roughly say—72 times as bad—then our situation will be dramatically worse.
But I don’t know how much of the carbon released will be in the form of methane. I also don’t know how much of the methane will turn into other organic compounds before it gets into the atmosphere. I’d really like to know!
I hope you learn more about this stuff and help me out. Here are a few good references available for free online, to get started:
• Edward A. G. Schuur et al, Vulnerability of permafrost carbon to climate change: implications for the global carbon cycle, Bioscience 58 (2008), 701-714.
• David M. Lawrence, Andrew G. Slater, Robert A. Tomas, Marika M. Holland and Clara Deser, Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss, Geophysical Research Letters 35 (2008), L11506.
• Amanda Leigh Mascarelli, A sleeping giant?, Nature Reports Climate Change, 5 March 2009.
The last one discusses the rise in atmospheric methane that was observed in 2007:
It also discusses the dangers of methane being released from ice-methane crystals called methane clathrates at the bottom of the ocean—something I’m deliberately not talking about here, because it deserves its own big discussion. However, there are also clathrates in the permafrost. Here’s a picture by W. F. Kuhs, showing what methane clathrate looks like at the atomic scale:
The green guy in the middle is methane, trapped in a cage of water molecules. Click for more details.
If you know more good references, please tell me about them here or add them to:
• Permafrost, Azimuth Library.