Study underestimates impacts with conservative assumptions
Figure: Carbon emission (in billions of tons of carbon a year) from thawing permafrost.
The thaw and release of carbon currently frozen in permafrost will increase atmospheric CO2 concentrations and amplify surface warming to initiate a positive permafrost carbon feedback (PCF) on climate…. [Our] estimate may be low because it does not account for amplified surface warming due to the PCF itself…. We predict that the PCF 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.
That’s the stunning conclusion from “Amount and timing of permafrost carbon release in response to climate warming” (subs. req’d), a major new study in Tellus by NOAA and the National Snow and Ice Data Center (NSIDC). As we’ll see, the figure above is almost certainly too conservative post-2080.
The permafrost permamelt contains a staggering “1.5 trillion tons of frozen carbon, about twice as much carbon as contained in the atmosphere, much of which would be released as methane. Methane is 25 times as potent a heat-trapping gas as CO2 over a 100 year time horizon, but 72 times as potent over 20 years! One of the most conservative assumptions the study made, the lead author Dr. Kevin Schaefer confirmed in an email, is that all of the carbon would be released as CO2 and none as methane.
The carbon is locked in a freezer in the part of the planet warming up the fastest (see “Tundra 4: Permafrost loss linked to Arctic sea ice loss“). Countless studies make clear that global warming will release vast quantities of GHGs into the atmosphere this decade. Yet, no climate model currently incorporates the amplifying feedback from methane released by a defrosting tundra. Heck, the NSIDC/NOAA study itself doesn’t even incorporate the CO2 released by the permafrost carbon feedback into its warming model!
Even so, in their study, the permafrost is adding more than one billion tons of carbon a year to the atmosphere by the mid-2030s!
Here’s some background on the permafrost and the study from the NSIDC release, “Thawing permafrost will accelerate global warming in decades to come, says new study”:
“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% 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.
The authors note that of the dozen or so studies done to date on permafrost melt by 2100, “Our projections of permafrost degradation fall on the low side, but well within the range of other published projections.” An earlier NCAR-led study found half the land-based permafrost would vanish by mid-century on our current emissions path (see “Tundra, Part 2: The point of no return“).
The NSIDC-led study acknowledges that it almost certainly underestimates the warming the PCF will cause. As noted, it assumes all of the carbon released will come out as CO2, not methane. It doesn’t attempt to calculate and incorporate the extra warming from that CO2. And its land surface model excludes some permafrost areas. In addition:
We use surface weather from three global climate models based on the moderate warming, A1B Intergovernmental Panel on Climate Change emissions scenario….
The A1B scenario has atmospheric concentrations of CO2 around 520 ppm in 2050 and 700 in 2100. We’re currently on the A1F1 pathway, which would takes us to 1,000 ppm by century’s end, but I’m sure with an aggressive program of energy R&D we could keep that to, say 900 ppm.
More to the point, the A1B is stabilization scenario, with concentrations constant at 700 ppm after 2100. As the study notes:
The start of permafrost thaw typically occurred 25 or more years after warming started and 20% of the total thawing occurred after warming stopped in 2100. The models driven by the A1B scenario, none of which included the PCF, all stabilize at a new, warmer climate after 2100 when CO2 concentrations level out at 700 ppm. However, our simulations indicate that the global carbon cycle will not stabilize until at least 2200. Nearly all thawing of permafrost carbon occurred before 2100, but 46% of permafrost carbon flux occurred after 2100. Once thawed, the permafrost carbon can take 70 years or more to decay due to cold soil temperatures and periodic refreezing. This slow response means that once the PCF starts, it will continue for a long time.
So in the real world, where the PCF actually contributes to warming along with myriad other carbon cycle feedbacks, the defrosting will likely continue to increase past 2100. Even with all these conservative assumptions, the basic conclusion is sobering:
Also like fossil fuels, the PCF is irreversible: once the permafrost carbon thaws and decays, no process on human time scales can put the carbon back into the permafrost. If any international strategy to reduce fossil fuel emissions does not account for the PCF, we will overshoot our desired atmospheric CO2 concentration and end up with a warmer climate than intended.
One last point. This study only looked at the land-based permafrost. Let’s remember the study from last year:
Science: Vast East Siberian Arctic Shelf methane stores destabilizing and venting: NSF issues world a wake-up call: “Release of even a fraction of the methane stored in the shelf could trigger abrupt climate warming.” Methane and carbon release from the Arctic is the most dangerous amplifying feedback in the entire carbon cycle. This research finds a key “lid” on “the large sub-sea permafrost carbon reservoir” near Eastern Siberia “is clearly perforated, and sedimentary CH4 [methane] is escaping to the atmosphere.”
Again, the people out there who think R&D or an energy quest is going to stop us from multiple catastrophes are deluding themselves and others. We need to start aggressive mitigation now as every major independent study concludes.
Think they'll believe us now, Tenney?
ReplyDeletenah
ReplyDeletewould someone explain to me exactly how we are not doomed?
ReplyDelete