“Permafrost carbon emissions are likely to be felt over decades to centuries as northern regions warm, making climate change happen faster than we would expect based on projected emissions from human activities alone.” — Climate Change and the Permafrost Carbon Feedback
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(Extent of Northern Hemisphere 1 meter soil organic carbon store in the now thawing and burning permafrost. At about 1,000 billion tons, it’s more than enough to put a hefty strain on the IPCC’s remaining 275 billion ton carbon budget. Image source: Stockholm University.)
For a moment, let’s consider some rather difficult to deal with numbers —
790 billion tons — that’s the so-called ‘carbon budget’ the Intergovermental Panel on Climate Change (IPCC) estimates we need to stay within to prevent 2 degrees Celsius (3.6 degrees Fahrenheit) of warming in just this Century (note that current stated fossil fuel reserves hold enough carbon to exceed this budget many times over). It’s the level IPCC says we need to stay below to prevent ‘bad outcomes.’ A rate of warming that does not including later temperature increases in following centuries — which would be about double the 21st Century’s amount if global greenhouse gas levels managed to plateau and the global carbon stores remained on good behavior.
515 billion tons — that’s the amount of carbon humans have already emitted into the atmosphere. It leaves us with less than 275 billion tons remaining.
About 24 years — that’s how long it will take for humans to burn enough fossil fuels and emit enough carbon (at current and projected rates) to use up that ‘carbon budget.’ A break-neck pace of burning and dumping of carbon that is now probably about six times faster than at any time in the geological record. Faster than the atmospheric carbon accumulation during the last hothouse extinction — the PETM. Faster than during the worst hothouse mass extinction of all — the Permian.
Hitting Carbon Limits
Sound like we’re up against some hard limits? Well, we are. Because the above basically implies that human emissions would need to start falling dramatically now and get to near zero by 2050 to meet IPCC’s goal. A limit that, by itself, may have built in too much slack and may not have taken into account other responses from the Earth climate system.
Now let’s consider these new numbers from a recent permafrost study released earlier this month in the context of IPCC’s ‘carbon budget…’
0.6 degrees Celsius — that’s the pace at which the Arctic is warming each and every decade. According to the new study:
This is causing normally frozen ground to thaw — exposing substantial quantities of organic carbon to decomposition by soil microbes. This permafrost carbon is the remnant of plants and animals accumulated in perennially frozen soil over thousands of years, and the permafrost region contains twice as much carbon as there is currently in the atmosphere.
This amounts to about 1400 billion tons and around 1,000 billion tons in the shallow carbon store alone. A massive fireplug of carbon stored in thawing (and burning) land-based permafrost in the Northern Hemisphere at a shallow depth of zero to 3 meters. The new study expects 40 to 170 billion tons of this carbon store to release over the next 85 years. A further 120 to 300 billion tons could hit the atmosphere by 2300 if the ongoing thaw in the north continues.
(Model estimates of potential carbon release from permafrost. Note that Pg carbon is roughly equivalent to gigatons of carbon. Image source: Climate Change and the Permafrost Carbon Feedback.)
So where does that leave our so-called carbon budget?
Averaging the report’s findings, we can add about 92 gigatons of baked-in feedback from the shallow permafrost zone alone and end up with 607 billion tons of carbon (human + expected permafrost). This leaves us with about 15 years before we are locked in to hit the ‘2 C limit’ of around 450 ppm CO2 by end Century (not considering a current 485 ppm CO2e level or end Century CO2e of 530 to 550 ppm when all other greenhouse gasses are added in).
In addition, the 120 to 300 billion additional tons from the shallow permafrost store expected to keep out-gassing through 2300 would ultimately result in a carbon pool that pushes atmospheric values up to 480-530 ppm CO2 (560 to 600 CO2e) and turns the ‘2 C limit’ into a 4-6 C (7.2 to 10.8 F) long term climate bake.
Carbon Debt With Compound Interest
Looking at the report’s numbers leaves us with the all-too-salient impression that we really don’t have a carbon budget at all. What we have is carbon bankruptcy. A carbon compounded debt shock enough to crack the whole of the Earth System carbon piggy bank and bleed out gigaton-sized carbon pennies for decades and centuries to come. And the new shallow permafrost carbon feedback estimate does not include the approximate 400 gigatons of carbon in the deep permafrost. Nor does it consider ocean carbon stores — which may provide their own carbon debt spiral. Nor does it include Antarctic carbon stores or a number of other possible stores that could be pushed out by heat stress.
Needless to say, some considered the news in the recent Nature Report ‘good.’ At least it didn’t identify a 50 gigaton methane release over one decade from the East Siberian Arctic Shelf as some other recent articles have considered. Some news reports even went so far as to call an approximate 92 gigaton release by 2100 (or a little more than 1 gigaton per year) from permafrost carbon ‘slow.’ The last hothouse extinction, the PETM, also saw similar ‘slow’ rates of release from the global carbon system. So, slow when compared to the raging 10 gigaton per year pace of current human emissions, but fast when compared to about practically anything else in geological history.
What the new report really means is that humans can’t afford to emit any more carbon. And what we need to be looking at now is a way to swiftly transition to a net carbon negative civilization — fast.
“This is not a minor feedback,” Kevin Schaefer, a prominent scientist from the National Snow and Ice Data Center said in a recent report on the new study’s findings. “… If you don’t account for it, you’ll overshoot this 2 degree target.”