Andrew Weaver, the faculty author on Nature Geosciences' new paper on the Arctic permafrost carbon feedback (not to be confused with the new paper implying the risk of a catastrophic Antarctic carbon feedback), is talking about the paper from his perch at the Huffington Post. He offers his take on the committed warming in the pipeline:
The last time the Earth was two degrees warming was the mid-Pliocene. That was about three million years ago. So common sense would suggest we prepare for a world that looks similar to the mid-Pliocene. Well . . .
* Sea levels were between 15m and 25m higher.
* The WAIS repeatedly melted back (repeatedly), potentially uncovering large carbon reserves.
* The Arctic was 10C-20C hotter than the present day (suggesting that while our climate models can't fully reproduce the degree of Arctic amplification we observe today, it's likely to be a real and persistent feature of the climate system.)
It will be interesting to see how cost/benefit estimates change once this permafrost carbon feedback is "priced in" to economic models of climate change. On the one hand, damages will increase. On the other hand, the differences between BAU and intensive mitigation scenarios will decrease, because the permafrost feedback will cause less warming in a hotter world, and more warming in a cooler world. Just to give a simple illustration, consider a carbon feedback that adds 100ppm of CO2 to the atmosphere. Then overlay that atop two scenarios:
* Aggressive mitigation -- 450ppm CO2
* BAU -- 800ppm CO2
Those numbers go into this equation:
Where C(0) is preindustrial CO2 (280ppm), and C is 450ppm and 800ppm, respectively. Do that and we get a forcing of 2.5W/m^2 vs 5.6W/m^2. But look what happens when we add the permafrost carbon:
* Aggressive mitigation -- (450 + 100=) 550ppm CO2 = 3.6W/m^2
* BAU -- (800 + 100=) 900ppm CO2 = 6.2W/m^2
Both forcings have increased, but the mitigation scenario has increased far more, making the difference between mitigation and carbocide somewhat smaller: 2.6W/m^2 compared to 3.1W/m^2.
It's not a huge difference, but it narrows the difference between action and inaction, and least in terms of forcing. At the same time all scenarios get more expensive and destructive. It'll be interesting to see which effect is stronger.
Instrumental records have clearly revealed that the world is about 0.8°C warmer than it was during pre-industrial times. Numerous studies have also indicated that as a consequence of existing levels of greenhouse gases, we have a commitment to an additional future global warming of between 0.6 and 0.7°C. Our analysis points out that the permafrost carbon feedback adds to this another 0.4 to 0.8°C warming. Taken together, the planet is committed to between 1.8 and 2.3°C of future global warming -- even if emissions reductions programs start to get implemented.So <+2C is off the table, unless we geoengineer (Planet 3.0 is revisiting the subject now). So there's that.
The last time the Earth was two degrees warming was the mid-Pliocene. That was about three million years ago. So common sense would suggest we prepare for a world that looks similar to the mid-Pliocene. Well . . .
* Sea levels were between 15m and 25m higher.
* The WAIS repeatedly melted back (repeatedly), potentially uncovering large carbon reserves.
* The Arctic was 10C-20C hotter than the present day (suggesting that while our climate models can't fully reproduce the degree of Arctic amplification we observe today, it's likely to be a real and persistent feature of the climate system.)
It will be interesting to see how cost/benefit estimates change once this permafrost carbon feedback is "priced in" to economic models of climate change. On the one hand, damages will increase. On the other hand, the differences between BAU and intensive mitigation scenarios will decrease, because the permafrost feedback will cause less warming in a hotter world, and more warming in a cooler world. Just to give a simple illustration, consider a carbon feedback that adds 100ppm of CO2 to the atmosphere. Then overlay that atop two scenarios:
* Aggressive mitigation -- 450ppm CO2
* BAU -- 800ppm CO2
Those numbers go into this equation:
Where C(0) is preindustrial CO2 (280ppm), and C is 450ppm and 800ppm, respectively. Do that and we get a forcing of 2.5W/m^2 vs 5.6W/m^2. But look what happens when we add the permafrost carbon:
* Aggressive mitigation -- (450 + 100=) 550ppm CO2 = 3.6W/m^2
* BAU -- (800 + 100=) 900ppm CO2 = 6.2W/m^2
Both forcings have increased, but the mitigation scenario has increased far more, making the difference between mitigation and carbocide somewhat smaller: 2.6W/m^2 compared to 3.1W/m^2.
It's not a huge difference, but it narrows the difference between action and inaction, and least in terms of forcing. At the same time all scenarios get more expensive and destructive. It'll be interesting to see which effect is stronger.
Dr. Lumpus Spookytooth, phd.
ReplyDeleteawwwww. no comments again.
"The last time the Earth was two degrees warming was the mid-Pliocene. That was about three million years ago."
you fail to mention earth is below average temperature and below average levels of atmospheric co2.
The Ordovician and the Carboniferous period were the only times when temperatures were as low as they are today.
Signed, sealed and owned Mr. Tracker.
"you fail to mention earth is below average temperature and below average levels of atmospheric co2."
ReplyDeletePerhaps because I'm not a scientifically illiterate moron who would think such a statement has meaning.
"Signed, sealed and owned Mr. Tracker."
Teh stupid, it burns.