Climate Letter #1105

An update on the permafrost problem–
Thanks to Brian Resnick at Vox for putting together all this information, much of it new, with countless links to sources of high credibility.  We learn that practically all permafrost soils are getting warmer and thus getting closer to the time when they will melt, which of course has already begun in some places.  He also gives us an extensive survey of all the different kinds of things we should be expecting as a consequence, which now includes the extensive release of mercury.  Please take your time studying his report, and maybe open a few links as well.

–One link in particular should not be missed, picking up a special report from the NY Times that was created last August.  It has features, photos and background information that nicely round out the story.
–Another link refers to a 2014 study published in the journal Environmental Research Letters which provides  reasonable and fairly conservative estimate of how much carbon will be added to the atmosphere by the year 2100 as a result of permafrost thawing.  Their central estimate, admittedly rough, is 120 billion tons, which is equal to twelve years worth of all the carbon human activity is now emitting.  That by itself would add another 25 ppm of CO2 to the Keeling curve, on top of whatever humans add in a direct way, which is supposed to stop before hitting 450 ppm—which now seems a bit optimistic.  Altogether then we are looking at an atmosphere with 475 ppm by 2100, with more gases to be released by permafrost in the century following.  That is a good benchmark figure to keep in mind when other studies come up, like those dealing with climate sensitivity or with comparisons that take us back to the Pliocene era (see below).
A new study provides some lessons about the late Pliocene.  We learn, first of all, that current climate science is acceptive to the idea that the CO2 level at that time was around 400 ppm, just like it is today, and that temperatures were considerably higher than they are today.  (“Three million years ago the Earth’s climate  was warm enough to permit a forested High Arctic inhabited by large mammals.”)  Also there were variations in sea level, indicating the presence of glacial ice sheets, which came and went in response to the peaks in orbital cycles, which seesaw in their impact between the northern and southern polar regions.  The formation of those glacial sheets would imply that there were “glacial maximum” times when CO2 would fall well below 400 and temperatures get a few degrees cooler.
–There is a link at the end to a 2015 study that has interesting things to say about temperatures, CO2 levels and climate sensitivity in the late Pliocene era, consistent with the latest IPCC estimates, as described in this story:
–That study itself has a paywall, but if you open it and click the Figures button you can see charts that reconstruct the CO2 level between 2.3 and 3.3 million years ago, along with some others.  There are at least five or six different kinds of sources behind these estimates, which are then coordinated into a tighter series.  That would be the one with high points near 450 and lows near 250 plus a wavy median line that hangs around the middle.   Maybe we will need to start looking back farther yet for climate comparisons, to the early Pliocene or even the Miocene??
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