Climate Letter #2066

COP26 is now over with. Many publications have summarized the outcome in much the same manner, and I’m sure most readers are already familiar with this basic viewpoint. In short, some real progress, outweighed by too much disappointment. The progress is just enough to keep alive the hope that global warming can still be held to an increase of no more than 1.5C above pre-industrial. In that regard, according to a well-researched new study, reviewed here in the last two letters, there was no increase at all between the pre-industrial timing dated at around 1750 and the late 1930s, which means we can use the average annual temperatures of the late ’20s and early ’30s as a reasonable starting point for the modern trend in its entirety. Doing so gives us a best current fit of +1.1C, which in fact is unchanged from previous calculations that were always fraught with minor uncertainties from a record-keeping standpoint. We also have a clear view of a straight-line increase in warming of 0.8C just since the beginning of the 1970s, which translates into a rate of +0.16C per decade. This barely allows us two full decades to get everything done that needs to be done in order to avoid passing the +1.5C target-limit—provided there is no acceleration in the linear nature of the trendline.

Doing everything that needs doing is a monumental enough challenge; the obstacles are both visible and powerful. Then what about the possibility of an acceleration in the warming trend? Could it happen even if human actions are at least partially attenuated?  This is a subject that does not get much attention.  Whatever forces are required to do the accelerating would need to be of a completely natural type, vviewed as pure products of the momentum that has already been established and continues to work behind the scenes.  Nature often does work that way, so it can’t be ruled out.  Nor can we do much of anything to stop it, but we can at least alert ourselves to the possibility, and once we are aware of any real danger we can turn our thoughts toward the best modes of preparation.  Sea level rise is often discussed with this in mind, setting a proper example even if the level of acceptance so far and need for serious planning both fall short.  Accelerated temperature increases are less commonly discussed because the things that might cause them are not quite as visible.  I have taken more interest in such things and have noted several findings that fall into this category in recent months. More than ever I can see the need for watching out for these obscure happenings, out of a sheer feeling that being alert and realistic should do more good than harm.  Today I am going to add one more item to the list.  This is something I have been dimly aware of for quite some time but have never had a good handle on how to deal with it or taken the time to follow good leads.  It concerns the melting of Arctic sea ice and what it may be leading up to.

A report was published in October of last year by the journal Nature Communications under the heading, “Global warming due to loss of large ice masses and Arctic summer sea ice.”  The work was authored by individuals connected to Germany’s Potsdam Institute, which sponsored the research.  Open access of the study is available:  https://www.nature.com/articles/s41467-020-18934-3. The main point is this: now that the CO2 level has risen above 400ppm, the melting effects from all of Earth’s large ice masses caused by the greenhouse warming are likely to raise global temperatures by an additional total of 0.43C over time.  Arctic summer sea ice is singled out as the ice mass causing the largest part of this increase, at +0.19C, and also the quickest.  New Scientist magazine wrote up a clear summary of the findings, which can be read at this link:  https://www.newscientist.com/article/2258169-arctic-sea-ice-loss-could-trigger-huge-levels-of-extra-global-warming/.  Quoting from their article, “They found that the loss of ice in all four places would, over centuries to millennia, contribute an extra 0.43°C of warming globally in the event of the world holding temperature rises to 1.5°C.  However, Arctic feedbacks could bring warming on much shorter time scales. Summers in the region are expected to be ice-free before 2050. That means the Arctic alone could account for an extra 0.19°C of global warming around mid-century, on top of the 1.5°C……The Arctic feedbacks would have an even bigger impact locally, raising temperatures 1.5°C in a region that is warming faster than the rest of the world and beset by record fires.   

This last sentence could raise the question in one’s mind about whether the Arctic really needs to wait for entire world to reach a temperature target of +1.5C before summer sea ice melting is completed, or is regional warming alone capable of getting the job done? Does the ice have any way of discriminating? I believe the average gain for Arctic region as a whole now clearly exceeds 1.5—today, for example, has a reading of +2.1C on the weather maps, not too unusual, and that only covers a period three decades old. And there seems to be some recent acceleration, for reasons that must be unrelated to contrary trends now occurring in Antarctica. I would call it an example of a self-amplifying feedback: as the Arctic Ocean loses some of its ice cover it absorbs more sunshine and responds like any one of us would while sitting in the sun. The added warmth in this case can only serve to melt more ice, right then and there.

Carl