Friday’s letter provided evidence that current temperature changes in Antarctica at this time of year are almost totally dependent on changes in the precipitable water content of the air directly above the surface. The data displays also show the enormous power of leverage that is involved when the actual content of this greenhouse gas is capable of being doubled over and over again within a relatively brief period of time and shortness of distance. Temperatures can change by 10-20C in a matter of hours and then by another 10-20C within one hundred miles or so, followed by a trail of similar changes extending for many more hundreds of miles. That’s what happens when you start with a content value close to zero and then have the flexibility to raise that value by as much as fifty times or more in one big long swish. Precipitable water streams coursing at high altitude are the one form of greenhouse gas that has that capability, and mid-winter Antarctica is the perfect place to show it off.
Water vapor is different from all other greenhouse gases mainly because of the extremely short lifetime of each molecule following its birth by evaporation, and also because its birth is so dependent on how warm that water may be. When the birth rate is high the molecules quickly start looking for less crowded conditions, the same thing all other gases are prone to do, but those made of water only have a few hours or days to get somewhere before condensing and falling back to the surface. Other gases have more time to expand and can thus spread out across the entire atmosphere, which becomes their durable legacy. As such no place remains where a doubling is ordinarily possible except over a time period of probably hundreds or thousands of years. Carbon dioxide, all by itself, has added about six tenths of one degree to the everyday temperature of Antarctica, and everywhere else as well, which took 250 years to accomplish while making half a double. Methane has done about as well in this time by more than doubling. They both are adding a tiny, tiny bit to those increases over the course of each year. Down in Antarctica water vapor can add a full 10-20 degrees to a particular local temperature in just one day and then, solely by reducing the rate of infusion, cause all of that to be lost plus another 20 degrees in the very same place over just the next few days. Here is a picture of the result:
Notice how there are either warm or cold anomalies of five to ten degrees or more over practically every corner of the continent. It is like that almost every day now, with locations constantly shifting around. Every spot gets an infusion of either no vapor at all or just a small dose every day, thereby creating a running average against which each new day will be compared, sometimes one way and then the other. If you go to the animated website from the U of Wisconsin at http://tropic.ssec.wisc.edu/real-time/mtpw2/product.php you can watch it all happening in nearly real time. You will also see how utterly different the water vapor infusion rate is in the other polar region, where things have really gotten out of hand this summer. Winter will soon be back and then we can make a whole new set of comparisons between these two special regions.
What makes Antarctica so especially interesting right now is that nothing else is available to cause temperature anomalies from one day to the next. As mentioned before, all other greenhouse gases do not change. There is no sunlight at all and thus no clouds or anything else can exercise an albedo effect. There is no cold rain at all coming down, and not much snow either when it’s this cold. Surface winds have no visible effect on temperature here. The regular flux of radiation coming off this surface of pure ice is at an absolute low, never replenished or altered like all other surfaces are every day everywhere else. Water vapor is the only effective force of change that remains, so measuring its effectiveness is not too complicated. What I keep seeing is 10 degrees for each double, locally only, and only for as long as the increase may last.
There is one other matter of interest, where the Windy website https://www.windy.com/ proves to be quite helpful. Clouds are widely recognized for having their own greenhouse effect, but one that is very difficult to measure. How might it differ from the greenhouse effect of the water vapor that all clouds are composed from? In Antarctica some places are clouded over and some are not. As far as I can see it makes no difference at all on the air temperatures below, for whatever that information is worth.
Carl