Climate Letter #1798

The technical difficulties experienced this past week on the Weather Map site have taken out all records I have of the incredible North American cold anomaly as originally reported here two days ago. This is most unfortunate because it may be a long time before we again see a cold one with so large an area that is so extreme. If anyone who read the letter that day happened to print out a color copy please let me know, and maybe it could be permanently entered into the record.

Meanwhile, I have seen enough reports and data to feel reassured that the minus-20C anomaly extending over parts of six central states was a reality. It’s an event that I keep turning over in my mind, with a sense of wonder. Let’s put this in perspective. The people who measure all of Earth’s temperatures every day tell us that the year-around average totaled up for all locations is around +15C, which is about one degree higher than the pre-industrial average. Some locations will of course have a higher than 15 average and some less, and they will all have seasonal variations. Those six central states should currently be somewhere near the middle, meaning pretty close to the 15 average, by virtue of both geography and seasonality. An anomaly of -20C meant that the combined average for the coldest part was about 5C or 9F below freezing for the full day, probably not too far off from the true number.

What does this mean? Let’s look at another number, minus-18C. This represents the average year-around global temperature that scientists assure us would be the case for our planet if there were no greenhouse gases of any kind present in the atmosphere. We need to be thankful we have them, in about the right amount for life to be comfortable, and we really should be fearful of allowing their powers to expand if we want to preserve favorable living conditions.

If -18C is rock bottom without greenhouse gas, and solar energy input is unchanged, by going from -18C to +15C we get 33C as the total average value of GHG warming at this time. Assuming that all other conditions were normal, an anomaly of -20C implies that around 60% of the GHG sources that are actively responsible for warming on a normal day suddenly went missing. Can we specify which gas, or gases, that might be? I can see only one kind that is even remotely capable of showing that much local variation in one day, water vapor, and that is because of the extremely uneven way it is distributed throughout the atmosphere. Water vapor near the surface has horizontal distribution, from the equator to the poles, that is quite extreme, and familiar to all. Changes frequently occur, but not on a scale that could have accounted for this great anomaly, or most of the other large ones we see.

This leaves the door open for one more option, vertical distribution of a similarly uneven type, a subject having much less familiarity in terms of greenhouse effects.. This is where I believe the answer can be found, by anyone willing to take a hard look at the activity that takes place every day in the troposphere’s upper-level wind system—a place where both jetstream winds and concentrated streams of water vapor can be observed in a state of perpetual motion. Away from the tropical belt, which is not layered or active in this same manner, I further believe it is quite possible that water vapor contained in the upper layer, in addition to its volatile distribution pattern, is normally responsible for a higher total amount of surface air warming than vapor in the corresponding lower layer. This possibility, along with vapor’s high energy-producing strength, could account for a maximum share of the deep cooling report, occurring when normal vapor content in the high layer was in fact almost completely absent for a day or so, blocked off by the presence of well-positioned jetstream winds.

Carl