What the weather maps are saying about global temperatures at this time. We may be in the middle of a record breaking year for warmth but it does not look at all like that right now. This next image offers considerable information in support of this view. It represents anomalies from a 1979-2000 base that on average are three decades old. Over that period all of the principal global warming charts show average temperatures on a steadily rising trend of close to 0.18C per decade, for a total of 0.54C since 1990. Now look at the numbers at the bottom of the map, where the current reading of 0.2C is well below that total and also down from recent highs of around 0.9C. The entire Southern Hemisphere is actually cooler now than it was in an average year thirty years ago.
In fact over most of 2020 the Northern Hemisphere and the Arctic have been running much higher than today while the Southern has been consistently low except for when Antarctica makes an erratic bounce upward. In general the SH is being held back because it has so much of the world’s ocean water, which in turn is known to be held back for reasons mostly related to the way ice melt works. In contrast, ocean surface temperatures in the NH are currently reading 0.8C above average (over a slightly longer 1971-2000 base period). Since continental temperatures normally rise faster than ocean surfaces there are questions about why the land area of the NH is so relatively cool right now.. It’s a complicated subject, but I can suggest a few possible reasons. This next image will be helpful because it shows so much rain:
The current warm ocean waters of the NH are mostly concentrated in the western Pacific Ocean and the Indian Ocean, mainly thanks to a combination of ordinary summer heating plus a trend of strong La Nina-type wind development that is underway. The result is an extraordinary amount of evaporation and rainfall in that part of the world. Most of the evaporation may rain out over the oceans but a large fraction will always move out over land as well, which in this case mostly relates to a large part of continental Asia. I have been writing a great deal lately about high-altitude streams of water vapor, which rise to heights well above three miles under clear-sky conditions and may continue in that same mode while traveling long distances in a poleward direction. A classic example is described in CL #1721 on July 14th, where the absence of clouds over a large playing field is a remarkable feature, leading to maximized temperature anomalies due to greenhouse warming effects on the surfaces below.
What we are seeing in the present situation is quite different. The major cool anomaly in the center of the top image was also caused by a massive stream of water vapor but I think this stream is positioned down closer to the surface where it is widely distributed by surface winds. In this position the vapor can become regularly involved in cloud formation and rainfall episodes as it travels. The greenhouse warming of the vapor plus water drops and droplets may still be there, but its effect will be more than offset by the cooling induced by both the cloud albedo and the cooling of rain itself when it falls. On the above two maps you can still see that warm anomalies exist, but they are largely confined to regions where the skies have remained clear. This last map will show that the total amount of precipitable water spread out over the hemisphere is large in amount and broadly distributed. The map cannot tell us how the water content breaks down by altitude but we can still do our best to understand how much difference there is in behavior and weather effects from the two different types of streams. For the time being its cooling mode appears to have quite an advantage.
Carl