A remarkable new study reveals a steady trend of decline in “global dimming” since 1998. The actual trend has been recorded in two different ways, by two unrelated sources, with results that are basically similar except that one shows a faster rate of decline than the other. The new study was published by the group that did the research behind the slower rate. They obtained data from the other source (CERES, run by NASA), which is otherwise not readily available, making it easy to compare the two on one chart. Here is a link to the press release from the report’s publisher, issued on Sept. 30: https://news.agu.org/press-release/earth-is-dimming-due-to-climate-change/. It includes the image of both trends, repeated here for quick reference purposes. Note how the scale is designated in watts per square meter (W/m2), which is readily convertible into temperature changes, that in this case would be upward. (The full report has open access at https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL094888)
This report, which is a real bombshell, has received a great deal of attention in the media, especially the online climate science media, and it should, because the data is so unexpected. The slow trend ends up with a total decline 0.5 W/m2 over two decades, which translates into roughly 0.375 degrees C of warming under the well-accepted 75% rule. The trend of global warming over the past 50 years has actually been moving along at a quite steady pace of 0.18C per decade, prior to an apparent bumping up of recent movement. The slower trend data, and the project behind it, came to an end in 2017 at a low point that just misses most of the actual acceleration. The CERES data, extending one more year, has certainly not missed it. This project has no end point, and leaves us wondering about results have been like for the last two years. Maybe now they will do some regular publishing on their own?
Everyone would like to know what’s going on here. How far back in time did this strange trend start to develop, and what could cause so much strength. Assuming there is no mistake, everything points to the realization of an extraordinary increase in solar energy reaching the surface of the planet, almost certainly based on a high amount of reduction in overall planetary albedo effects. So much warming from this one source leaves little room any amount of increase in the reception of energy delivered by greenhouse gas producers. We are not exactly accustomed to hearing that kind of talk, so lots of questions are in order. The obvious one to start with would be, where could all this albedo decline be coming from? The authors of the report, followed by nearly every commentary I have read, place the responsibility almost entirely on changes in cloudtop albedo, which makes sense, but only if one can explain which clouds and why so much change. This will be an ongoing challenge.
The first thing that came to my mind when I saw this story was the James Hansen scenario, which I have been thinking and writing about for a good part of the last full week. Please go back and read his July Temperature Update again, (at http://www.columbia.edu/~mhs119/Temperature/Emails/July2021.pdf) where he says, “None of the measured forcings can account for the global warming acceleration…..It follows that the global warming acceleration is due to the one huge climate forcing that we have chosen not to measure: the forcing caused by imposed changes of atmospheric aerosols.” According to Hansen, the sulfate aerosols that at one time were making the air so dirty were also causing cloudtops to brighten. The massive air cleanup program that began in the 1970s has been tasked with reducing those aerosols as rapidly as possible. The program has enjoyed a record of considerable success, which must have had the result of making the cloudtops less bright while the air was being cleaned. This work is not finished, and as Hansen points out, has lately accelerated. Interesting.
For Hansen’s scenario to be true, the original cooling effect must have been of the same total magnitude as that of the still incomplete warming effect that is now causing its undoing. The accumulated cooling will need to be exhibited as an integral part of climate history, from a time before the creation of sulfate aerosols from burning of coal and oil, or whatever else, ever entered the picture. Another challenge for the model-makers.
Carl