Take a close look at this global temperature chart, starting in 1880. There was a considerable amount of heavy volcanic activity during the first two decades of the 20th century, associated with cooling effects. From the early 1920s we can see the start of a warming trend that added about 0.1C to the global average over the following decade. The next decade, from the early ’30s to the early ’40s there was a more stunning gain of at least 0.2C, very much equal to the gains of recent decades, but then it stopped and reversed. The reversal is often attributed to the rapid increase in sulfur gas emissions from a rapid rise in dirty coal and petroleum burning in the postwar years. These emissions led to the creation of sulfate aerosols that had a cooling influence presumably greater than the warming effect of the CO2 gases emitted by this same amount of burning. According to theories which I think are acceptable, this imbalance was changed by the institution of cleanup programs in the 1970s, which continue to this day and have been a major source of net warming. Anyway, our focus for now will just be on what happened in the warming period during the early years of the last century.
The next chart shows us the critical difference in what was going on with global land and ocean temperatures during this period, something I had not previously taken not of. Land temperatures began rising at a rapid pace after the late 19’teens, and continued doing so without interruption until the early ’40s. for a total increase of 0.4C. Ocean surface air temperatures lagged well behind, just like they are doing today, but only for awhile. Around 1935 you can see how this changed, as oceans abruptly turned the corner. Their temperatures began to outpace the rapid gains being made over land! This is what must have been the direct cause of the unusually rapid burst in overall air temperatures that we see in the first chart.
Should we be concerned? Yes, of course. We don’t know exactly what caused the oceans to switch gears at that time, but they did. Lagging behind is perfectly normal, because of the oceans’ habit of swallowing and storing a large part of increases in energy being captured instead of sending it right back into the atmosphere the way land (or sea ice) surfaces do. Meanwhile the oceans are building up internal heat reserves, which must have some kind of limit. Do we know much about the identity of that limit? This activity is useful to us today, but how dependable is it? Why did it change so abruptlyin the ’30s? If the same thing happened over the next decade we would see land temperatures rising another 0.2C, to a total of 1.9C, and oceans starting to close the gap with a potential rise from 0.8C to perhaps as much as 1.2 or 1.3C. This whole picture all came to an abrupt end in the mid-’40s, thanks to the onset of high sulfur emissions. Today we are not only in a rush to clean up more of those emissions but are hoping to stop them completely, by putting an end to all burning of coal and oil.
Today the same kind of divergence between land and ocean temperature increases is going on without interruption, but there is one big exception that needs to be accounted for—the part of the Atlantic Ocean that exists in the Northern Hemisphere. It has been warming up like crazy lately, at a rate much greater than that of any other large body of ocean water. The following map, which only has visual information and no hard data, suggests that possibly 90% of this water body has warmed at a total of around one degree, and often much more than that, over the 3 1/2 decades since the middle of the baseline period average. Those numbers alone add up to about 0.4C per decade, which is extraordinarily rapid by any standard. It may very well have been greater yet over just the last decade of the anomaly period, possibly even as great or greater than the rate of gain for all land surfaces in the NH during this same decade—for a reminder of the change in the late 1930s. Something had to have changed in the North Atlantic that has not been true of any other large ocean body, especially those that are so dominant in the SH. What caused this particular change? Will it be repeated in other oceans?
Carl