Take a good look at the next two charts, and save them somewhere. These are the new landmarks of climate history. As explained in yesterday’s letter, the old ones are now obsolete, based on reconstruction of evidence made by a research team that has earned high praise for the quality of its work. Global averages for temperature highs have been contained for 6000 years by the top of an almost perfectly flat tracking line, ending with a hockey stick blade that did not actually break out of the top of the tracking line until the late 1930s—probably with an assist (still talking hockey) from an El Nino event of considerable strength and duration. At the beginning of the twentieth century there was heavy volcanic activity that had caused a number of years of abnormal cooling soon after 1900. The exact starting point for the modern trend of global warming will always be debatable. The latest possible date that I can see would put the late 1920s as the base period from which the final breakout emerged. That would suggest positioning the bottom of the blade of the hockey sticky on a spot with a reading of +0.1C on the scale of the lower chart, and the top at either 1.1 or 1.2 depending on how the next few months shape up.
What about all the greenhouse gases that were emitted between 1750 and the 1920s? Why no impact, or if they had an impact what happened to it? I think most of it was cancelled out by effects stemming from the emissions of one other gas, sulfur dioxide (SO2). We can’t forget that a large share of the CO2 emissions during this period were derived from the burning of dirty coal, which is loaded with sulfur. The sulfur ends up in the formation of sulfate aerosols that interact with clouds and cause cloud tops to brighten and reflect more than the usual amount of sunlight. Would this cooling effect be great enough to cancel all of the warming effect due to the greenhouse energy production of both CO2 and methane? Methane emissions, remember, are not associated with sulfur output or anything like it, and methane’s rapid growth during this period was great enough to rival CO2 in warming impact. Overcoming this combination would place SO2 on a kind of pedestal, of truly awesome proportions. Science has never had a good answer for proper estimation of its strength, but what else could cause so much cooling, and do so in a proportionate way that followed along the very same trendline as the growth of warming emissions for 170 years? I don’t think we can ignore the things that James Hansen keeps trying to convince us of, about the remarkable total power of this material.
The likely fact that temperatures did not climb for those 170 years means there was no reason for ocean waters to warm up and thus no reason to expect any increase in the water vapor content of the atmosphere. That situation began to change in the ’30s, slowed down for awhile, then began to advance rapidly as a feedback to the warming trend that started in the late ’70s. For almost two centuries, growth possibilities for the strongest of all greenhouse gases had been completely absent, but not so for CO2 and methane. They kept building up their presence in the atmosphere, constantly generating real greenhouse effects. These effects happened to be just strong enough to prevent the large amount of actual cooling that would have occurred, because of the sulfur emissions, if all of the greenhouse emissions had failed to build higher concentrations and thus remained ineffective similar to the even more pronounced absence of water vapor. Today, if you believe Hansen’s theories are correct, we are seeing major reductions in the cooling effect of SO2 that once held back the warming impact of CO2, methane, several other GHGs, along with their normal water vapor feedback. The latter was always compelled to await the actual warming of surface waters for evaporation to make a move.
The transformation is not yet complete. There is about as much coal being burned today as there ever was, and a peak in oil burning adds its own share of sulfur emissions, but the total cooling effect of coal and oil burning has probably been reduced to an amount less than half of what it would be today if it had remained untouched. Let’s just arbitrarily pick a number and say that 33% of the sulfur cleanup potential remains unfinished. (It will only be completely finished when all burning of these fuels has ceased.) By implication, that means the amount of temperature increase we have witnessed since the 1930s is only about two-thirds complete from the standpoint of taking into account all of the effects of all the gaseous emissions due to the burning of fossil fuels. If we stop all of the burning temperatures should quickly move up to 100% of their pure, unchecked greenhouse potential. These should be at least 50% greater than the increases we’ve already gotten, and which are probably not yet complete in terms of achieving full equilibrium. Any additional growth in GHG emissions after today, plus an assortment of expected feedbacks, would create new gains to be tacked on, and who knows how many other kinds of tipping points are out there ready to be broken into at this advanced level?
Carl