Before continuing to expand upon the water vapor issues, I need to add a bit more to the interpretation of the odd-looking chart posted at the top of yesterday’s letter. Best that I post it again today:
You may have wondered, as I did for awhile, why that big dip in temperature forcing that we see around 1990 does not have any kind of direct impact on an actual temperature map, like the one shown here:
It’s simply because the numbers on the top chart (in both w/sqm and temp) only represent the running greenhouse gas contribution within a much bigger and sphere of influence. The big picture, if it could be accurately charted, would include the same kind of numbers, positive and negative, for everything that has an actual effect of surface temperatures. Some of these can exhibit even stronger trends or greater fluctuations. Hansen’s reference to the major trend in sulfate aerosol reduction is just one of them. Other examples include effects of El Nino cycles, volcanic eruptions, sea ice melting, temporary shifts in regional climates and so on. They all contribute to the final result each year, some as a blending of cyclical fluctuations and some as parts of a major trend. As Hansen sees things, the sulfur cleanup activity could very well have been the cause of the dominating major trend ever since 1970. We sure don’t see anything comparable in the overall trend of greenhouse gas forcings, given the declines in CFCs and methane.
Now we can talk about water vapor again. Water vapor is known to be the strongest of all greenhouse gases in terms of standard energy-trapping power within the radiation bands. It is by far the most abundant gas, yet also the most irregular in distribution, to an extreme. It is known to have a significant effect on global temperatures, but scientists who have looked into this question were not sure of exactly how much until a team led by Andrew Dessler came up with a reasonable answer in 2008. Here is a review of their study: https://www.eurekalert.org/news-releases/551246. I believe this work is accepted throughout the industry as the best possible appraisal of what water vapor contributes to global temperatures. That’s just the starting point for my story.
Just today, doing a bit of quick research, I stumbled upon an interview given by Dessler to EarthSky magazine back in 2010, which I urge you to read. It contains a number of nuggets of information that greatly help to reveal the origins of a point I keep trying to make, about how science goes wrong in its interpretation of the water vapor feedback. There is such a pervasive feedback effect behind any water vapor changes, which best explains how the power of water vapor expands within the system, and there is little to doubt about the size of the power that is exercised, but here is the sticking point: “To What?” is it a feedback? .Conventional science keeps telling us it is a feedback to CO2, the strongest of all the well-mixed greenhouse gases. I have said many times in these letters that this is an erroneous interpretation, leading to many kinds of errors and distortions, and should be rooted out. The reality (in my mind) is that water vapor is a feedback to changes in surface temperatures, no matter what causes those temperatures to change, including and beyond the effects of CO2 and all the other greenhouse gases. Now I’m going to quote what Dessler himself has to say in regard to this subject, as expressed within the EarthSky interview:
1. “Dessler explained that water vapor has been proven to be a major contributor to global warming. He said carbon dioxide emissions provide the initial warming, by increasing surface temperatures on the planet. Warmer temperatures cause more water to be evaporated off the oceans, which increases the amount of water vapor, or humidity, in the air.” [Each sentence is right, except that, in fact, CO2 emissions are generally a major provider of the initial warming, rather than the single provider that is implied by his wording.]
2. “The higher humidity in the atmosphere, because water vapor is a greenhouse gas, gives you additional warming. It’s that amplification that we call the ‘water vapor feedback.’ ” [The first sentence is correct. The second is kind of confusing, not the best definition of “water vapor feedback” if it is actually caused by increases in surface water temperature.]
3. “You get twice the warming with the water vapor feedback than you would without the water vapor feedback.” [Probably true, and a most remarkable finding from the study made by Dessler’s team.]
4. “In other words, water vapor makes carbon dioxide twice as effective at warming the planet.” [Quite true, but the exact same thing can (and must) be said for all the other things, of every kind, that help to warm the planet.]
5. “He said that almost all of the water vapor in the atmosphere comes from evaporation off oceans, not from human activities. Dessler added that water vapor doesn’t act like most other greenhouse gases.” [Both are good points.]
6. “The important thing to realize with water vapor – it is the biggest greenhouse gas – but it’s tied tightly with surface temperature. If you know what the surface temperature of the planet is, you know how much water vapor is in the atmosphere.” [Basically correct, no matter what the cause of surface temperature may be. However, I think the “tie” is probably not so “tight” for the amount of vapor content that exists at higher altitudes.]
7. “Dessler broke down the numbers for the common scientific assumption of 3 degrees Celsius of future warming…..Most of that warming turns out to come from feedback, not the direct warming of carbon dioxide. Carbon dioxide alone would give you one degree…..[my ital. This statement, all by itself, is correct as it stands, but why does he not account for the other gases when CO2 is actually never “alone” as a functional GHG?]…..and then the water vapor feedback gives you another degree, and then there are a bunch of other feedbacks give you the last degree. But of the feedbacks, water vapor is the most important one” [and would account for fully half of the last degree].
Dessler’s apparent mindset tends to allow gross exaggeration of the importance of CO2 over other GHGs, making it virtually identical to the mindset adopted by the entire climate science community, including James Hansen. It is blatantly wrong, causing an endless series of substandard forecasts in the models, which all need to be corrected.
Carl