James Hansen has issued his November temperature update. These usually have something interesting to say besides ordinary data, and this one goes to an extreme in that regard. Hansen has always been controversial in one way or another. He has always been critical of government policy decisions for not following the science. Lately he has become more and more critical of the messaging being delivered to the general public, as well as to policy-makers, by the science establishment itself. Most notably, he contests the constant repetition of the idea that the average increase in global temperatures can be held to +1.5C if all the right things are done—which he thinks is literally impossible. He goes on to argue that the goal of +2.0C, if not impossible, poses enormous difficulties as well as high financial costs. Here is a link to the update, which everyone should find worthy of spending some time, and I will follow with a few selected points for commentary: http://www.columbia.edu/~jeh1/mailings/2021/NovemberTUpdate+BigClimateShort.23December2021.pdf.
Hansen repeats the claim he made in the July update, that anomalous warming in recent years is largely a consequence of efforts to clean up sulfur emissions when coal and oil are burned. These emissions create aerosols that interact with clouds in a way that causes a strong cooling effect. This cleanup program is far from complete and will continue to have a warming effect even if there are no future emissions of greenhouse gases. That’s because a significant portion of GHGs that are already present in the atmosphere, and will remain so for centuries, are currently being neutralized by this cooling effect. As the sulfur is diminished the impact of these gases will be realized instead of simply offset as they are now.
The future scenario of emissions reduction required to hold global warming to within the +2.0C target requires annual decreases to be made at a rate defined by the so-called RCP2.6 scenario, for each of the next twenty years. The following chart shows how difficult that would be without the assistance of an effective method of removing CO2 that is already in the atmosphere. Hansen has much to say about how costly that process would be, even if improvements are realized in the current technology.
Here is how Hansen puts it: “Of course, one can devise a scenario that stays under 2°C via a miraculous transition to zero emissions within a few decades, but the real world pays no attention to imaginary scenarios. Instead, the real world responds to the actual growth of greenhouse gas climate forcings, shown by the top edge of the red area…..Global warming of at least 2°C is now baked into Earth’s future. That level of warmth will occur by midcentury.” (My ital.)
One more image from the update needs to be shown, with a comment. During the last five years we have had a strong El Nino event followed by a La Nina trend that is now close to having a traditionally maximum cooling impact. The chart shows that global air temperatures are out of phase with the ENSO cycle, by an amount that appears to be around 0.1C. In other words, there was “too much” warming, by 0.1C, during the El Nino and “too little” cooling by the same amount during the La Nina, creating an unusual gap has been steady for five full years. Does it represent a permanent acceleration of the previous trend of warming, or will it tighten up at some point? Or will it widen even further, perhaps when the next El Nino arrives? Hansen says the next El Nino—not necessarily a major—is virtually certain to arrive within five years or less.
Carl