How Deep is this Result?

There are deep results in the climate sciences. By "deep result" I mean something that would take some years of study to understand or place into context. This is an intrinsically interesting branch of physical science. (Indeed, if there were no policy issue it would probably be better funded and attract a larger number of highly talented people than it does now. But let's avoid that topic for now.)

William Stein is an accomplished mathematician and a the leader of a large open source project (that scientific programmers in the audience would do well to look into, SAGE, a replacement for Maple, Mathematica, Matlab and "Magma", the last being more of a niche product that especially interests Bill.) I had the pleasure of having dinner in his company along with various other very smart people last Monday, several of us among the climate-obsessed. Bill, however, being a very focussed person, knew very little about it. Accordingly he asked a couple of remarkably insightful newbie questions. The one I remember clearly was "how deep of a result is it?"

The response we came up with first was a bunch of caveats. Of course we cannot "prove" anything in the sense a mathematician might. Once we got that across, I pondered the question.

It emerged that Bill's question could be quantified as follows. Suppose you have a non-ideological person with a bachelor's degree in a serious mathematical science. How long would it take to complete the argument?

I quickly came to the point where I asserted that, if "it" means "greenhouse gas accumulation presents us with serious consequences over the next century" it was difficult to think of any intelligent, open-minded graduate student in the climate sciences who didn't find the proposition obvious after they had attained to a master's degree level. "So, two years then?" Bill asked? I said that was excessive: these people are studying particular phenomenologies, not the "is global warming scary" question.

So I've reached an upper bound of a few months. And I think that's roughly right. I'd think a single course (full-time equivalent of a month, possibly represented by David Archer's book "Global Warming: Understanding the Forecast") should suffice. A Ph.D. level person ought to be able to read a book like that as if it were a novel, say a few evening's concentrated work. Would that be convincing? A couple of online lectures, say Alley's and Hansen's, to ice the cake, and yes, I'd say the picture could be conveyed to a scientifically educated person in a couple of weeks of serious concentration, perhaps just a few days if that person were familiar with some of the underlying physics.

Steve pointed out that the deniers could monkey-wrench any individual argument, since we are doing earth science and not mathematics. That said, their are a number of convergent arguments, and little evidence to the contrary. And of course, denying the science is insufficient to derail the policy. It is necessary for the zero-policy position to prove a low sensitivity, but not enough to question the consensus sensitivity. So a week isn't really enough to manage the minefields of debate. In fact, time constrained "debate" as construed by many people is never really a good way to examine a broad scientific context, though one could defend an individual result that way.

But "global warming is scary" isn't a scientific result in the ordinary sense.

From a strictly philosophical point of view, "scary" isn't an objective standard. Some real-world metric for "scariness" is needed, and therein we get to difficult territory. But it's hard to compare the scope of the changes we expect with the scope we are used to and be sanguine about it.

A more serious issue is that "scariness" isn't a result in that it isn't a straightforward conclusion from laws and data to a consequence. It's a "balance of evidence" argument that leads to an estimate of how big a deal this all is.

Usually the number we use is "sensitivity", i.e., the amount of warming associated with a doubling of CO2 (or equivalent radiative forcing). That number appears to be in the neighborhood of 3 C, and that in turn leads us to expect 1) detectable changes by 1990 2) noticeable changes by 2010 and under business-as-usual 3) disruptive changes by 2050 and 4) catastrophic changes by 2100. Also, failing a scheme for removing CO2, likely a more expensive prospect than not emitting it in the first place, these disruptions will be very long-lived.

So this article is my long answer to Bill's question. I also came up with a short answer, as Steve said, "the outlines of the argument" that could be understood in a few minutes and was intended to be maximally persuasive in a few minutes. That will be another article.

This article, I think, would give any fair-minded scientist enough material to at least understand the perspective of mainstream climatologists in the absence of deliberate obfuscation (*).

* - The obfuscation, alas, is there. That is a problem we have to deal with, and how we deal with it in addressing an energetic and intelligent person who is also fully occupied with their own projects and interests is another matter. It's an important one, though, and we can't rely on PR people or politicians to do it for us.