Friday, 30 April 2010

Global warming: The big questions are still unanswered

April 29, 8:58 PMEnvironmental Policy ExaminerThomas Fuller

I have noticed in the comments to this and other sites that people unfamiliar with the imbroglio surrounding global warming tend to ask the same questions, and tend to be confused by the conflicting answers they receive from partisans on either side.A sort of code has developed--a jargon among debaters--that doesn't really help newcomers very much. And surprisingly, a lot of people are still showing up who are new to all this. Talking about RC vs. CA in the context of paleoclimatic temperature reconstructions does not mean too much to people who have never heard of the weblogs Real Climate or Climate Audit, nor of the tension that exists between them.They say in baseball that you can't tell the players without a program, and as yet there is no program. Given the structure of this site, I'm not sure that's a problem I can solve, although I will give it some thought. For now, though, I think identifying the important questions that remain unsolved is the best I can do for newcomers.Sensitivity: Most of us accept that doubling the concentrations of CO2 in our atmosphere will raise global temperatures by one or two degrees Celsius. But what happens to the rest of the atmosphere as it copes with this rise? The consensus holders, championed by Al Gore and James Hansen, believe that especially water vapor, another greenhouse gas, will increase and add its own contribution to global warming. Skeptics believe it will remain relatively unaffected.Consensus holders believe that their computer models, which captured the effects of the Pinatubo volcanic eruption quite nicely, tell us that sensitivity is about 3 degrees Celsius (with a generous plus or minus). (A sensitivity factor of 3 means that 1 degree of warming caused by CO2 will cause a total of 3 degrees of warming.) Skeptics say that without a piece of physical evidence, consensus holders are being very premature.Oceans: The oceans are a sink for both heat and CO2. Heat gets stirred into the ocean at a local level, interacting with salinity to create layers of differing heat levels at different levels. The oceans transport this heat and release it at odd times and odd places, helping cause phenomena like El Ninos and La Ninas. When the oceans warm, they release CO2. When they cool, they absorb more of it. (At least that's simple.) And the oceans hold a lot more CO2 than the atmosphere--93% of the CO2 shared between ocean, plants and atmosphere is in the oceans. It also moves through different layers of the ocean and can eventually be absorbed by microscopic organisms and turn into limestone at the ocean floor. Before that happens, though, it works at making the ocean slightly less alkaline, or more 'acidic.'But we really don't know what's happening down there. We know more about the moon than we do the ocean, in all honesty. (Well, we should--not as much is going on up there.) We don't know if the oceans are going to keep taking in all the CO2 we can belch out (but probably not) or if it will reach a point where it gives a lot of it back, which would be unwelcome indeed. We don't know if the extra CO2 we are emitting is going to have a huge effect on the alkalinity of the ocean, or a very small one. This is not to say that there are no coherent theories--there are, and the level of uncertainty is being reduced quite quickly. Which means within two decades or so we'll really have a good handle on it. (And while we're on the subject of oceans, when they warm, they expand and sea level rises--which it has been doing for quite a while, although there is disagreement on whether the rate of rise is increasing or not.)Clouds: Sunlight can bounce off the tops of clouds and go back into space. Clouds can cool the atmosphere. Clouds can trap heat underneath them. Clouds can warm the atmosphere. What's the net effect of clouds? We don't know. This is a big obstacle to understanding what's happening in the ol' global warming thing. Any one of these factors--sensitivity, the role of the oceans or clouds, could completely swamp other factors in determining whether global temperatures will rise or fall. They are that important. If all three swing in one direction it will be decisive without any question. Even if two end up being rather neutral, the third one--whichever one you choose--can swing the balance in either direction.Because we don't really know the answers to these big questions, you would think there's not too much to fight about. You would be an optimist. The consensus holders believe that the situation is so dire that we can't wait for the final figures to come in before we act. The skeptics disagree. And there is even a group in the middle (I am one of them) who think there will be some global warming, but it won't rise to the level of a catastrophe.As newcomers tour the blogosphere, they will encounter people who claim to know the answers to these questions. And certainly someday someone will come up with the right answers. But I would advise newcomers to beware those who are extremely confident and certain on these issues.