Monday, March 26, 2007

Where's your certainty?

Another recurring theme from people who argue against the fact that humans are changing the climate is a big focus on uncertainty. They are critical of forecasts of future temperature increases from complex climate models run on massive computer arrays. The models require simplifying assumptions to be computable, and they argue these assumptions could be "rigged" to make the models artificially confirm global warming.

Yet somehow, each of the rival proposals that they latch onto are excused from this scrutiny. They talk about galactic cosmic rays (GCRs) or solar variations as though we had clear, indubitable data showing these are the "real reason" behind recent temperature trends. In fact, neither of these external forcings is at all well characterized; we are far from having any clear basis for projecting long term trends in either one.

Then there are economic forecasts. Critics of the Kyoto accord regularly project "catastrophic" economic harm if the CO2 reduction targets are implemented. They are quite adamant about this; they seem certain of these projections. Yet the academic literature on this question tells a different story. The recent Stern Report is only the latest instance. Quite a while earlier there was Robert Repetto and Duncan Austin, The Costs of Climate Protection: A Guide for the Perplexed [World Resources Institute, 1997. 60 pages. ISBN 1-56973-222-1, 60 pages] link.

This document looks at projections made with several different economic models, and how much impact on GDP growth there could be if greenhouse gas reductions are implemented. They focus on seven key assumptions, and assess how strongly the outcome depends on each one. For each issue, they look at a "worst case" and "best case" assumption, and work through how much GDP growth would be impacted if all seven are for the worse, or if some or all are the better case. If all seven are in the negative--a "worst worst" case--the models project a significant hit to GDP, something like 7% less GDP growth over the time span needed to reach a 60% cut in emissions. That's not minor, but looked at in context, it is a reduction in foreseen economic growth (something on the order of a doubling of GDP over several decades.) If this takes 30 years, that's the difference between 2.1% per year and 1.9% per year of growth. The growth that would have taken 30 years might now require 33. Catastrophic?

But that's only the "worst worst" case; if even two of the seven factors turn out to the better, the projected impact shrinks to just a 2% hit to GDP over the whole interval. Then the annual growth is 2% vs. 2.1%.

If four of the seven factors turn out favorably, the impact is projected to be very near zero. Once five go favorably, mitigation turns out to be a net benefit to the economy! Some catastrophe.

Of course there are probably many serious studies proposing that greenhouse gas mitigation will be terribly costly to the economy. I won't try to claim that economists can give us a single, persuasive forecast of what's going to happen. There's plenty of room for debate over the economics. Repetto and Austin is already dated, but the Stern Report brings the issue up to the present with much the same import.

It's only the science that's so clearly worked out. We really can't say for sure what will develop economically over the next century. But some critics seem to want to have the reverse: the economics is settled, on the side of catastrophe if Kyoto is implemented; but the science is still cloudy. So we show forget the "Precautionary Principle" and keep stalling. They have everything backwards.

Friday, March 16, 2007

And thanks for all the fish...

"Oh, no! Not again!" is the reaction of a bowl of petunias materialized as a side-effect of a passing spaceship powered by Infinite Improbability Drive in The Hitch-hiker's Guide to the Galaxy. The petunias find themselves high above the planet, and thus doomed to a brief lifespan of plummeting. We're left puzzling over how many times the petunias may have been put through this brief and pointless plunge.

This could well be the motto for anyone running across a global warming denier as well. I'm constantly struck by how often the exact same seemingly obscure "objections" are raised by ordinary people - regular folk, outside the hothouse of academia, who don't seem like the type to sit about reading up on galactic cosmic rays or paleoclimatic reconstruction. The selection of odd topics just keeps repeating in a most suspicious way.

I'm attending a course on the physics of radiative processes in the atmosphere (okay, so I am enfolded in the hothouse of academia). Chatting before class this morning, our prof mentioned having given a talk on global warming to grade 5 class. The kids had viewed An Inconvenient Truth and were now quite concerned.

The odd part was that one of the parents attended the talk and make it clear he is a full-out climate change naysayer. He interjected with a few rather technical questions, then buttonholed our prof for half an hour afterward. Apparently one of his issues was galactic cosmic rays (GCRs).

I don't know what sources this guy was working from, but it's fairly easy to imagine. There is no shortage of partisan websites which exist to collect new ways to argue against the reality of global warming, or at least trying to avoid human responsibility for it. They tend to engage in scientific "cherry picking," jumping on any publication or media statement by any scientist that could be either used, or twisted, in their campaign of denial.The flavour of the month is GCRs. Before that it was changing solar output as expounded by, e.g. Russian solar physicist K.I. Abdusamatov.

If you want a detailed account of what these are all about, and why they don't in any way refute the reality of human-induced global warming, I'll recommend RealClimate as a great resource. For my part, I'll just point out that in any of these "alternate explanations" of recent temperature changes that I've checked out, none have even attempted addressed the basic point that we know CO2 traps heat, and we have a good idea how strongly it affects climate. There are facts of basic physics that form the basis for the theory of the greenhouse effect and the role of CO2 as well as methane and other human additions to the atmosphere like CFCs.

Now, I'd say it's simply undeniable that humans are the cause of CO2 concentrations having risen suddenly to levels unseen for a million years or more. It's also unreasonable to suggest that we are not headed for a doubling or more over pre-industrial levels, barring a major reduction effort. The physics of the greenhouse effect tell us that this much additional CO2 will inevitably force a hotter climate.

So if you want to argue that CO2 is not already warming the planet and that higher levels in the future won't lead to more warming, it's not enough to say "I've found another outside forcing factor." Mainstream scientists using basic physics and spectroscopic measurements have worked out a figure known as the "radiative forcing" for a doubling of CO2 concentrations. The typical denial argument skips over this issue, implying that the forcing factor is zero or near zero. There is almost never any justification for that departure from the scientific literature. Richard Lindzen takes this tack, though at least he allows a non-zero value--something like 0.25 W m-2 versus the consensus value of about 3.75 W m-2. Lindzen at least gets points for giving his own number, but most denialists simply dismiss all this physics out of hand. The latch on to some new proposed candidate like GCRs or solar variability as if these could simply erase the existence of the greenhouse effect.

The point is that we have a clear theoretical handle on how and why CO2 absorbs infrared radiation in the range of the spectrum where the earth and atmosphere radiate strongly. This comes from hard science with precise laboratory measurements, as well as lots of ground- and space-based observation. This area of hard science provides a basis for predicting how much more heat we will trap by a given rise in CO2.

Saying there are other external forcings as well (solar variation, GCRs) says nothing to change these facts. Yet the denial movement regularly trots out these red herrings as if they somehow showed there is no greenhouse effect. The correct response to a proposed new forcing is to treat it in context of all the other forcings that have been so well covered in the IPCC assessment reports (ARs). Solar variation barely shows up on the chart; GCRs are too new a theory to have been covered in existing ARs; we'll have to wait to see how the dust settles on this new proposal.

But please be clear that this is all we have so far: a new proposed external forcing factor, which if confirmed (far from a certainty), would just have to be superimposed on all the existing forcings we have already identified and quantified. A new forcing does not wipe away all the others. Each known forcing has been assigned an error bar reflecting the remaining uncertainties over their exact values. A few are still poorly understood, but the forcings for CO2, methane and CFCs are fairly tightly constrained (unless you ask Richard Lindzen).

Next month, expect the denialist websites to latch on to some new claim, raising whatever it is to the level of a sure thing, and suggesting once again that this one means we can forget all about any greenhouse effect.

The non-sequiturs just keep rolling.

Oh, no! Not again!

Thursday, March 1, 2007

Does anyone still doubt whether humans are changing the climate? Well, unfortunately...

Last month the IPCC released the Summary for Policymakers (SPM) of their Fourth Assessment Report (AR4); the full report is due out this Spring. I was really struck by the change in tone of the media coverage in the wake of this document, coming on the heels of the Stern Report and the big audience response to Al Gore's film "An Inconvenient Truth." Up until this past month, a lot of media coverage of global warming fell victim to a "he said, she said" format where global warming proponents and deniers were given "equal time" in the interest of supposed "fairness." But after the release of the AR4, across the board I kept seeing media headlines saying that the debate is "finally over." Mind you, the scientists knew this some time before the media caught on; but at least now they have taken note.

Strikingly, both the Bush White House and Canada's Kyoto-defeatist minority Conservative government both went on the record as conceding that humans are changing the climate. Even John Howard's Kyoto-rejecting administration in Australia has given up questioning the human role: "I am not as fanatical about it as others," he said. But, "the accumulated evidence is undeniable ... we do have to reduce greenhouse gas emissions." [International Herald Tribune, January 25, 2007] link

All this is quite new. These were the last three G8 leaders who were playing both sides of the fence on the science until recently. Harper in particular got slammed after his recent epiphany on climate science, as the Liberal party found a copy of a fundraising letter he sent out in 2002 calling Kyoto a "socialist plot" and touting "tentative and contradictory scientific evidence about climate trends." But the opinion polls showed a strong surge in public concern over global warming, so Harper had to give ground.

Once the AR4 SPM was released, the media flashed the "debate is over" headline, then spent a good ten days summing up the science. The Globe and Mail ran a two-page centre spread with a map of Canada's projected climate by 2099 - the map showed isotherm lines of mean temperate rise, with Toronto inside a +6C contour. Wow.

I take this to mean that the scientific "debate" in the mainstream media can now be framed as settled, instead of "he said, she said." Journalists are in effect giving themselves permission to point to the IPCC as the received wisdom, instead of having to bracket it with opposing views. This will certainly save them time.

Looking around the internet over the past few weeks, it is starting to look like a lot of the deniers have not yet received the memo that the debate is "over." Blogs and discussion groups continue to roll with back and forth over such profound topics as a debate on whether the scientists of the IPCC (and the NAS, AAAS, Britain's Royal Society, Swedish Royal Academy, ...) can or cannot be called a "consensus." If they can, deniers next say that science "does not operate by consensus" (so, what? Now we have too many scientists in favour? Oy vey!) Perhaps they also claim the missing scientists on side B of the "debate" have been driven underground by the other scientists not being nice to them.

If you try to work through the logic of the greenhouse effect with some of the deniers, they may throw stones at every step in the chain of reasoning. A lot of times the exact same very specific debating points will turn up over and over from different people in many different forums. There's a great "taxonomy of skepticism" on the wonderful blog A Few Things Ill Considered. I'm afraid I've seen almost all these objections tossed out more than once - each one refutable, but there is such a litany of them.

A lot of these points have been hammered repeatedly in the op-ed pages of conservative newspapers like Canada's National Post. So I guess it's no surprise that I also encounter the "man in the street" following virtually the same script as the online debating club crowd. Last week I spoke to someone I hadn't seen in some time. When I mentioned I was taking a university course on global warming, he started posing a series of questions that could have come straight from the Ill-Considered skeptic's checklist. He was very polite, and I gave my best short responses to them one by one. After the seventh or eighth "but what about" question, I had to stop myself from asking what editorial page he had been reading. The deniers have been quite effective in getting their program of doubt across to the public.

So it looks like so far, the message has not reached all the foot soldiers in the trenches that the climate denial army has been forced to surrender. Should we be dropping leaflets, perhaps?

Of course, the end of one debate, over the science, leads inevitably into the start of another, over the politics: what shall we do now? That's the right place to be in the discussion. But for the deniers, they have a Plan B response that may startle you. As the "scientists can't agree" objection gets worn away, a lot of opponents are quickly switching their tune to "it's too late to stop global warming." Whew - that was QUICK, eh? Last week you said it wasn't even happening, and now suddenly it got away from us? In two weeks?

I've read a string of pieces by opponents of Kyoto this week arguing that climate change is now inevitable, and mitigation (lowering our CO2 emissions) sufficiently is impossible, so we all need to brace ourselves and start planning for how to cope - so called "adaptation."

The flaw in this argument is that we can't afford to give up on the mitigation front; however poorly you feel about our prospects for keeping CO2 levels from soaring, it's absurd to say we should not even try, and just sit back and prepare for all the consequences. The impact of CO2 is not just linear - there are good reasons to be concerned that as levels rise, new and more serious consequences come to bear.