How bad can it get?

OK. I've had enough. The "at an alarming rate" stories on the latest climate change research are beginning to spiral out of control. This one, from the Canadian Broadcasting Corporation, was the last straw:

Residents of Iqaluit and Pangnirtung have been stowing away their parkas and kamiks this week and pulling out raincoats. Warm temperatures and rain showers across southern Baffin Island have broken almost every record on the books. "The snow is melting off the roof, I can't believe it, it's unreal," says Iqaluit resident Dennis Shappa. "If it freezes over, you know, caribou are going to have a hard time getting to their source of food," says a concerned Moses Kilabuk. (CBC, Feb. 28.)

For those not familiar with Iqaluit and Pangnirtung, they're up near the Arctic Circle. I've been there in the spring. Rain is not normal.

In other news:

The Antarctic ice sheet is losing as much as 36 cubic miles of ice a year in a trend that scientists link to global warming, according to a new paper that provides the first evidence that the sheet's total mass is shrinking significantly. (WaPo, March 3)

and

Greenland's glaciers have begun moving faster, almost doubling the rate within the last five years at which they dump ice into the Atlantic Ocean, new satellite images reveal. The data has sparked warnings that experts have underestimated how much sea levels will rise in the future. (New Scientist, Feb. 17)

and

... scientists will say there is still great uncertainty about the pace and scope of future change, although by the end of the century global temperatures could increase by up to 5.8 C. (BBC, March 1)

Meanwhile, James Lovelock in his new book The Revenge of Gaia says the Earth is

seriously ill, and soon to pass into a morbid fever that may last as long as 100,000 years. I have to tell you, as members of the Earth's family and an intimate part of it, that you and especially civilisation are in grave danger.

But wait. It gets worse. I recently got ahold of a paper on long-term climate change -- we're talking about the next 1000 years, not just the coming century -- that will appear in Climate Dynamics.

The authors of "Millennial timescale carbon cycle an climate change in an efficient Earth system model" (DOI 10.1007/s00382-006-0109-9), three British researchers and one Canadian, calculated what would happen if we burn all the fossil fuels available on the planet. Their most extreme scenario has the world 12.5 C warmer (about 23 F) than it is now. Other side-effects of our addiction to oil include

complete Greenland melt by the year 3000, 10 m of ongoing sea level rise, possible collapse of the Atlantic meridional overturning circulation, a 1.15 unit drop in ocean surface pH, huge loss of global soil carbon and dieback of some tropical and subtropical vegetation.

And so forth and so on.

Of course, that's just what the scientists say might happen. In a worst-case scenario. The good news is if we left the unconventional reserves of oil and gas in the ground, we'd be able to keep the temperature increase down to 7 C or so. But that's still disastrous for beachfront property owners in Florida, most Bangladeshis, and anyone who wants to eat in Africa, among others content with the status quo.

But how much skepticism should be applied to such long-term predictions? I say give them no mind. Not when the near-term is already so troubling. Consider that just about everyone agrees that, thanks to the time it takes between the emission of greenhouse gases and the consequent warming effects they will induce, we're already pretty much committed to a certain amount of warming. And I'm thinking we should be working hard to nail down just what that guaranteed warming effect will be before we worry about AD 3000.

The consensus is shaky. Take that reference in the BBC story to a 5.8 C rise. That number is what some climatologists believe might be the result of doubling the amount of carbon dioxide in the atmosphere, (compared with pre-industrial levels), something that will probably happen no later 2050, even if we all start driving Priuses next week. It's a number that may or may not be included in the next report from the Intergovernmental Panel on Climate Change.

Not everyone is convinced that number is realistic. The conventional range for the effect of doubling CO₂ used to be a little lower -- 1.5 to 4.5 C. But along with all these new reports of melting glaciers and rising oceans and dwindling crop yields, some researchers are increasing the odds of reaching higher temperatures sooner than later.

Climatologists James Annan and J.C. Hargreaves are having none of it. Their new paper, "Using multiple observationally-based constraints to estimate climate sensitivity" won't be officially published for a few weeks, but a PDF is here. In the paper, they peg the "climate sensitivity" of a 2 X CO₂ world at just 3 C. They conclude:

Even with generous uncertainty estimates, a value greater than 4.5 C seems very unlikely. In fact, our implied claim that climate sensitivity actually has as much as a 5% chance of exceeding 4.5 C is not a position that we would care to defend with any vigour, since even if it is hard to formally rule it out, we are unaware of any significant evidence in favour of such a high value.

I have no idea whether Annan and Hargreaves' methods are better than those being used to generate plausible scenarios that top 4.5 C. Annan, writing in his blog, anticipates some controversy. "As recently as last summer," he says, "I was happily talking about values in the 5-6 C region as being plausible, even if the 10C values always seemed pretty silly." And furthermore

The paper didn't exactly sail through the refereeing process, but has now been seen by a lot of researchers working in this area. Although many of our underlying assumptions are somewhat subjective, our result appears very robust with respect to plausible alternatives (this was rather a surprise to us). No-one has actually suggested that we have made any gross error (well, some people are rather taken aback at a first glance, but they have all come round quickly so far). It's important to realise that we have not just presented another estimate of climate sensitivity, to be considered as an alternative to all the existing ones. We have explained in very simple terms why the more alarming estimates are not valid, and anyone who wants to hang on to those high values is going to have to come up with some very good reasons as to why our argument is invalid, coupled with solid arguments for their alternative view. A few nit-picks over the specific details of our assumptions certainly won't cut it.

The moral here is not that climate experts are still arguing, although they are. It's that they're putting a lot of effort into arguing over a couple of degrees centigrade. And while I doubt you'd get too many climatologists to admit it (to them, 2 degrees is a lot), they're now getting deep into hair-splitting territory, from a public policy perspective.

Even 3 C will make more a very different world than the one with which we grew up. Never mind the worst-case stuff. If the moderate, non-alarmist predictions are calling for such a future, then we are in for some very interesting times indeed.