Saturday, March 24, 2007

IPCC: Global Warming "very likely" caused by humans

The recently released IPCC report on climate change, which reiterated the 2001 report conclusion that global warming was a real threat but upped the ante on human causation (from “likely (60% sure) to “very likely” (90% sure) was remarkable in many ways. Most usefully, it was unanimously accepted by the member countries, including the U.S., which for all practical purposes moves the debate forward from agreeing that there’s a problem to what’s the solution. And the report dragged the naysayers along with it, shifting their tactics from “it’s not happening” to “we can’t fix it.”

The downside is the price the IPCC paid to get that unanimity. Don’t get me wrong, I think the unanimity was hugely important to shift the debate focus. But now we have to deal with the scale and urgency of the issue, both of which were downplayed in the report. How? To get unanimity, they excluded any recent evidence that hadn’t formerly been incorporated into the climate models (i.e. had any degree of uncertainty about it). Two worrisome exclusions: feedback loops and extremes.

Feedback loops: we’ve known for years now that the farther you move from the equator, the more severe the warming. Evidence shows that the poles are warming up to five times faster than the global average. One reason is certainly this feedback loop: warming temps cause more ice to melt. Since ice reflects 90% of the sunlight (and heat) and whatever’s under the ice reflects a lot less, a net loss of ice means the earth’s surface warms more that it otherwise would. Warmer surface means the ice melts even faster, which uncovers even more of the heat-absorbing land/water, and so on. With a feedback loop, the changes aren’t linear, they accelerate. Unfortunately, our climate models are mostly still linear, so they are no doubt underestimating the scale of the problem. What’s true is that scientists still can’t precisely say how much they’re underestimating the problem, so they can’t come up with an equation for the climate model that could get general agreement.

Another loop: the rapidly warming northern tundra is causing the permafrost to melt. Trapped in the permafrost are huge amounts of methane, a gas that is 20 times more potent than carbon dioxide. As this gas is released, and its being released at an alarming rate, it causes accelerated warming, which in turn melts the permafrost faster, etc. etc.

Extremes: The other great omission is the extremes. The IPCC report mainly limited itself to global averages. It’s not the averages that will kill us first, it’s the extremes. An ‘average’ rise in sea level means a lot more to an inhabitant of Bangladesh than to a Midwest farmer. A small “average” global rise in temperatures masks the fact that in the Arctic and Antarctic, temperatures are rising much more dramatically, balanced by much smaller increases at the equator. The effects of climate change aren’t going to be uniformly felt: the higher latitudes will experience much higher rainfalls (warmer atmosphere holds more water), but in the subtropics they will be experiencing much lower amounts, exacerbating endemic drought conditions.

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