06 October 2014

Our Understated Climate Problem

For climate disease, there is no doubt remaining about the diagnosis: global overheating, mostly from an insulating blanket of the carbon dioxide produced by burning fossil fuels. That’s what stirs up such knock-on effects as extreme weather and expanding subtropical deserts.

It's now dishonest to claim that the overheating hypothesis fails, just because some line of evidence seems dubious to you. Even if you were right to be suspicious, there would still be a dozen independent lines of evidence, all firmly pointing at global warming destroying the climate that supports 7 billion people. Anyone still dubious about global warming immediately labels themselves as either a quarter-century out of date or a profit-making promoter of climate confusion.

The climate scientists’ forecast is also impressive–so far as it goes. However, their state-of-the-art climate simulations leave out components where they are not sure enough about the numbers. "When in doubt, leave it out."  Vicious-cycle feedback loops were originally omitted as insufficiently understood.

When only the slow accumulation of heat-trapping gases are included in simulations, it’s no surprise that they show the heat waves slowly getting worse.

But what’s left out of most simulations are the equally important rapid change mechanisms, where good numbers are still hard to come by. “Are you really, really sure?” pressures have only aggravated the experts’ understatement of our climate problem.

A familiar example of the forecast's incompleteness is the loss of Arctic summer sea ice, long predicted to disappear sometime after 2100. Instead, the track record since 2000 suggests the ice might disappear in the next decade. Obviously, something was left out of the simulation forecast. The Arctic overheating is already causing strange winter weather farther south.

We also cannot count on gradual transitions like the ones seen in current climate simulations. When forced to move, climate can jump into a new regime with no warning. For example, the world drought acreage suddenly doubled during 1982 and has never gone back . It does not require a sudden jump in temperature to trigger such a change-of-state transition.

What makes them sudden? Vicious-cycle feedback loops are often involved but a shift in the winds will suffice. Air and ocean circulation patterns can radically shift in mere months (a big El NiƱo is the classic example). If you live somewhere that fails to get its usual wind-borne delivery of ocean moisture, you will experience drought, wildfires, and crop failures. Somewhere else, they get flash floods and soil erosion. In human terms, one region's loss is not another's gain.

No one has a clue about when additional climate jumps will occur as the overheating continues. The obsession with precise numbers usually causes the subject to be omitted from the climate forecast.

Is this “scientific understatement” wise, when it amounts to seeing fire but reporting smoke? Physicians would not omit a warning simply because they couldn’t attach reliable numbers to it. Using the slow-only simulations as a forecast is grossly inadequate to the task of warning the public and policymakers of the dangers ahead.

Thus the typical climate forecast ought to be firmly labeled “At least this bad but probably worse.” And probably sooner, too. We must bear in mind that the extreme weather episodes that are forecast for 2028 could happen this year instead.

William H. Calvin is a professor emeritus at the University of Washington’s medical school in Seattle and the author of Global Fever: How to Treat Climate Change  (University of Chicago Press, 2008). The latest version of the CO2 cleanup was a finalist in MIT's 2013 climate contest.

September 2014    WCalvin@UW.edu      faculty.washington.edu/wcalvin

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