Like the Odds of a Heart Attack?

The limits of medical analogies for the climate-weather connection

With the latest death toll from floods in Thailand reaching nearly 400 people, reporters have had yet another opportunity to explore the connection between climate change and extreme weather events.

On Wednesday, the Los Angeles Times published an op-ed by Michael Lemonick, a senior writer for Climate Central, a nonprofit journalism and science organization based in Princeton, New Jersey. The bottom line, spelled out in the headline, was that, “Climate change doesn’t ‘cause’ massive storms or severe droughts, but it raised the odds.” In order to make that point, Lemonick introduced an analogy worthy of journalists’ consideration.

He compared Thailand to a heart attack victim who, before croaking, smoked, had diabetes and high blood pressure, ate a diet high in salt and saturated fat, didn’t get any exercise, and had a history of heart attacks in the family:

So what killed him? Most people are savvy enough about health risks to know this is a trick question. You can’t pick out a single cause. His choices and his genes all contributed to the heart attack — but you can say with confidence that the more risk factors that pile up, the more likely it is to end badly.

Somehow, though, people think that it makes sense to ask whether a given extreme weather event — a devastating heat wave or a punishing drought or a deadly torrential rainstorm — is caused by climate change.

That’s a trick question too. Scientists know that the increasing load of greenhouse gases we’re pumping into the atmosphere doesn’t “cause” extreme weather. But it does raise the odds, just as a diet of triple bacon cheeseburgers raises the odds of heart disease.

This is the same idea behind as the famous “loading-the-dice” analogy, and readers may find the heart attack frame more intuitive. Nonetheless, both analogies miss an important point: not only is there mounting evidence that climate change has increased the likelihood of extreme weather events, but there is also mounting evidence that it has increased the likelihood that those events will be more intense.

The New York Times’s Andrew Revkin addressed this point in a 2010 blog post titled “Climate Extremes: Beyond Loaded Dice.” He quoted Steven Sherwood, a climate scientist at the University of New South Wales in Sydney, Australia, explaining that:

The “loading the dice” analogy is becoming popular but it misses something very important: climate change also allows unprecedented (in human history) things to happen. It is more like painting an extra spot on each face of one of the dice, so that it goes from 2 to 7 instead of 1 to 6. This increases the odds of rolling 11 or 12, but also makes it possible to roll 13.

Evidence that climate change increases not only the likelihood of extreme weather events, but also the likelihood that they’ll be real record-setters, has piled up in the last two weeks. But it’s important for reporters to remember that the strength of the connection between climate change and extreme weather depends on the specific type of weather event.

On October 24, PNAS published a paper by scientists at the Potsdam Institute for Climate Impact Research. It described a new method for quantifying the link between long-term warming trends and heat records—for instance, concluding that there is an 80 percent chance that 2010 Russian heat wave would not have occurred without climate change. (The paper didn’t get much coverage beyond a well-done post by Wired’s Brandon Keim).

On Tuesday, The Associated Press and AFP shared details from a leaked draft summary of an upcoming special report on managing the risks of extreme weather. The report, from the Intergovernmental Panel on Climate Change (IPCC), says it is likely that climate change has already increased the frequency and/or intensity of heat waves, droughts, and floods.

As for the inundation in Thailand, in his op-ed for the Times Lemonick was careful to point out that the primary causes were an unusually heavy monsoon season exacerbated by the advent of a “king tide” (a twice-yearly global occurrence caused by an alignment of the Earth, moon, and sun). And the AP’s article about the IPCC report made the case that human factors beyond climate change, like “population growth, urban development, and river management,” also contributed to the crisis:

In fact, the report says, “for some climate extremes in many regions, the main driver for future increases in losses will be socioeconomic” rather than a result of greenhouse gases.

This point (explored in an October 13 New York Times article headlined, “As Thailand Floods Spread, Experts Blame Officials, Not Rains”) highlights another shortcoming of the heart-attack analogy. It is helpful to understand that dietary or genetic factors can both contribute to the odds of cardiac arrest, but doctors still need to treat patients. So the question becomes: are the symptoms mild enough that prescribing a bit of exercise will alleviate them, or is a more serious intervention like statins or a stent required?

You could try to extend the metaphor into the treatment of manmade climate change, but it quickly breaks down or grows too confusing to be useful. Reducing greenhouse gases, or climate-change mitigation, might correspond to better exercise, insofar as it would alleviate symptoms slowly (almost imperceptibly, at first), but systemically. Geo-engineering, or climate-change adaptation, might correspond to statins or a stent, insofar as it could (theoretically) alleviate symptoms quickly, but not systemically (and it might have deleterious side effects).

But that leaves out things like improved urban planning and sustainable development, or what might be called climate-change resiliency, as opposed to mitigation or adaptation. They’re sort of like exercise, insofar as everybody should be doing it as a matter of course. But they’re also like statins and stents, insofar as they alleviate symptoms quickly, but not systemically (not to mention that some elements of urban planning, like levees, are a form of geo-engineering).

If that seems befuddling, that’s because it is. Analogies like the one Lemonick suggested are great for helping readers understand some climate-weather concepts, like storm frequency and risk factors, but they struggle to explain others, like storm intensity and mitigation/adaptation options. So, while they are handy instruments in a journalist’s toolbox, reporters must also be mindful of their limitations.

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Curtis Brainard writes on science and environment reporting. Follow him on Twitter @cbrainard. Tags: , , ,