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Weather on Steroids

By Ben Strauss

It's opening week of baseball, and possibly the hottest one ever in the nation's east. That gives me a perfect excuse to share my favorite analogy for talking about climate, weather, and warming. If you can understand some basics of the great American pastime, you can understand a lot about climate science, including a paradox that confuses commentators again and again, most recently CNN meteorologist Chad Myers. Namely: if we have such a hard time predicting the weather a few days from now, how can we say anything about the climate in future decades?

To get at the answer, we must begin with the difference between weather and climate. Weather from day to day is fickle, like a few swings or at-bats. Can you confidently predict how A-Rod will hit tomorrow night? It's hard to know how he'll be feeling, or if a heckler will get under his skin.

On the other hand, you can probably make a safe bet he will have a high season batting average — because his skill will shine through when you add up all the swings. That is like climate, the accumulation and average of weather.

You could guess wrong on every swing, and guess about right for the season. In the same way, a meteorologist could scramble the Phoenix forecast every week, but still confidently predict it will stay a hot place.

So what about climate change? Climate change means weather on steroids.

Consider the case of Mark McGuire. He would surely have hit many home runs without using drugs. But so many? The extra muscle and power he got from steroids should have increased the chance that each fly ball would make it out of the park. McGuire still made strikeouts, ground balls and bloopers; he just hit more long balls. It would be hard to attribute any one of them to steroids — but added up, they sure seemed unusual.

The same principles apply to injecting the atmosphere full of greenhouse gases. The gases trap heat — like more muscle for weather. We still have cold days and seasons, but on average there are more warm ones. It is hard to attribute any one hot spell to climate change — but if you add up the whole pattern, something unusual is going on.

This week, high temperatures equaled or exceeded more than 1000 records across the US, according to the National Climatic Data Center. In fact, an occasional week like this isn't far out of the ordinary; but it does form part of a larger pattern. A 2009 study found that recent years have seen double the number of new highs as new lows (my Climate Central colleague Claudia Tebaldi contributed to this research). If the planet's average temperature were holding steady, we would expect the numbers to be about the same. Instead, the discrepancy fits with global warming.

In my last post, I suggested that commentators err by reading too much from single instances of unusual cold or heat, like the late Arctic freeze this year or the arrival of July heat in April. But I also added a small asterisk. In the context of a warming planet, and the gap between record highs and lows, almost any new low temperature event would need a whole lot of company before it could change our scientific interpretation of things. New temperature highs generally shouldn't change our interpretation, either. But, by contrast, they do reinforce a growing preponderance of evidence for warming.

There's another part of the asterisk, too. By increasing power, steroids may lead not only to more home runs, but also to longer ones. The longer the home run, the more likely it would happen with steroids, as compared to without. In much the same way, the farther a heat wave deviates from normal, the more it should increase our belief that an extra factor is at play — like global warming. The European heat wave of 2003 was one such strong example.

Baseball can be played with or without steroids, and we can choose how much carbon we send into the atmosphere. Understanding the parallels could help us make more informed decisions.

Gallery

Longer Heat Streaks Across the U.S. The length of annual heat streaks — the number of consecutive hot days — is increasing in these cities.

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