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Is This the New Normal?

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I'm not the only one who is pondering the extreme weather we've been having in the U.S. this summer. Pick up any newspaper or read pretty much any news magazine and there's discussion of the extreme heat waves we've been having in the continental U.S.

At my Colorado field site, the snow melted a month earlier than normal, and the marmots I study emerged earlier than ever. That is the ones that survived. You see, marmots hibernate, and to successfully hibernate, they need a good "blanket." Snow provides the "blanket," and there wasn't much snow last winter (it was an exceptionally warm and dry winter), so we had what probably could be described as extra mortality from a winter drought.

In addition, it hardly rained at all in May and June, and the vegetation is much less verdant than I've ever seen it. These tinder-dry forests and meadows exploded into firestorms in the Colorado Front Range, but locally we were lucky. And now it seems we've finally got some seasonal precipitation that should forestall a summer drought. And this is important because we know that summer droughts are really bad for marmots. Fingers crossed.

But this isn't what has me pondering the current weather. A month or so ago, at a dinner party with some friends in L.A., my dad asked a climatologist colleague of mine about warming trends and storms. The one thing he said was that as the Earth warms, we'll have more extreme events; it's a statistical inevitability, given that the entire range of temperatures is shifting to the right.

A statistical inevitability. So what does this really mean? It means that what we previously viewed as big storms will be dwarfed by even bigger storms, and what we previously viewed as extreme heat waves would be dwarfed by even hotter heat waves, and what we previously viewed as extreme droughts will be dwarfed by even more extreme droughts. The new normal (in the sense of average storm intensity, temperatures, and rainfall) will shift a little, but the new extremes will be even more extreme.

For marmots (and other animals and people), this probably isn't too good. Why? Because many organisms are adapted to a relatively narrow range of environmental parameters (temperature, rainfall, humidity, etc.), and we assume that not only has natural selection acted on the average parameters, but to some extent there may be some buffering built in to cope with even greater variation. Change those parameters a little, and perhaps there will be sufficient flexibility (or what we call "phenotypic plasticity," in biological jargon) to respond to the change. But change it a lot and you risk a big die-off, because animals (and plants) have not evolved to be sufficiently flexible to respond to the new extremes.

Thus, it isn't the incremental changes in temperature associated with global warming that will necessarily have the biggest immediate effects; rather, it's that statistical inevitability -- the even bigger extreme events -- that will cause massive die-offs.

Ponder this as you're relishing the declining temperatures from the waning heat wave. The new normal will be more extreme.

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