Are crocuses in January a sign of the apocalypse?

weather-map.gifThe cherry blossoms are blooming in Brooklyn. Golfers are hitting the links in Chicago. Ski resorts and ice fishing competitions suffer, while wineries and ice cream makers celebrate. 2006 was the hottest year on record. Even the staunchest global warming denialist must admit that the end times are nigh.

But wait! San Francisco is experiencing record cold, prompting a state of emergency. Blizzards and avalanches are hitting the middle of the country. And no less an authority than the National Weather Service has declared that the recent warm temperatures have nothing to do with global warming. Blame El Niño instead.

So which is it? Is the warm weather a direct result of global warming, of El Niño, or of some other unknown phenomenon?

The short answer is: who knows?

A longer answer is that it’s important not to confuse weather and climate. Climate refers to a broad set of conditions that characterize the atmosphere over decently long periods of time. Weather is a snapshot of those conditions at any one instant. Although the two are clearly related, the relationship is indirect and statistical. It’s not possible even in principle to trace back a single weather event to any distinct cause.

An even longer answer can be found on the ever-helpful and clear-eyed RealClimate, which digs into the recent weather patterns with gusto and finds all of the media-hyped explanations wanting.

On the one hand, the Weather Service overstates its case when it ascribes all of the recent temperature spike to El Niño. For one thing, last winter was also anomalously warm, and at the time there was no El Niño. (In fact, we experienced its opposite, La Niña.)

Also, the current temperature spike is about five times the effect of a typical El Niño. Taken together, these issues do strongly suggest that forces beyond just El Niño are at play.

Further, the patterns of warm weather fit very well with those predicted by models of manmade climate change. So do we have our smoking gun?

Not really. For one thing, the weather has been way too warm lately to be directly attributable to global warming. Recall that most climate change models predict an average warming of a few degrees over the course of the next century. A spike of 20 degrees over the course of a single week isn’t climate change. It’s a freak event.

Which is basically what all weather is: a momentary circumstance reflecting a chaotic and indeterminate set of atmospheric conditions. The most that can really be said is that both El Niño and manmade global warming make the type of warm weather we’re presently seeing more statistically likely than it otherwise would be.

Beyond the general wonkery, there is an important point here. It’s important not to get overly caught up in individual weather events, because the temperature pendulum is going to swing around quite a bit even as average temperatures gradually increase due to global warming. If overly much is made of every warm spell, skeptics are going to play the same game in reverse, turning every cold snap into another argument for inaction.

Another important, but easily overlooked point is that climate change is about much more than just warming. As a resident of New York, I can personally attest to the fact that the current warm weather happens to be extraordinarily pleasant. But climate change — which we can take as a shorthand for species extinctions, extreme weather events such as hurricanes, drought, flooding, food supply disruptions, population dislocations, and a whole host of other effects — will not be pleasant.

As always, it’s important to keep the big picture in mind.

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