The weather doesn’t care how you feel about it. So the question of how you ought to feel about the weather—specifically, about the wave of warmth that covered the eastern United States this past weekend, and that promises to linger through Christmas—is a human question. What does a warm December signify?
One natural response is to find it creepy. Day after day, while cut firs crowded the sidewalk racks in New York, a thick tropical haze glowed in the air. Coats have gone back in closets; people have sweated. Always Christmas but never winter. This is not right. If you are of a mind to worry about the warming of the planet, you might look at this and worry.
Alternatively, you can “enjoy it!” That’s the advice of Slate’s weather writer Eric Holthaus, who wrote yesterday that there was no point in worrying about it. “Global warming wasn’t primarily to blame/thank for this weekend’s ridiculously warm weather,” he wrote. Instead, the warmth is fed mainly by a “record-breaking El Niño” and the “lack of snow so far.”
Global warming, Holthaus wrote, is only responsible for “bumping up temperatures by perhaps a couple of degrees”:
Blaming an exceptionally warm December day entirely on global warming is just as misplaced as senators seeking to use a snowball as proof against it. Climate change made this weekend’s warmth more likely, but it wasn’t the main driving force.
Someone was making an argument worthy of a snowball-waving senator, here, but it was Holthaus himself. Sure, if you believed that global warming had officially arrived this past Saturday, in a sudden 22-degree surge past the old average temperature, then you should take his advice and calm down. You should also pull a chocolate egg out of your ear and eat it, or sprout wings and fly, because you are a ridiculous fictional construct and you might as well enjoy being one.
Take away the words “entirely” and “primarily” and there’s no dispute left worth having. When the parched West burns, the wildfire won’t be entirely caused by global warming. It will be caused by someone tossing a cigarette butt out the car window into a dry field, or by lightning striking a withered tree. Warming will have merely contributed to the conditions that made the fire possible.
A springlike warm spell in December is not any sort of decisive proof of anything. It is, however, a probabilistic result that is becoming more likely to happen as the planet warms up. A severe El Niño produces wildly anomalous warm weather in the East—but as Holthaus concedes, scientists expect severe El Niños to become more likely with global warming. The lack of early snow reinforces the warmth. Why hasn’t it snowed yet? It’s been warm.
This doesn’t make the case that global warming is real. There are global temperature measurements and ice-cap observations that do that. It is possible that two months from now, another polar vortex could come lashing down and freeze the Hudson River again from bank to bank for a while, and that won’t make the case that warming isn’t happening. It will be a little more data, and local data at that.
The probabilities influence the probabilities, and it adds up. The floods that came with Hurricane Sandy were not directly caused by rising sea levels. The sea is only rising about a tenth of an inch a year, and Sandy brought a surge about nine feet above high tide. But the rise of the sea will announce itself through ever more frequent separate incidents of flooding.
Taken in isolation, this sticky December would be nothing to worry about. The weather doesn’t happen in isolation, though. At a glance, the weather in New York this year wasn’t especially dramatic. The summer wasn’t so bad, was it? Only one day in the whole month of August reached 95 degrees. But no day in August had a high temperature lower than 81 degrees, either.
Overall, in August, there were 26 days when the high temperature was above the average high for the date, and only three days when the high was below the average high (the other two days matched the average). In September, 27 days were above the average high for the date, and only one was below it.
For the year as a whole in New York, so far, there have been 208 days with an above-average high temperature, and 127 with a below-average high. The warming trend is a thumb on the scale. The weird muggy holiday season isn’t disturbing because it stands so far out from the rest of the year. It’s disturbing because it fits in.