By Ben Strauss
As Eastern states bask in July heat this week, the National Snow and Ice Data Center has reported a record-late freeze in the Arctic. And this winter, the Arctic was unusually warm — as we shivered through record snow in parts of the US.
Why can't the planet be simpler — if it's warming, just warm up, and if it's cooling, just cool down? Everywhere, and all the time?
A number of commentators have seized on the late seasonal growth of Arctic sea ice this year — and, earlier, on the colder than normal American winter — as evidence against climate change. I haven't seen anyone using this week's record-breaking heat yet as part of the case for warming, but I wouldn't be surprised to find that, too.
It's well known that people like to pick out information that supports the views they already have — a weakness most of us share. But is there any scientific merit to the arguments that March's Arctic ice, plus the cold winter here, disprove warming? In a word, no.
To begin, there is no evidence for a big rebound in Arctic sea ice. It has been rapidly getting thinner and shrinking in area covered for decades, while the Arctic has warmed faster than any other region. The current commotion is about the peak annual area of ice covering the Arctic Ocean, just before the warm season melt-back begins. The maximum this year took place late, on March 31, but — contrary to what you'd expect given the attention — average March coverage was less in area than 2009 or 2008. While all three years did exceed the record low level in March 2006, year-to-year changes are mainly a distraction. What matters most is the long term trend — and, at least since 1979 (after satellites started watching routinely), the long term trend for March (and every other month) has been for less ice.
So, what about the cold winter here in the US — is that evidence against warming?
To weigh the question, it helps to consider another. If the temperature is below normal in New England, does that mean it's also cooler than average in Australia?
Winter 2010 was unusually cold in much of America, and in Siberia and parts of Europe, too. It was unusually warm about everywhere else — and, on average, globally. In fact, it was the fifth warmest winter ever recorded. The world's temperature can't be taken with the thermometers in one nation.
The moral of this story is that one place does not make an average, just like one year does not make a trend. Consider this analogy: does the performance of one stock, or even sector, dictate the performance of the whole market on a given day? And does the performance of the market on one day, or in a month, tell you whether the long term trend is bull or bear? Would you make major investment decisions based on such narrow or short-term information?
Your answer, I hope, is no. We shouldn't judge the market based on one stock or day. In another comparison, we shouldn't judge a sports team based on one player or game. And we certainly shouldn't evaluate climate change based on the weather outside our door this week, or in the Arctic for one season.
There is a small asterisk to this principle in certain cases, which will be the subject of my next piece.