By Janet Raloff
Welcome to the new climate; it’s keeping those Weather Channel reporters pretty busy with field reports on everything from a crop-slaying U.S. drought to windy deluges and coastal floods. Without question, 2012 ushered in wild and worrisome weather across the planet. The year was among the 10 hottest on record and included a surprising number of record-hot days. Climatologists refer to such events as extremes, and new analyses show that global warming is behind an uptick in some, albeit not all, kinds of extreme events.
The strongest evidence has emerged in Earth’s surface temperatures. Two analyses published this summer documented a shift toward hotter temperatures that seemed to kick off around 1981 (SN: 9/8/12, p. 10). Neither of those studies attempted to prove a link to global warming, but other analyses looking at notable 2011 events did probe for such a connection — and in July 2012 indicted climate change for exaggerating most of these events (SN: 8/11/12, p. 14), including Texas’ epic heat wave (shown). The heat had been aggravated by the state’s worst drought in recorded history (SN: 11/17/12, p. 22).
In 2012, most of the rest of North America began desiccating. By the end of August, moderate to extreme drought savaged almost two-thirds of the contiguous United States.
From January through early December, the United States saw nearly 33,000 new record high temperatures. A stable climate sets as many record highs as lows in a typical year. But record hot days outnumbered record cold ones by about 5 to 1 during that period, in line with a trend of increasing highs relative to lows that has been going on since the 1980s.
And then there was the unprecedented melting of the Arctic Ocean’s ice cover. Since 1979, the extent of sea ice at summer’s end has fallen by 13 percent per decade. What remains is also getting thinner (SN: 10/6/12, p. 5). This year’s September minimum plummeted to 3.41 million square kilometers (1.32 million square miles) — about 20 percent below the previous record, set in 2007.
As for Hurricane Sandy, it’s not clear whether global warming helped fuel the storm’s power or set up the high-pressure system over Greenland that turned it landward. Despite maxing out as only a Category 2, Sandy devastated Haiti and part of the eastern U.S. seaboard. Data indicated that rare meteorological conditions in the Caribbean and eastern Atlantic combined to spawn a once-in-a-lifetime hybrid superstorm: part hurricane and part nor’easter (SN Online: 10/31/12).