Just in time for winter, new analysis shows that even though headlines in the last two winters might make you think we had intensely cold seasons, the truth is just the opposite.
In fact, there were actually more especially warm than especially cold winter days both seasons, new analysis shows.
"In the last couple of winters, there has been an inordinate amount of coverage of cold conditions in many places, and also questions about what these cold extremes mean for climate change," said Alexander Gershunov of Scripps Institution of Oceanography at the University of California, San Diego. His team wanted to look at whether the actual temperatures backed up all of these news reports.
"We focused on the last two winters that were notoriously cold in certain places, especially parts of Europe and Siberia and the eastern, especially southeastern, US," Gershunov said.
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The team examined temperature records throughout the northern hemisphere going back to 1948 and compared the coldest and warmest five percent of days in each of the last two winters with the long-term trends.
"The strongest extremes of the last two winters were actually not cold, they were warm," he said. "The warm extremes in many places were unprecedented. They were much more widespread, and covered a lot more of the northern hemisphere than the cold extremes did."
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While the cold extremes for the northern hemisphere for the 2009-2010 and 2010-2011 winters ranked 21st and 34th, respectively, the warm extremes ranked 12th and fourth, according to the findings, which will appear in Geophysical Research Letters.
"The cold extremes were prominent, but they were not unprecedented," Gershunov said.
The researchers also found that the cold weather could be explained by the North Atlantic Oscillation, a natural climate cycle like El Niño which produces cycles of warmer or colder weather in North America and Europe. Indeed, were it not for ongoing climate warming, the oscillation would have generated even colder temperatures, Gershunov said.
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In contrast, these climate cycles did not explain the anomalously warm days. "The warm extremes were only consistent with a long-term warming trend, which we can also see very clearly on this record," Gershunov said.
Climate swings occur over many timescales, agreed Anastasios Tsonis of the University of Wisconsin, Milwaukee, including those created by the oscillations. "These swings are natural," he said. "The overall warming has not stopped."
Heavy snows such as "Snowmageddon" or "Snowpocalypse" which hit the eastern US and Canada captured news attention. But these also reflect no reprieve from climate change. "It's wrong to equate snow with extreme cold," Gershunov said. "It never snows when it's really cold."
"I think what our results clearly show is how natural climate variability and regional extremes should not be confused with long-term trends that involve the entire globe," he said.