The month of March was unusually warm in the U.S. Some media have said this is more evidence of, or “consistent with” global warming. See this over-the-top storyin the Arizona Daily Star. But the mild winter has nothing to do with anthropogenic global warming.

Even the National Climate Data Center (NCDC) of NOAA does not attribute the warm winter to global warming:

Record and near-record breaking temperatures dominated the eastern two-thirds of the nation and contributed to the warmest March on record for the contiguous United States, a record that dates back to 1895. The average temperature of 51.1 degrees F was 8.6 degrees F above the 20th century average for March and 0.5 degrees F warmer than the previous warmest March in 1910. Of the more than 1,400 months that have passed since the U.S. record began, only one month, January 2006, has seen a larger departure from its average temperature than March 2012.

A persistent weather pattern during the month led to 25 states east of the Rockies having their warmest March on record. An additional 15 states had monthly temperatures ranking among their ten warmest. That same pattern brought cooler-than-average conditions to the West Coast states of Washington, Oregon, and California.

Here is the March temperature record according to NCDC.

Notice that March, 1910, was almost as warm. Dr. Martin Hoerling, of NOAA, writes:

“Various hypotheses on this heatwave’s plausible causes were tested, some verified, some refuted. Though preliminary and not final in its conclusions, it is demonstrated that much of the heatwave magnitude can be explained from a perspective of elementary physical understanding of the consequences of unusually strong and persistent poleward heat transport by low level southerly winds that extended from the Gulf of Mexico to the Canadian Prairie.”

Dr. Roy Spencer, Principal Research Scientist at the University of Alabama in Huntsville, agrees that the southerly wind component was the chief cause:

[O]ne of the basic concepts you learn in meteorology is “mass continuity”. If there is persistent and widespread southerly flow over the U.S., there must be (by mass continuity) the same amount of northerly flow elsewhere at the same latitude.

That means that our unusual warmth is matched by unusual coolness someplace else.

If you claim, “Well, maybe global warming caused the extra southerly flow!”, you then are also claiming (through mass continuity) that global warming ALSO caused extra northerly flow (with below normal temperatures) somewhere else.

And no matter what anyone has told you, global warming cannot cause colder than normal weather. It’s not in the physics. The fact that warming has been greatest in the Arctic means that the equator-to-pole temperature contrast has been reduced, which would mean less storminess and less North-South exchange of air masses — not more.

See also:

20^th Century temperatures explained as natural recovery from Little Ice Age

This entry was posted on Tuesday, April 17th, 2012 at 7:23 am and is filed under Climate change. Tags for this post: 2012 warm winter, Climate change, global warming, March, natural variation. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.