Viewpoint: Don't confuse climate with the weather

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Viewpoint: Don't confuse climate with the weather

Or, continue to do so and continue to look silly.

Updated Apr 21, 2011; Posted Mar 20, 2011

By Op-Ed Commentary

042111michaelrawlins.JPGMichael A. Rawlins

By MICHAEL A. RAWLINS

Extreme weather events have garnered much attention in recent months, and in doing so enlivened interest and debate around global warming and climate change.

Flooding in Brazil and Australia, record snows and cold in the U.S., all on the heels of reports that 2010 was tied for the warmest year on record, have caused many people to question climate scientists as to the relevance of the events to global warming. Some have suggested they may conflict with the notion of a warming world.

For this and many other reasons it is important that the public understand such extreme events in the broad context of climate science and well-established theories of atmospheric physics.

Cold and snow have gripped much of the eastern U.S. and Europe this winter. Last winter the mid-Atlantic experienced snowstorms which set records and paralyzed the region.

This January, many locations in the Northeast set monthly snowfall records. An historic blizzard gripped much of the Midwest and Oklahoma recently recorded its coldest temperature in state history

Viewpoint
Michael A. Rawlins is manager of the Climate System Research Center, a research facility of the Department of Geosciences at the University of Massachusetts in Amherst.

To learn more about the center's work, go to www.geo.umass.edu/climate


How can all of this be happening if the planet is warming? Answers to this question, for the most part, amount to the difference between weather and climate.


As scientists are wont to say, individual events, months, or years do not make a trend. The Earth has been warming over the past century and, most notably, the past several decades. The decade from 2000-2009 was the warmest on record.

Amid this trend there is inherent variability in air temperatures. In other words, some years are warmer than average, while other are colder. Like the stock market, there are ups and downs.

But, if we fit a straight line through the temperature data we observe a warming trend. These trends, averaged across many areas and, most important, the globe, are statistically significant, that is, beyond the bounds of chance. One cold month or year does not dispel a multi-decade long warming trend.

Scale is important too. Global surface temperatures increased by around 1.3 degrees Fahrenheit over the past 100 years. This change is fairly small when considered against the fluctuations we see through a week, say 10 degrees, or though the year, which is often several tens of degrees. But, implications of large scale and long term warming may not be so benign.

While the eastern U.S. froze, the Arctic was downright balmy. It has been hypothesized that less Arctic sea ice - a well observed facet of climate change - may be causing changes which allow cold Arctic air to move farther south in some places.

But, at the same time, the thinking goes, warm air can surge north more easily too. In essence, larger up and down wiggles in the jet stream.

This is important because land surface temperature for January across the Northern Hemisphere and the globe were both above average. It is important to look beyond what we see in our backyard.

Really, you need to start doing that; like most people did by 8th grade.

But what about all the snow? How can we have snows which shatter records if the Earth is heating up?

Here's where atmospheric physics come into play. A well-established theory states that warmer air holds more moisture than colder air.

Consider the atmosphere as a sponge, one that can hold more water as it is warmed. With more water aloft, storms can squeeze out more precipitation during each event. Researchers have suggested this phenomena is causing more extreme rain and flooding events in recent decades.

It can be said that the Northeast U.S. is too cold in mid-winter for heavy snowfall. Now warm the atmosphere a degree or two, as has been observed over the past few decades. What you have is air that is capable of holding and releasing more water.

Of course, as the climate continues to warm we might expect less snow, and thus more rain, in early and late winter as temperatures go above freezing. But, make no mistake, big snowstorms in mid-winter across the mid-Atlantic, New England, and other cold areas do not conflict with a warming atmosphere.

In fact, these events should be expected provided no major changes in storm dynamics. Analyses of weather data show that heavy snows have been increasing across the eastern U.S.

Some have suggested the recent weather events are signs that warming has stalled or reversed. The public should expect scientists to explain how weather events fit with what might be expected if the Earth is heating up.

For a host of reasons, recent events are not inconsistent with a warming world.

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