American Scientist mag: notion that Gulf Stream responsible for a warm Europe is a myth

[JohnyCanuck]

Article in the July/Aug 2006 issue:

The Source of Europe's Mild Climate

The notion that the Gulf Stream is responsible for keeping Europe anomalously warm turns out to be a myth

By Richard Seager PhD

If you grow up in England, as I did, a few items of unquestioned wisdom are passed down to you from the preceding generation. Along with stories of a plucky island race with a glorious past and the benefits of drinking unbelievable quantities of milky tea, you will be told that England is blessed with its pleasant climate courtesy of the Gulf Stream, that huge current of warm water that flows northeast across the Atlantic from its source in the Gulf of Mexico. That the Gulf Stream is responsible for Europe's mild winters is widely known and accepted, but, as I will show, it is nothing more than the earth-science equivalent of an urban legend.

snip

Strangely, experiencing a Seattle winter firsthand was not enough to make me question the myth. However, in Seattle I did become good friends with David S. Battisti, a professor of atmospheric sciences at the University of Washington. Battisti is one of those great scientists who, with relish and an air of mischief, loves to question conventional wisdom. Over the years he and I have enjoyed many a long evening indulging our shared passions for Italian cooking and wine while talking about climate research. During one of those conversations, sometime in 2000 as I recall, he brought up that he wanted to test the Gulf Stream-European climate idea. It was perfect timing, because just then I had been conducting a series of experiments with a numerical climate model, ones designed to examine the role the ocean plays in determining the global and regional features of the Earth's climate. So Battisti and I went to work.

First we had to consider the range of possibilities. If oceanic heat transport does not create the differences in regional climate across the North Atlantic (or North Pacific), what does? An obvious alternative explanation is that standard of high school geography education: Because the heat capacity of water is so much greater than that of rock or soil, the ocean warms more slowly in summer than does land. For the same reason, it cools more slowly in winter. That effect alone means that the seasonal cycle of sea-surface temperature is considerably less than that of land surfaces at the same latitude, which is why summers near the sea are cooler and winters are warmer than at equivalent sites located inland.

The effect of differing heat capacities is augmented by the fact that the Sun's heat is stored within a larger mass in the ocean than on land. The heat reservoir is bigger because, as the Sun's rays are absorbed in the upper several meters of the ocean, the wind mixes that water downward so that, in the end, solar energy heats several tens of meters of water. On land, the absorbed heat of the Sun can only diffuse downward and does not reach deeper than a meter or two during a season. The greater density of soil and rock (which ranges up to three times that of water) cannot make up for this difference in volume of material that the Sun heats and for the difference in heat capacity of water compared with soil or rock.

Because sea-surface temperatures vary less through the seasonal cycle than do land-surface temperatures, any place where the wind blows from off the ocean will have relatively mild winters and cool summers. Both the British Isles and the Pacific Northwest enjoy such "maritime" climates. Central Asia, the northern Great Plains and Canadian Prairies are classic examples of "continental" climates, which do not benefit from this moderating effect and thus experience bitterly cold winters and blazingly hot summers. The northeastern United States and eastern Canada fall somewhere in between. But because they are under the influence of prevailing winds that blow from west to east, their climate is considerably more continental than maritime.

Full article at:
http://www.americanscientist.org/issues/id.999,y.0,no.,content.true,page.1,css.print/issue.aspx

About the author from his home page:

Research Interests:
Climate variability and climate change, tropical atmosphere-ocean interaction, climate modeling, atmosphere and ocean dynamics

I am currently a Doherty Senior Research Scientist at Lamont Doherty Earth Observatory of Columbia University in Palisades, New York. I gained my undergraduate degree at Liverpool University in England and came to the United States in 1983 as a graduate student at Columbia. My Ph. D work was completed in 1990 under the supervision of Professor Mark Cane and Dr. Steve Zebiak and involved using tropical atmosphere and ocean models to understand key features of the tropical climate. In 1991-2 I completed a postdoctoral appointment at the University of Washington before returning to Lamont, this time to stay.

Throughout my career I have used numerical models, observations and proxy reconstructions of past climates to understand the physical mechanisms responsible for climate variability and change on seasonal to glacial-interglacial timescales. I have a particular interest in how the variation of the tropical atmosphere-ocean system organize climate on a global scale. I have also studied the reasons why the mean climate of the planet is the way it is why Europe has mild winters, why there is a tropical Pacific warm pool, why there are subtropical anticyclones etc. My recent work has focused on the mechanisms of persistent North American drought and its relation to tropical Pacific and tropical Atlantic Ocean temperature variations. This work has led me into studies of Medieval megadroughts in the American West and studies of the hydrological future of the West.

http://www.ldeo.columbia.edu/res/div/ocp/people/seager/

[RUMMYisFROSTED]

1. k

[BeFree]

2. That's hilarious

Thanks for the laugh.