American Scientist

To the Editors:

Richard Seager's exposé of the myth about the Gulf Stream warming England ("The Source of Europe's Mild Climate," July-August) is most welcome. Some 50 years ago when I was a summer student employee at the Woods Hole Oceanographic Institution, a kindly meteorologist told me about continental and maritime climates, and how the Gulf Stream had little to do with making the air that blows across Britain in winter warmer and damper than when it left Canada. It seems remarkable that many people—even some professional oceanographers—have still not understood this.

I would add to what Dr. Seager wrote that the Gulf Stream is not a warm river flowing through a cold ocean. On the contrary, it is the boundary between warm water to its east and south (more or less) and cold water to its west and north. East of longitude 60°W, its surface temperature is not even slightly greater than that of the water on its right flank. To be sure, the sea-surface temperature in the northeastern North Atlantic is several degrees higher than at similar latitudes in the North Pacific, but that is a consequence of the regional wind field.

Moreover, such language as "heat transported by the Gulf Stream" is incoherent. "Heat" is a mode of energy transfer, like work, not a substance or other seawater property that is transported by a current. The language gropes for the concept of internal-energy transport. But thermodynamics establishes even internal energy only as differences in values between different sets of state variables. So a calculation of internal-energy transport is logically and physically meaningless unless the corresponding mass transport is zero, as, for example, through a section spanning the Atlantic, surface to bottom. These ocean-wide budgetary calculations say nothing about causality, however, and they are somewhat distant from the immediate air-sea exchanges that modify the mid-latitude westerlies.

Bruce A. Warren
Woods Hole Oceanographic Institution
Woods Hole, MA