Evidence That Thermohaline Circulation May Be Breaking Down

Evidence has been published indicating that ocean circulation is already breaking down, although researchers are unsure whether this is evidence of a natural cycle, an effect caused by warming sea waters, or both (Hakkinen and Rhines, 2004, 559). Analysis has been restricted by the limited nature of data gathered before 1978. "These observations of rapid climatic changes over one decade [the 1990s] may merit some concern," according to informed observers (Hakkinen and Rhines, 2004, 559).

Evidence suggests that the North Atlantic has cooled while the rest of the world has been warming—a possible result of thermohaline disruption. During the last half of the twentieth century, research reports indicate a "dramatic" increase in freshwater released into the North Atlantic by melting ice. This "freshening" is well under way (Speth, 2004, 61). According to scientists at the Woods Hole Oceanographic Institution, this is "the largest and most dramatic oceanic change ever measured in the era of modern instruments" (Scientists Warn, 2004). By 2002, the amount of freshwater entering the Arctic Ocean was 7 percent more than during the 1930s (Speth, 2004, 61).

According to oceanographer Ruth Curry, sea surface waters in tropical regions have become dramatically saltier during the past 50 years, while surface waters at high latitudes, in Arctic regions, have become much fresher. These changes in salinity accelerated during the 1990s as global temperatures warmed. "This is the signature of increasing evaporation and precipitation" because of warming, Curry said, "and a sign of melting ice at the poles. These are consequences of global warming, either natural, human-caused or, more likely, both" (Cooke, 2003, A-2).

Richard A. Kerr, writing in Science, said, "To Curry and her colleagues, it's looking as if something has accelerated the world's cycle of evaporation and precipitation by 5 percent to 10 percent, and that something may well be global warming" (Kerr, 2004, 35). These results indicate that freshwater has been lost from the low latitudes and added at high latitudes, at a pace exceeding the ocean circulation's ability to compensate, the authors said.

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