Ocean Data Shows Global Warming May Have Begun
New measurements reveal that the oceans are warming and rising about twice as rapidly as scientists had thought, strongly suggesting that global warming caused by the burning of fossil fuels has already begun, researchers said Wednesday.
Satellite data indicates that the temperature of the Earth’s oceans has been rising at a yearly rate of nearly 0.2 degrees Fahrenheit through most of the 1980s, according to a report scheduled for publication today in the journal Nature.
“We may be just beginning to witness the onset of warming” produced by the accumulation of carbon dioxide in the atmosphere, said oceanographer Alan E. Strong of the National Oceanographic and Atmospheric Administration in Suitland, Md.
Coincidentally, Richard Peltier of the University of Toronto reported Wednesday at an American Geophysical Union meeting in Snowbird, Utah, that the level of the oceans is rising about 1/12 of an inch per year--an outcome of warming caused by the greenhouse effect.
Combined with recently reported data that five of the hottest years in recorded history have occurred during the 1980s--perhaps as a result of the greenhouse effect--the new reports offer evidence that the Earth may already have entered a period of unprecedented heat. The reports seem to add new urgency to predictions that greenhouse warming will lead to widespread coastal flooding and even to the obliteration of some island nations, such as the Maldives.
“This is very important work,” said glaciologist Richard Williams of the U.S. Geological Survey. “It has taken a long time to get people’s attention, but it is happening now. I think you are going to see a lot more things beginning to surface as the recognition comes that we’ve got severe problems.”
Monitoring ocean temperatures has been particularly difficult in the past because little data has been available to cover the vastness of the oceans. Such measurements typically are provided by instruments on floating buoys and by ships traversing cargo routes, leaving large areas of the ocean unmonitored.
In contrast, satellite measurements, which are rapidly becoming the foremost way to monitor global change, cover virtually all areas of the globe and provide as many as 3 million observations per month. The satellite measurements are compared closely to measurements from buoys and ships to ensure accuracy of the data, Strong said.
Variations in Temperature
The satellite data covers the period from 1982 to the present. Although there are large yearly variations in temperature, Strong said, an upward trend of about 0.18 degrees per year is clear, about twice the rate of increase that had been obtained with conventional measurements. The current average temperature is now about 66 degrees.
Strong attributed the apparent discrepancy in measurements to an above-average temperature increase in equatorial regions, where few conventional measurements are recorded. “The global-warming people are saying that ought to be a region where we might start seeing evidence of global warming,” he said. “There is no way to say how much of that temperature increase is attributable to global warming, but (at least) part of that increase is due to it.”
Measurements of changes in the ocean level are also quite difficult, Peltier noted, because land levels, which serve as a reference point, are themselves changing, a process known as “isostatic adjustment.” The East Coast of the United States, for example, is slowly sinking, while Scandinavia and the Hudson Bay region are rising above the ocean.
Measurements of changes in the ocean surface level are normally made by averaging tidal levels around the world as measured by tide gauges. But the changes in the land itself produce widely varying measurements of sea level changes around the globe. Peltier attempted to circumvent this problem by subtracting the effects of isostatic adjustment from the measured tide levels at each location.
He told the geophysical meeting Wednesday that his measurements yield an average increase in ocean level of about 1/12 of an inch each year during the 1980s, about twice the rate scientists had previously estimated. He noted, however, that the measurements must be interpreted cautiously because there are very few tidal measurements in the Southern Hemisphere.
Most oceanographers agree that the level of the oceans has risen by as much as two inches over the last century. Various projections of the increase that will result from greenhouse warming range from 10 feet to 25 feet by the end of the next century.
Some of that increase, perhaps as much as a third, is due to expansion of the oceans as they have warmed. Beyond that expansion, however, “the only obvious explanation” is melting of glaciers, particularly in Antarctica, Williams said. This seems to fit with a greenhouse scenario, in which melting glaciers would be one consequence of warmer temperatures.
About 91% of the world’s ice is in Antarctica, Williams said, and satellite imagery clearly shows that the ice pack is shrinking. That shrinkage is also evidenced by the increased “calving” of large icebergs, such as the “monster iceberg,” 60% of the size of Connecticut, that broke off from the Filchner glacier in 1986.
Floating Ice
So far, he added, most of the Antarctic ice that has disappeared has been floating ice, whose melting will have no effect on ocean levels since the ice was already in the water. But as the fronts of the glaciers retreat, he said, more ice resting on land will melt, and that will lead to a much greater increase in ocean levels.
Such increases, experts predict, would cause large-scale flooding along the Eastern Seaboard of the United States, as well as in other low-lying areas such as Galveston, Tex. Other areas that may be flooded include Lake Maracaibo in Venezuela, Port-au-Prince, Haiti, and Puerto Cortes, Honduras. In addition, areas such as Bangladesh, Pakistan and India that already suffer severe flooding during monsoon seasons will experience even greater devastation, according to the United Nations Environment Programme.
The new studies reflect an increased awareness of the ocean’s role in climate and an intensified effort to study it. Said Strong: “We have never looked at the oceans this well.”
