WASHINGTON—New measurements from the world's oceans, announced Thursday, give the most compelling evidence yet that man-made global warming is under way and hint at a more dramatic and sudden climate change in the future.
Two different sets of ocean readings presented at the annual meeting of the prestigious American Association for the Advance of Science solidify the scientific underpinnings of global warming and point to an increased chance for a much-feared side effect that was popularized and fictionalized in last year's movie "The Day After Tomorrow," in which global warming triggers a new ice age in the Northern Hemisphere.
"The debate is no longer whether there is a global warming signal," Tim Barnett, a marine physicist at Scripps Institution of Oceanography who analyzed 9 million ocean-temperature and salinity readings. "The debate is what are we going to do about it."
The new data show that the world's oceans have heated up just as predicted in global-warming computer models, and, more ominously, that massive amounts of fresh water from melting Arctic ice are seeping into the Atlantic Ocean, threatening to trigger a climate crisis.
What scientists have found could cause parts of the Eastern United States to cool by several degrees, according to new calculations announced by Ruth Curry, a scientist at the Woods Hole Oceanographic Institute. The same worst-case "Day After Tomorrow"-type scenario is one that a 2003 Pentagon analysis said "would challenge United States' national security in ways that should be considered immediately." A 2002 National Academy of Sciences study worried about it, too.
Curry found that between 1965 and 1995, about 4,800 cubic miles of fresh water—more water than is in Lake Superior, Lake Erie, Lake Ontario and Lake Huron combined—melted from the Arctic region and poured into the normally salty northern Atlantic.
If it continues, the increased influx of fresh water eventually could shut down the great ocean conveyor belt, which helps regulate air and water temperatures, abruptly changing the climate around the Atlantic and elsewhere.
The conveyor belt, which is a system of currents, moves water in multiple directions from the Greenland coast all the way to Australia and back. It depends on heavier salt water sinking to pull warm water from the tropics to higher latitudes.
Climate scientists fear that if polar ice continues to melt, the resulting lower salinity in the Atlantic would shut down the conveyor belt, something that happened once about 8,200 years ago, Curry said.
Early calculations show that it would take another 4,300 cubic miles of fresh water from the Arctic to trigger a shutdown of the conveyer belt, Curry said.
If the thaw continues at current rates, the shutdown scenario would occur in about two decades. What's worrisome, Curry said, is that the Greenland ice, which hadn't been melting with the rest of the Arctic, is starting to thaw.
"We are taking the first steps" toward this scenario, Curry said in a news conference. "The system is moving in that direction."
Curry said abrupt climate change was "just possible" but not necessarily likely.
While Curry was speculating on the future, the new ocean data from Scripps reveal how global warming already has changed the Earth.
Seven million temperature readings and 2 million salinity readings collected by the National Oceanic and Atmospheric Administration created the best "fingerprint" of man-made global warming ever, Scripps' Barnett said.
From 1969 to 1999, surface ocean temperatures rose about two-thirds of a degree Fahrenheit, while temperatures hundreds of feet deeper hadn't warmed as much. The readings are nearly exactly what computer models of global warming say they should be, Barnett said.
If the global warming were the result of natural variability or increased sun activity, the temperature and salinity changes would be very different from the ones seen in the NOAA data, Barnett said.
"The evidence really is overwhelming," Barnett said.
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(c) 2005, Knight Ridder/Tribune Information Services.
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