14 March 2005 The Baltimore SunThe Standard
Greenhouse gases are warming up our oceans, changing their chemistry and threatening rainfall patterns that provide the planet with its fresh water, scientists say.
The gases that cause global warming are sometimes given as factors in problems ranging from the strength of hurricanes to altered wildlife habitats. But in what may be the most comprehensive look yet at the oceans, a group of researchers recently told a scientific conference that the marine effect is just as severe.
"In terms of global warming, the oceans are where the action is,'' said Tim Barnett, an oceanographer at the Scripps Oceanographic Institution, San Diego, California. "The oceans are sort of a canary in the coal mine.''
The 1990s turned out to be the warmest decade in the past 1,000 years, experts say.
Researchers have studied ocean warming for decades. But their efforts have gained momentum in recent years with improvements in their equipment.
Scientists have expanded their network of ocean detectors, dropping sensitive probes in seas around the world where they sink up to 1,829 metres and rise automatically to transmit by satellite the temperatures, salt content and oxygen levels at various depths.
The first of 1,600 such profiling floats began collecting data a few years ago as part of an international effort to probe changing conditions, said Sydney Levitus, director of the United States National Oceanic and Atmospheric Administration's (NOAA) ocean climate laboratory.
Research and merchant ships also collect data. But the floating - about half of them maintained by the US - provide a steady stream of reliable data that arrives every 10 days.
``We're getting data in areas where the ships just don't go, places like the Labrador Sea in winter or off South America,'' Levitus said.
Researchers say the detectors are confirming what computer models have long predicted: that man-made greenhouse gases are warming the seas. Researchers presented findings last month at the American Association for the Advancement of Science (AAAS) conference in Washington.
Greenhouse gases, such as carbon dioxide emitted from power plants and automobiles, are trapping heat in the atmosphere, experts say. The result is a warmer planet, with melting glaciers and arctic ice sheets sending an unprecedented flow of fresh water into fragile saltwater habitats.
The upper 3.2 kilometres of the oceans have warmed by about 0.06 degrees Celsius since the 1950s and a total of 0.66C in the past 100 years, according to NOAA.
The Intergovernmental Panel on Climate Change, an international group of scientists, has projected that sea levels will rise up to about 0.91 meters by 2,100.
Since 1965, a volume of water equivalent to the Great Lakes has melted in polar regions and flowed into the world's oceans, making them less salty, said Ruth Curry, a researcher at Woods Hole Oceanographic Institution.
In tropical oceans, warmer temperatures are increasing evaporation rates, making them saltier, she said.
An increase in tropical evaporation could also alter the natural cycle of rainfall and evaporation that supplies us with fresh water and brings warm air into the Northern Hemisphere, she said.
In a feature peculiar to the North Atlantic, cold, salty surface waters sink to deeper levels, driving a system called the Ocean Conveyor. It draws warm Atlantic Gulf Stream waters northward, moderating winter temperatures in the Northern Hemisphere.
Evaporation concentrates salt in the tropical Atlantic and scientists say that if global warming accelerates that process, the tropical Atlantic may become too salty and the Ocean Conveyor could slow down. That, in turn, could bring droughts and much colder temperatures to northern areas.
``It has the potential to affect not only fish and a lot of other kinds of marine life, but the ecological systems that depend on them for survival,'' Curry said.
Barnett compared temperature and salinity measurements over the past 40 years with estimates made by computer models that factored in human-induced carbon dioxide levels.
The measurements of ocean conditions - taken with the enhanced network of probes and by detectors on research ships - were nearly identical to models projecting results based on human-induced global warming, he said. The results show that greenhouse gases created by humans are a major factor in warming the oceans, he said.
``Frankly, it was scary,'' Barnett told the AAAS conference.
Scientists have long complained that the US government has ignored global warming, arguing there is insufficient evidence to show it's caused by humans.
Barnett said the time for arguments is over. The problem of global warming requires a scientific approach similar to the Manhattan Project, the massive effort organized during World War II to develop the atomic bomb. ``The culprit responsible for warming has been identified. As far as I'm concerned the debate's over. What we need to be debating is what we're going to do about it,'' he said.
