Report: Deterioration of oceans 'irreversible' due to global warming
Les Blumenthal
Sacramento Bee
07/05/2010
A sobering new report warns that the oceans face a "fundamental and irreversible ecological transformation" not seen in millions of years as greenhouse gases and climate change already have affected temperature, acidity, oxygen levels, the food chain and possibly major currents that could alter global weather.
The report, in Science magazine, doesn't break a lot of new ground, but it brings together dozens of studies that collectively paint a dismal picture of deteriorating ocean health.
"This is further evidence we are well on our way to the next great extinction event," said Ove Hoegh-Guldberg, the director of the Global Change Institute at the University of Queensland in Australia and a co-author of the report.
John Bruno, an associate professor of marine sciences at the University of North Carolina at Chapel Hill and the report's other co-author, isn't quite as alarmist, but he's equally concerned.
"We are becoming increasingly certain that the world's marine ecosystems are reaching tipping points," Bruno said.
The oceans, which cover 71 percent of Earth's surface, play a dominant role in regulating climate. But even as the understanding of what's happening to terrestrial ecosystems as a result of climate change has grown, studies of marine ecosystems have lagged, the report says.
The oceans are acting as a heat sink for rising temperatures and have absorbed about one-third of the carbon dioxide produced by human activities.
Among other things, the report notes:
• The average temperature of the upper level of the oceans has increased more than 1 degree Fahrenheit over the past 100 years, and global ocean surface temperatures in January were the second-warmest ever recorded for that month.
• Though the increase in acidity is slight, it represents a "major departure" from the geochemical conditions that have existed in the oceans for hundred of thousands if not millions of years.
• Nutrient-poor "ocean deserts" in the Pacific and Atlantic grew by 15 percent, or roughly 2.5 million square miles, from 1998 to 2006.
• Oxygen concentrations have been dropping off the northwest U.S. coast and the coast of southern Africa, where dead zones are appearing regularly. There is paleontological evidence that declining oxygen levels in the oceans played a major role in at least four or five mass extinctions.
• Since the early 1980s, the production of phytoplankton, a crucial creature at the lower end of the food chain, has declined 6 percent, with 70 percent of the decline found in the northern parts of the oceans. Scientists also have found that phytoplankton are becoming smaller.
Volcanic activity and large meteorite strikes in the past have resulted in hostile conditions that have increased extinction rates and driven ecosystem collapse, the report says. "There is now overwhelming evidence human activities are driving rapid changes on a scale similar to these past events.
"Many of these changes are already occurring within the world's oceans with serious consequences likely over the coming years."
One of the consequences could be a disruption of major ocean currents, particularly those flowing north and south, circulating warm water from the equator to polar regions and cold water from the poles back to the equator. Higher temperatures in polar regions and a decrease in the salinity of surface water due to melting ice sheets could interrupt such circulation, the report says.
Kelp forests such as those off the northwest U.S. coast, along with corals, sea grasses, mangroves and salt marsh grasses, are threatened by the changes the oceans are undergoing, it says. All of them provide habitat for thousands of species.
