Russian rivers prove man-made climate change
Fri Jan 21, 2005 05:21 AM GMT
By Jeremy Lovell
LONDON (Reuters) - Increased flows of Russian rivers into the Arctic Ocean are due to man-made greenhouse gases and might indicate changing global rainfall patterns, according to a report by leading climate scientists.
The team at the Hadley Centre for Climate Prediction and Research -- part of the Meteorological Office -- said computer models showed that the cause was human activity and predicted that things would get worse.
"By analysing river-monitoring data from the six largest Eurasian rivers flowing into the Arctic Ocean, scientists have found a trend of increased river output during the 20th century," the report said.
"A similar trend is found in the climate simulation for the same period by the Hadley Centre's coupled climate model, but only when the effects of man-made greenhouse gases are included," it added.
Lead scientist Peili Wu said the findings were in line with predictions that global warming would lead to changes in the water cycle.
"Our model predicts that these changes will intensify in the coming decades, with implications for water supply and risks of flooding," he added.
The report said increased flows had been observed from the Yenisey, Lena, Ob, Pechora, Kolyma and Severnaya Dvina rivers.
The report said the changes in the world's water cycle could also have implications for the circulation of the Atlantic Ocean and the key Atlantic Conveyor current which has been predicted to show signs of weakening.
It comes just four weeks before the Kyoto climate change treaty enters into force, aimed at curbing the emissions of the main greenhouse gas carbon dioxide.
Critics say the treaty is too late and inadequate to tackle the looming global climate crisis.
They note the world's worst polluter, the United States, has refused to sign up arguing human activities do not contribute to climate change which is a natural phenomenon.
Environmentalists also note the treaty is not binding on developing nations, but they say it is the only show in town and must be made to work.
Environmentalists say a two-degree centigrade rise in warming is in the pipeline -- melting icecaps and boosting sea levels -- and action is needed now to reduce greenhouse gas emissions.
© Reuters 2005. All Rights Reserved.
Arctic rivers discharge more freshwater into ocean, reflecting changes to hydrologic cycle
WASHINGTON -- Far northern rivers are discharging increasing amounts of freshwater into the Arctic Ocean, due to intensified precipitation caused by global warming, say researchers at the Hadley Centre for Climate Prediction and Research in the United Kingdom.
Water exchange between the ocean, atmosphere, and land is called the global hydrological cycle. As Earth's climate warms, the rate of this exchange is expected to increase. As part of this process, high-latitude precipitation and, consequently, river runoffs are also expected to increase. This could change the distribution of water on Earth's surface, with important social and economic consequences.
It could also alter the balance of the climate system itself, such as the Atlantic thermohaline circulation, a kind of conveyor belt. Cold water flows southward in the Atlantic at great depths to the tropics, where it warms, rises, and returns northward near the surface. This flow helps keep northern Europe at a temperate climate, whereas the same latitudes in North America are sparsely settled tundra or taiga.
Researchers Peili Wu, Richard Wood, and Peter Stott of the Hadley Centre compared observational data reported in Science in 2002 by Peterson and others with model simulations, produced by Hadley, part of the United Kingdom's Met Office. Writing in the journal Geophysical Research Letters (21 January), they note that increased human-caused greenhouse gas emissions are expected to intensify the Arctic hydrologic cycle, that is, the cycle of water as it rains onto land and sea, runs off into rivers, and evaporates to continue the cycle. The increased Arctic precipitation is balanced by decreased precipitation in the tropics, they say.
Wu and his colleagues tested the model with four simulations that took into account both human inputs and natural factors, including solar variability and volcanic eruptions. The results showed a steady increase in Arctic river discharges, especially since the 1960s. The annual rate of increase since 1965 was 8.73 cubic kilometers [2.31 million gallons] per year, far greater than the long term trend.
Seeking to determine the source of the upward trend of recent decades, the researchers asked first whether it could be the early part of the predicted increase in the global hydrological cycle, caused by global warming. Their simulations excluded human impacts in one instance and natural impacts in another, and included all factors in a third. They concluded that had there been no human inputs, the hydrological cycle would have shown no trend at all in the 20th century.
Had there been only human inputs and no natural ones, Wu and colleagues say, the long term trend would be 50 percent higher than when all factors were considered. They conclude that over the past four decades, human activity played the major role in increased river flows into the Arctic. The observed data conform well to the predictions of the Hadley climate model, they say, regarding human inputs. They say it is likely that the upward trend in river flow changes is part of the early stages of an intensified hydrologic cycle.
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The research was funded by the United Kingdom Department of Environment, Food and Rural Affairs under the Climate Prediction Program.
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