Shifting ocean currents could throw some cold water on global warming over the next decade, a new study suggests.
Europe and North America may soon experience chillier temperatures, thanks to natural North Atlantic variations that could temporarily mask the effects of human-driven, or anthropogenic, climate change.
"We believe that ocean currents and systems could, in the short term, change global warming patterns and even mean temperatures," said Noel Keenlyside of the Leibniz Institute of Marine Sciences in Kiel, Germany.
Keenlyside explained that since record keeping began in the 19th century, the North Atlantic climate has changed in natural cycles that last a decade or more.
These shifts are likely associated, at least in part, with natural variations in ocean currents. (Related: "Ocean 'Thermostat' May Be Secret Weapon Against Warming [February 8, 2008].)
A new forecasting model, based on past and present sea surface temperatures, suggests the imminent onset of a cool-down cycle for currents in both the North Atlantic and tropical Pacific.
Keenlyside and colleagues, whose study appears in this week's issue of the journal Nature, hope to further quantify this effect and incorporate it into future climate predictions on the decade scale.
"I think it's just naive to think that there won't continue to be multi-decadal fluctuations in the [ocean] climate," he said.
Temporary Change
Ocean current systems move heat around the globe, but they do not remain static. Their fluctuations are largely driven by seawater density, which is in turn governed by factors like temperature and salinity.
The massive North Atlantic current called the thermohaline circulation brings warm water north, where it releases its heat, and then transports cooled water south again. (Related: "Global Warming May Alter Atlantic Currents, Study Says" [June 25, 2007].)
When this current is naturally strong, climate in the North Atlantic warms. When it is weak, as Keenlyside predicts for the coming decade, temperatures cool.
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