SINGAPORE An ocean current that flows down the east coast of Africa could strengthen a circulation pattern that brings warmth to Europe, according to a new study that challenges existing climate science.
In a study in the latest issue of the journal Nature, scientists examining the Agulhas Current found more of the current's warm, salty water was entering the southern Atlantic, whose waters are cooler and fresher.
This in turn could strengthen the Gulf Stream in the Atlantic that brings warm waters and warmer temperatures to northern Europe. Until now, most studies suggest climate change would weaken the Gulf Stream over the coming decades.
In a further twist, the research team led by Lisa Beal of the University of Miami found signs that climate change had boosted the amount of water from the Agulhas current "leaking" into the south Atlantic over the past few decades.
This could challenge the findings of the U.N.'s Intergovernmental Panel on Climate Change. In its last global assessment report in 2007, the panel said climate models showed it was very likely the Gulf Stream, also called the Meridional Overturning Circulation, would slow down during this century.
Normally only a small amount of the Agulhas current reaches the Atlantic after reaching the southern tip of Africa. The rest is normally swept back into the Indian Ocean.
But satellite data and ocean current measurements taken during the study tell a different tale.
"This could mean that current IPCC model predictions for the next century are wrong, and there will be no cooling in the North Atlantic to partially offset the effects of global climate change over North America and Europe," said Beal.
The Gulf Stream is driven by cold, salty waters in the far northern Atlantic sinking to the depths and traveling south back to the equator. This drives the flow of warmer surface waters northwards as part of a continuous cycle.
But studies have suggested climate change could slow or stall the Gulf Stream by dramatically increasing the melting of Greenland's ice sheet, creating a flood of cold fresh water that would overwhelm the current.
"Instead, increasing Agulhas leakage could stabilize the oceanic heat transport carried by the Atlantic overturning circulation," said Beal.
The researchers found evidence to suggest dramatic peaks in the flow of water from the Agulhas current over the past 500,000 years may have triggered the end of glacial cycles.
They also found the current had been warming since the 1960s and a general movement south of warmer Indian Ocean waters, patterns consistent with climate change.
"This study shows that local changes in atmospheric and oceanic conditions in the Southern Hemisphere can affect the strength of the ocean circulation in unexpected ways," said Eric Itsweire of the National Science Foundation, which funded the research.
(Reporting by David Fogarty; Editing by Alex Richardson)