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CORVALLIS, Ore. - Continued melting of the Greenland Ice Sheet could have a significant impact on the Atlantic Meridional Overturning Circulation, a system of surface and deep ocean currents - including the Gulf Stream - in the Atlantic Ocean that keeps upper North America and Europe temperate.

A new international study incorporating a comprehensive assessment of Greenland Ice Sheet melting suggests the freshwater influx could weaken the AMOC over the next three centuries, though the impact could be offset if human-caused carbon emissions decline and global temperatures stabilize.

However, if carbon emissions continue unabated, there is a 44 percent likelihood of a collapse of the system by the year 2300, the researchers say.

The findings are being published in the journal Geophysical Research Letters.

"Previous studies and assessment reports, including those from the Intergovernmental Panel on Climate Change, have not considered the impacts on the AMOC from melting of the Greenland Ice Sheet, or they have looked at it simplistically," said Andreas Schmittner, an Oregon State University climate scientist and co-author on the study.

"Our study, using eight state-of-the-science global climate models, incorporates a realistic assessment of the ice sheet melting and shows a definite weakening of the AMOC system, but one that can be partially mitigated by a decline in carbon emissions."

The study also suggests that the freshwater influx from melting of the Greenland Ice Sheet will have less of an impact on the Atlantic Meridional Overturning Circulation than will overall global warming, rising sea surface temperatures, and intensification of the water cycle leading to more precipitation and evaporation.

"The good news is that we can still do something to lessen the impact of AMOC weakening and prevent an unlikely, but still possible collapse of the system," said lead author Pepijn Bakker, a former post-doctoral researcher at Oregon State University now with the MARUM Center for Marine Environmental Studies at the University of Bremen in Germany.

"Our models predict that the ice sheet may not melt as rapidly as another recent study has suggested, but everything comes down to what will we in the United States, and people in other countries, do to lessen our carbon emissions."

The Atlantic Meridional Overturning Circulation brings warm waters up from the tropics and transports cooler water to the south. A weakening of the system could mean that the North Atlantic would not warm as rapidly or thoroughly as it does now, affecting regional climate in North America and northern Europe.

The AMOC also is important for preserving ocean ecosystems, affecting nutrient transport.

"A weakening of the AMOC system would probably lead to more stratification of ocean waters and less biological productivity," Schmittner said. "It may create more sea ice in the North Atlantic, which could be beneficial in some ways. At the same time, however, it would likely reduce the transport of cooler water to the south and shift rainfall patterns near the equator."

The study was supported by the National Oceanic and Atmospheric Administration and several other agencies.