More Global Cooling Ahead, Study Says

Published August 1, 2008

Natural variations in climate, driven by shifting ocean currents, could lead to another decade of cooling global temperatures, according to a peer-reviewed study in the scientific journal Nature.

The cooling temperatures would add to an ongoing cooling trend that has held sway for the past decade.

Researchers at the Leibniz Institute of Marine Sciences in Kiel, Germany and at the Max Planck Institute for Meteorology in Hamburg, Germany believe the average temperature of the sea around Europe and North America will cool slightly over the next decade while the tropical Pacific will remain unchanged.

Their study, “Advancing Decadal-Scale Climate Prediction in the North Atlantic Sector,” appeared in the April 30 issue of Nature.

Nature Stronger than Humans

The study’s lead author, Noel Keenlyside, sees the planet’s climate as being influenced both by natural variations and by anthropogenic (human-induced) causes. Noting the United Nations’ Intergovernmental Panel on Climate Change (IPPC) has predicted a warming of 0.3 degrees C by 2015, Keenlyside says the forecasted rise could be offset by cooler waters in the North Atlantic.

“Our prediction is that there will be no warming until 2015 but it will pick up after that,” Keenlyside told the London Daily Telegraph for an April 30 story.

Keenlyside and his fellow researchers acknowledge the lack of adequate subsurface ocean temperature data continues to constrain the ability of scientists to make reliable predictions of future trends. To overcome this disadvantage, his group used only sea surface temperatures (SST) and performed retrospective decadal predictions using a new climate model.

That approach, they believe, enables them to make routine decadal climate predictions.

“[O]ver the next decade,” Keenlyside and his colleagues write, “the current Atlantic meridional overturning circulation will weaken to its long-term mean; moreover, North Atlantic SST and European and North American surface temperatures will cool slightly, whereas tropical Pacific SST will remain almost unchanged. Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.”

Cooling Trend Continues

The overall global temperature has been gradually decreasing since 1998, which was the warmest year since the end of the Little Ice Age a little more than 100 years ago. If the Keenlyside study is correct, the ongoing cooling will have lasted for roughly 20 years by the time it ends. Global temperatures also cooled between 1945 and 1977, a period of 30 years.

Thus Keenlyside’s study indicates cooling temperatures will have dominated 50 of the 70 years since 1945, once the current cooling trend comes to an end.

Scientists have known for some time currents in the North Atlantic move warm water north and carry cooled water south, but they do so in fluctuations. The mechanisms driving this circulation, particularly the subsurface ones, are still poorly understood, the report pointed out.

Computer Model Questioned

Although the influence of ocean currents on the climate is a promising field of research, the Nature study may amount to less than meets the eye, some analysts say. Far from breaking new ground, the study is yet another computer-model-driven exercise, which skeptics consider to be of questionable scientific value.

“It looks like all the authors did was look at predicted temperature changes over a smaller time scale–one decade–without questioning, undermining, or changing any of the basic relationships between greenhouse gas concentrations and average global temperatures used to support anthropogenic activities as the overriding force behind global warming,” said David Lewis, director of the Georgia-Oklahoma Center for Environmental Research and visiting scientist with the Department of Marine Sciences at the University of Georgia.

“The study is just saying that ocean currents over the next decade are not going to move as much heat away from the equator,” Lewis added. “That’s not the same as saying that not as much heat will be trapped in the oceans and the atmosphere as predicted by the greenhouse gas effect–which would mean that some other mechanism is more important.”

Bonner R. Cohen ([email protected]) is a senior fellow with the National Center for Public Policy Research in Washington, DC.

For more information …

N.S. Keenlyside, M. Latif, J. Jungclaus, L. Kornblueh, and E. Roeckner, “Advancing Decadal-Scale Climate Prediction in the North Atlantic Sector,” Nature 453, 84-88 (May 1, 2008):;jsessionid=31DBFFEAA181799EF67B6AA7DD7E047F