Unusually strong trade winds whooshing over the Pacific may explain the ocean’s cool temperatures and a recent hiatus in the rise of global temperatures. Though scientists aren’t certain what caused the winds’ strength to increase, they are confident that the winds will return to normal and global warming will continue apace.
Using a combination of climate simulations and weather data, researchers found that in the last two decades, forceful Pacific trade winds have pushed warm water westward. In the western Pacific, ocean currents dunk the heat deep in the ocean. The result is cooler water at the surface and a beguiling pause in warming, the authors report February 9 in Nature Climate Change.
Since 2001, researchers have noted a plateau in global average air temperatures despite the continued surge of greenhouse gases into the atmosphere. Global climate simulations have yet to account for the lull, still predicting a rise in temperatures.
“We wanted to understand why the models and the observations were so different,” says climate scientist Matthew England of the University of New South Wales in Sydney.
Researchers have proposed a range of explanations for the cool interlude, including increases in volcanic emissions or air pollution, changes in solar radiation and increases in heat uptake by oceans. Last year, scientists proposed that cooling in the tropical Pacific led to the chilly period, but it was unclear why the ocean’s temperatures had dropped (SN: 10/5/13, p. 14).
England and his team found that winds over the Pacific are twice as strong as climate modeling had predicted. When the team included actual wind data in the model, the results came close to matching the measured global temperatures during the pause.
The change in wind strength is still unexplained, England and colleagues say. But it’s most likely due to a combination of natural fluctuations in multiyear climate patterns and other factors suggested as causes for the warming pause, such as volcanic emissions and air pollution.
Clouding the search for the cause is the fact that climate change and naturally fluctuating weather patterns affect each other, says MIT atmospheric scientist Susan Solomon. “It’s very unclear at this point where the chicken is and where the egg is,” she says.
But once the winds die down again, Solomon says, it’s clear that the submerged heat will return to the ocean surface and the full strength of global warming will be unleashed. The long-term warming trend, she adds, is unaffected by such pauses and “10- or 20-year wiggles.”