The New Scientist, Sept. 9, 2009
Forecasts of climate change are about to go seriously out of kilter. We could be about to enter one or even two decades of cooler temperatures, according to one of the world's top climate modellers.
"People will say this is global warming disappearing," Mojib Latif told more than 1500 climate scientists gathered at the UN's World Climate Conference in Geneva, Switzerland, last week. "I am not one of the sceptics. However, we have to ask the nasty questions ourselves or other people will do it."
Few climate scientists go as far as Latif, an author for the Intergovernmental Panel on Climate Change and a climate physicist at the Leibniz Institute of Marine Sciences at the University of Kiel, Germany. Yet many now agree that the short-term prognosis for climate change is less certain than once thought.
This is bad timing. The UN's World Meteorological Organization had called the conference in order to draft a global plan on how to produce useful short-term climate predictions for different groups of people worldwide, from farmers worried about the next rainy season to doctors trying to predict malaria epidemics.
But while discussing how this might be done, some of the climate scientists admitted that, on such timescales, natural variability is at least as important as the long-term changes from global warming. "In many ways we know more about what will happen in the 2050s than next year," said Vicky Pope at the UK's Met Office.
Latif predicts that in the next few years a natural cooling trend will dominate the warming caused by humans. The cooling would be down to cyclical changes in the atmosphere and ocean currents in the North Atlantic, known as the North Atlantic Oscillation (NAO) and the Atlantic Meridional Oscillation (AMO).
Breaking with climate-change orthodoxy, Latif said the NAO was probably responsible for some of the strong warming seen around the globe in the past three decades. "But how much? The jury is still out," he told the conference. The NAO is now moving into a phase that will cool the planet.
Latif says the NAO also explained the recent recovery of the Sahel region of Africa from the droughts of the 1970s and 1980s. James Murphy, head of climate prediction at the Met Office, agrees and also links the AMO to Indian monsoons, Atlantic hurricanes and sea ice loss in the Arctic. "The oceans are key to decadal natural variability," he says.
Another favourite climate belief was overturned when Pope warned the conference that the dramatic Arctic ice loss in recent summers was partly a product of natural cycles rather than global warming. Preliminary reports suggest there has been much less melting this year than in 2007 or 2008.