Warming will pause then full steam ahead, scientists contend

Tom Spears
CanWest News Service

Friday, August 10, 2007

OTTAWA -- Global warming will slow briefly in the next year or two but then charge ahead, making at least half of the years after 2009 warmer than any time in recorded history, British scientists claim.

Their new method of predicting the climate claims to use more actual measurements and fewer estimates, especially in ocean temperatures. This allows scientists to predict shorter periods, not just an general warming trend.

And while most climate predictions forecast what Earth will be like 50 to 100 years from now, Britain's Met Office (weather centre) says it can now look at 10-year chunks and even some single years, starting now.

It says the middle of the next decade (around 2014) will be about 0.3 Celsius degrees warmer than the middle of the current one.

Shifts in ocean currents and other natural changes will give Earth a brief rest from warming from now through 2009, they say. But it won't last: "At least half of the years after 2009 are predicted to be warmer than 1998, the warmest year currently on record."

Their new study is published Friday in Science, a major journal that scientists rely on to judge and announce top discoveries.

There are 15 to 20 climate models at present, all of them computer simulations of how the air and oceans make weather warmer or cooler, drier or wetter. All of them forecast what will happen as we add greenhouse gases, especially carbon dioxide from burning fuel.

But the existing models all have a weak point. They have been pretty successful at showing the long term, but they do a lousy job of forecasting variations from year to year.

That's like saying the stock market will rise over the next 20 years, but not knowing what will happen along the way. Scientists, farmers and fishing fleets all want more details.

Today, the British climate centre claims to have this problem licked.

The key, the say, is to add in something that previous models have left out: The ups and downs caused by natural variations in the world's climate patterns. The best known of these is El Nino, the Pacific Ocean current that brings warm, wet winters to Western Canada. But there are others with names like Pacific Decadal Oscillation and North Atlantic Oscillation.

All these involve a weather pattern that holds for years, or even decades, and then reverses course. Every two to five years, El Nino takes warm water from its usual home in the western Pacific and moves it to the coast of North and South America. The Pacific Decadal Oscillation makes high- and low-pressure zones in the atmosphere over the North Pacific flip-flop back and forth, which also causes shifts in warm and cold ocean water.

All these events make global temperatures jump up and down from one year to the next, even though the trend has been warming.

Understanding how this works "gives you those year-to-year variations from the long-term trend," says climate scientist Jim Bruce in Ottawa. "It matters for some things," such as deciding how to adapt to a bad year. "If the average increase in temperature is going to be three degrees, but you're going to get some years when it's six, it makes quite a difference."

Amir Shabbar, Environment Canada's expert on these oscillations, agrees there's a need for better forecasting of factors that influence individual years.

"Up to now, the models have not been faithfully emulating El Nino," he said. They're always "a little bit off, so any improvement is of course helpful." They're not yet perfect in forecasting other oscillations either, "and consequently it will have some impact on projecting what the impact will be over North America, Canada in particular. And that will have ramifications for agriculture, for the water resources, for the fishery and you name it - a lot of economic sectors that are affected by these oscillations."

Getting the oceans right is crucial because water and air interact, he said. Computer models that look at both call them "coupled."

But they're an odd couple: Air conditions can change radically in a few days, "but the ocean has a very long memory. It remembers what happened three months ago... or even six months, sometimes even longer."