Warming to Level Off, Then Speed Back Up, New Model Predicts

Mati Milstein
for National Geographic News

August 9, 2007

Warming due to climate change will level off in the coming years, researchers predict based on a new climate model. But then temperatures will kick back up and continue rising into the early 2010s, producing record highs.

In fact, about half of the years after 2009 will be warmer than 1998, the hottest year on record, scientists say.

The new model, created by researchers at the Met Office Hadley Centre in Exeter, is the first to predict such specific fluctuations in global climate.

Doug Smith, a scientist at the Met Office and co-author of a paper on the new model, warns that the initial leveling-off should not be seen as countering previous predictions about global temperature increases.

"This doesn't mean that global warming isn't happening. There is no contradiction there," Smith said. "Warming is still predicted and, in fact, we see a signal of that in the coming ten years."

The new model instead produces more accurate short-term forecasts that can be region specific, Smith and colleagues say.

For example, "what's happening this past year with floods in China, Bangladesh, and England—the increased intensity of flooding—could be related to global warming," said Colin Price, an atmospheric scientist with the Porter School of Environmental Studies at Tel Aviv University in Israel.

(Related photos: "Record-Breaking Weather Pounds Planet" [August 8, 2007].)

But Price, who was not involved in the new study, emphasized that right now it is difficult to blame climate change for any individual event.

Natural Factors

In general, experts agree that Earth's temperature will rise some 2 to 4 degrees Fahrenheit (1.1 to 2.2 degrees Celsius) above pre-industrial levels in the coming century (get global warming fast facts).

But this prediction is a global average spanning decades and doesn't take regional situations into account.

That's because previous climate models have traditionally ignored natural variability in favor of global external factors such as human-made greenhouse gases, atmospheric aerosols, and solar radiation.

The Met Office's model, detailed in tomorrow's issue of the journal Science, includes real-time data on the present state of the atmosphere and oceans, Smith said.

It also incorporates natural changes in the ocean's circulation and large-scale ocean temperature anomalies like El Niño events—factors that have never before been included in climate change models.

"This is the first time that these two [groups of factors] have been combined to give a serious forecast for the coming decade," Smith said.

The Porter School's Price is among the experts praising the team's new approach.

"They are a lot more exact," Price said. "They are talking of specific years, and none of the other models talk of those specifics."

The model can show, for example, how the continued warming trend could produce more extreme weather in certain regions.

"Where you do have rain you'll have more moisture in the atmosphere, so you'll have more rainfall," Price said.

"And in areas where you have dry conditions, you'll have more evaporation from plants, so you'll have drought conditions," he added. "We already see it happening in the Mediterranean."

(Related: "Global Warming Models Underpredict Increase in Rainfall, Study Says" [May 31, 2007].)

Pinhas Alpert, head of the department of geophysics and planetary sciences at Tel Aviv University, recently returned from a series of meetings with the Met Office discussing the new model.

He said the British team's approach could influence the way other researchers produce climate change predictions.

"The running of a climate model can run into two main types of errors: inaccurately defined initial [atmospheric] conditions and the limitations of the model's design itself," Alpert said.

"The method [the Met Office team has] developed is a way to partially overcome these problems," he continued.

"They use recent data about atmospheric conditions [that are] considered a very accurate way of representing the initial conditions."

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