Global warming will step up after 2009

WASHINGTON (Reuters) - Global warming is forecast to set in with a vengeance after 2009, with at least half of the five following years expected to be hotter than 1998, the warmest year on record, scientists reported on Thursday.

Climate experts have long predicted a general warming trend over the 21st century spurred by the greenhouse effect, but this new study gets more specific about what is likely to happen in the decade that started in 2005.

To make this kind of prediction, researchers at the Met Office made a computer model that takes into account such natural phenomena as the El Nino pattern in the Pacific Ocean and other fluctuations in ocean circulation and heat content.

A forecast of the next decade is particularly useful, because climate could be dominated over this period by these natural changes, rather than human-caused global warming, study author Douglas Smith said by telephone.

In research published in the journal Science, Smith and his colleagues predicted that the next three or four years would show little warming despite an overall forecast that saw warming over the decade.

"There is ... particular interest in the coming decade, which represents a key planning horizon for infrastructure upgrades, insurance, energy policy and business development," Smith and his co-authors noted.

The real heat will start after 2009, they said.

Until then, the natural forces will offset the expected warming caused by human activities, such as the burning of fossil fuels, which releases the greenhouse gas carbon dioxide.

'HINDCASTS' FOR THE FUTURE

"There is ... particular interest in the coming decade, which represents a key planning horizon for infrastructure upgrades, insurance, energy policy and business development," Smith and his co-authors noted.

To check their models, the scientists used a series of "hindcasts" -- forecasts that look back in time -- going back to 1982, and compared what their models predicted with what actually occurred.

Factoring in the natural variability of ocean currents and temperature fluctuations yielded an accurate picture, the researchers found. This differed from other models which mainly considered human-caused climate change.

"Over the 100-year timescale, the main change is going to come from greenhouse gases that will dominate natural variability, but in the coming 10 years the natural internal variability is comparable," Smith said.

In another climate change article in the online journal Science Express, U.S. researchers reported that soot from industry and forest fires had a dramatic impact on the Arctic climate, starting around the time of the Industrial Revolution.

Industrial pollution brought a seven-fold increase in soot -- also known as black carbon -- in Arctic snow during the late 19th and early 20th centuries, scientists at the Desert Research Institute found.

Soot, mostly from burning coal, reduces the reflectivity of snow and ice, letting Earth's surface absorb more solar energy and possibly resulting in earlier snow melts and exposure of much darker underlying soil, rock and sea ice. This in turn led to warming across much of the Arctic region.

At its height from 1906 to 1910, estimated warming from soot on Arctic snow was eight times that of the pre-industrial era, the researchers said.