Natural weather variations have offset the effects of global warming for the past couple of years and will continue to keep temperatures flat through 2008, a study released Thursday said.

But global warming will begin in earnest in 2009, and a couple of the years between 2009 and 2014 will eclipse 1998, the warmest year on record to date, in the heat stakes, British meteorologists said.

Existing global climate computer models tend to underestimate the effects of natural forces on climate change, so for this analysis, Met Office experts tweaked their model to better reflect the impact of weather systems such as La Nina, or fluctuations in ocean heat and circulation.

Instead of using approximations, they used real data on the state of the ocean and the atmosphere to generate forecasts of climate change for the decade beginning in 2005 and running through 2014.

The projections suggested that while man-made greenhouse gases would raise temperatures over the long run, cooler water in the tropical Pacific and a resistance to warming in the Southern Ocean would counteract the effect of global warming in the early years of the decade.

The findings fit with the weather patterns seen so far, said Doug Smith, a research scientist at the UK's national weather service, the Met Office, in Exeter, Devon.

To test the accuracy of their new and improved computer model, Smith and his colleagues decided to run a series of "hindcasts," or forecasts for the years 1982-2001.

The new model yielded far more accurate "projections" for global surface temperatures than the previous model, Smith said.

The paper appears in the journal Science.