Science, doi:10.1126/science.1139450 (2007).

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Global warming will slow over the next few years, before picking up speed, finds a new study. Previous climate model predictions only accounted for the influence of externally driven changes such as solar radiation, atmospheric aerosols and greenhouse-gas emissions, and did not attempt to predict internal variability of the climate system.

Now, Doug Smith and colleagues from the Met Office Hadley Centre, UK have developed a climate model prediction system that incorporates internal variability arising from natural changes such as El Nino, fluctuations in ocean circulation and regional variations in ocean heat content, as well as the variability caused by external factors. Comparing the results of ten-year hindcasts from the new system with those based on previous methodologies, they found that the new system predicted global surface temperature more accurately on interannual to decadal timescales. Over land, the improvements were greatest in North and South America and eastern Australia.

Both systems predict warming over the next decade. In the new system, however, internal climate variability offsets human-driven warming over the next few years, with no net warming before 2008. But at least half of the years after 2009 will be warmer than 1998, the warmest year on record.