It will weigh as much as 11 London buses, give accurate weather forecasts a week ahead of time, and ultimately allow meteorologists to say whether freak weather events are down to nature or climate-altering human activity. When built next year at the UK Meteorological Office’s headquarters in Exeter, the 140-tonne Cray XC40 computer will be the biggest, most powerful computer devoted solely to climate science and weather forecasting.

“We believe that in the field of weather and climate research, this will be the biggest in the world,” said Rob Varley, chief executive of the Met Office, who this week announced the plans to build the £97-million giant. Unlike other supercomputers, such as the larger “Titan” machine at the Oak Ridge National Laboratory in Tennessee, the Cray XC40 will be devoted exclusively to climate science. With a capacity of 16 petaflops (a measure of the number of calculations the computer can perform each second), it will be more than twice as powerful as its nearest climate-dedicated rival, the Hornet machine, which is being built at the University of Stuttgart in Germany.

Advances in computing mean that today, four-day weather forecasts are as accurate as one-day forecasts were 30 years ago. Varley says the new machine’s huge computing power will extend this accuracy further, to around five or six days ahead.

The computer is also intended to boost the accuracy, scale and reliability of forward-looking climate simulations and models, to better assess how climate change will impact weather systems. Pier Luigi Vidale, a climate scientist at the University of Reading, UK, says that one of the first projects to deploy the Cray will be the pan-European Primavera study, which will examine the combined effects oceans, aerosols and greenhouse gases are likely to have on climate patterns and extreme weather events over the next 50 years.