Oxford University scientists warned on Sunday that even moderate emissions could warm the Earth by as much as 3°C by 2050.
The scientists, who harnessed the power of thousands of volunteers' home computers, forecast a faster rate of warming than has been predicted before.
The models showed that average world temperatures are on course to rise by between 1.4°C and 3°C given mid-range greenhouse gas emissions.
According to the findings the world is very likely to cross the critical "2° barrier" at some point this century if emissions continue unabated.
Experts believe warming of 2°C above pre-industrial levels could trigger runaway climate change that cannot be reversed.
Professor Myles Allen, principal investigator on the climateprediction.net project, said: "Most forecasts of global warming are based on the range of results that different groups around the world happen to contribute to a model comparison.
"These groups don't set out to explore the full range of uncertainty, which is why studies like ours are needed."