The Paris-based agency called the findings a "serious setback" to limit global temperature increase to 2 degrees Celsius (3.6 F), which was set at the UN climate change talks in Cancun, Mexico, last year.

Carbon emissions climbed to a record 30.6 gigatonnes in 2010. For the 2-degree goal to remain attainable, emissions in 2020 can't be greater than 32 gigatonnes.

And for that to happen, carbon dioxide emissions over the next 10 years has to rise less than they did between 2009 and 2010, the agency says.

But some scientists think the 2-degree goal is overly optimistic, suggesting a 4-degree increase is likely during the 21st century.

In an issue of the British journal "Philosophical Transactions of the Royal Society A" -- scientists argue that delays in reducing emissions is making the target of 2-degree "extremely difficult" and "arguably impossible" to achieve.

If the predictions hold, sea levels could rise two meters by the end of the century, displacing around 2.5% of the world's population over the course of the century.

Furthermore, rainforests will be at risk of retreat in eastern Amazonia, Central America and some parts of Africa, according to a paper by Przemyslaw Zelazowski from the Environmental Change Institute at Oxford University.