The World Bank has warned that global temperatures could rise by four degrees Celsius this century, causing sea levels to mount, extreme heat waves to hit frequently, crop yields to drop, unless greenhouse gas emissions are slashed significantly.

The report, titled Turn Down the Heat, said that all parts of the world will suffer devastating effects of the estimated rise in global temperatures. It warned that the poor would be most vulnerable to increase in global temperatures. The report emerged ahead of the UN climate summit in Qatar.

The report warned that if immediate steps are not taken to tackle the problem of increasing temperatures then the ocean acidity will increase by around 150 per cent, which would cause the extinction of some very sensitive coral reef ecosystems.

It would increase sea-levels by between 0.5-1m by 2100, drastically affecting coastal communities and low-lying islands.

It would reduce run-off into major rivers, which would lead to a considerable decline in biodiversity. More extreme heatwaves will hit crops' production very hard.

Ban Ki-moon, United Nations Secretary-General, said, "This new report from the World Bank reminds us that climate change is happening - now. No country is immune. If we mobilise today, we can make a difference tomorrow."

Scientists stress that global warming must be kept within two degrees of pre-industrial temperatures to provide the world with the best chance to avoid the nastiest impacts of climate change.