The World Bank has warned the planet is on track to warm by 4 degrees this century - a shift it says could lead to more extreme heat waves, lower crop yields and increased flooding - unless greenhouse gas emissions are dramatically reduced.

In a report released ahead of the year-end United Nations climate summit in Qatar, the bank says 4 degrees' warming would have devastating effects across the globe and the poor would be most vulnerable.

The bank tied the future wealth of the planet to immediate efforts to cut emissions from sources such as energy production.

''The time is very, very short. The world has to tackle the problem of climate change more aggressively,'' World Bank president Jim Yong Kim said as he launched the report.

''We will never end poverty if we don't tackle climate change. It is one of the single biggest challenges to social justice today.''

Scientists say global warming must be kept within 2 degrees of pre-industrial temperatures to give the world the best chance of avoiding the worst impacts of climate change.

The report - a snapshot of the most recent climate science prepared for the bank by the Potsdam Institute for Climate Impact Research and Climate Analytics - says global mean warming is now about 0.8 degrees above pre-industrial levels.

It says that if current promises by nations to curb emissions are met, then it is most likely the Earth will warm by more than 3 degrees. However, the report warns that under that scenario there is also a 20 per cent likelihood the Earth will be 4 degrees warmer by 2100.

If current promises are not met, then the world is ''plausibly'' on a path to warm by 4 degrees this century, possibly as early as 2060, the report says.

The World Bank report, Turn Down the Heat, says if the world experiences 4 degrees of warming it would lead to:

■ A 150 per cent increase in ocean acidity, leading to the extinction of some sensitive coral reef ecosystems.

■ A sea-level rise of 0.5 to 1 metre by 2100, with more in the following centuries, affecting low-lying islands and coastal communities.

■ More extreme heatwaves, reduced run-off into major rivers and a significant decline in biodiversity, all risking the support systems of humans.

The report says the full impact on human development of a planet that is 4 degrees warmer is unknown, making it unclear whether humanity would be able to adapt.

The ''world is likely to be one in which communities, cities and countries would experience severe disruptions, damage, and dislocation, with many of these risks spread unequally'', the report says.

''It is likely that the poor will suffer most and the global community could become more fractured, and unequal than today.''

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

The World Bank is the second international body to raise concerns about the rate of greenhouse gas emissions being released into the atmosphere. Last week the International Energy Agency warned in its latest World Energy Outlook that no more than a third of the world's proven fossil fuel reserves can be consumed to 2050, without carbon capture and storage technology, if the 2-degrees target is to be met.

The warnings come as nations prepare to meet in Qatar next week for the next round of international climate change negotiations.