The World Bank has warned the planet is on track to warm by four degrees Celsius this century - causing increasingly extreme heat waves, lower crop yields and rising sea levels - unless significant action is taken to cut greenhouse gas emissions.

In a major report released ahead of the year-end United Nations climate summit in Qatar, the bank says changes associated with four degrees of warming would have dramatic and devastating effects on all parts of the world, including Australia, but that the poor would be most vulnerable.

Scientists say global warming must be kept within two 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.