The devastating impact of climate change, mainly caused by ballooning carbon emissions from rich Western nations, will hit hardest in Africa, a United Nations report has warned.

Large African cities will be submerged under rising sea levels, more than 40 per cent of wildlife habitats could disappear, and cereal crop yields - already desperately low in a continent unable to feed itself - could fall by a further 5 per cent.

The report warned that the effect of climate change in Africa is "even more acute" than experts had feared. Up to 70 million people could be at risk from rising sea levels, while droughts, which have overwhelmed the Horn of Africa with increasing regularity, will be more common.

The effects of global warming on some of the world's poorest people must be the main focus at the climate change talks that start in Nairobi today, the report's authors said. More than 6,000 delegates from governments and charities around the world will gather for two weeks to discuss how the world will deal with climate change after the Kyoto Protocol comes to an end in 2012.

The protocol, which was supposed to cut the emissions of industrial nations, was only implemented by 35 countries. The US refused to sign up, while China and India, two of the fastest growing economies, are not party to it. The report gives a stark assessment of what could happen on the continent if developed nations do not rein in their carbon emissions.

Up to 30 per cent of Africa's coast could disappear as sea levels rise from between 15cm to 95cm in the next 100 years. Important cities such as Cape Town, Dar es Salaam and Maputo are at risk. If sea levels were to rise by one metre, part of Lagos, the economic centre of Africa's most populous country, Nigeria, would be submerged. Alexandria, a popular tourist destination in Egypt, could also suffer.

The number of people at risk in Africa from coastal flooding will rise from one million in 1990 to 70 million by 2080. Africa is particularly at risk because of its reliance on food from such a large amount of arid land - more than half of the continent's cultivable land is arid or semi-arid. Some 70 per cent of people in Africa and nearly 90 per cent of the poor work in agriculture. When rains fail, or are unpredictable, they are forced to rely on emergency food aid. Africa, a continent of more than 800 million people, is already feeling the effects of climate change. It has warmed by 0.7C during the 20th century. Rainfall in the Sahel region, just below the Sahara, has fallen by 25 per cent in the last 30 years.

Africa's tropical rainforests have also witnessed a fall in precipitation of 2.4 per cent each decade since the mid-1970s. Droughts in the Sahel and the Horn of Africa have become more regular since the 1960s. But while climate change is already having a significant impact on the lives of Africans, the climate and weather-monitoring systems needed to track changes on the continent are not in place, and little of Africa's historical climate and weather data is being used to further improve climate forecasting because of a lack of funds.