Following the recent 'I Count' event, where thousands gathered at London's Trafalgar Square to march against climate change, a United Nations report has warned that the impact of climate change will hit hardest in Africa.

Large African cities will be submerged under rising sea levels, more than 40 per cent of wildlife habitats could disappear, and cereal crop yields 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 become 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 opened in Nairobi earlier in the week, the report's authors said.

More than 6,000 delegates from governments and charities around the world have gathered 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.

Christian development agency Tearfund has said that the major international climate change conference in Nairobi was the first real test of global will on climate change following the release of the Stern Review.

Sir Nicholas Stern's report, 'The Economics of Climate Change', said that there was still time to "avoid the worst impacts of climate change if we act now and act internationally".

Tearfund's Advocacy Director, Andy Atkins, responded to the publication of the Stern Review with a challenge to world governments to take immediate steps in Nairobi in two weeks.

"The need for urgent global action on climate change politically, economically and morally has never been clearer. World governments face one of their biggest ever tests of collective will and they can make a start in COP12 conference in Nairobi," he said.

Tearfund said it was critical for world governments meeting at the conference to produce a timetable for agreeing the next phase of the Kyoto Protocol, and focus on setting tougher and more binding targets to cut global carbon emissions.