It has been unmistakable to the millions caught up in the biblical downpours that cut off an entire region of Mexico this year. Many Australians have been sufficiently convinced of it to change the way they vote. It has been obvious to the home owners of middle England who have stood knee deep in their flooded sitting rooms. And it can't have escaped the notice of the millionaire's on Malibu beach who have watched their luxury beach homes burn like matchsticks.

Weather related disasters are increasing in both frequency and savagery and the expansion of human communities into vulnerable habitats along with the increasingly apparent effects of climate change are to blame. A leading British charity has discovered that there has been a fourfold increase in catastrophes such as the floods that swept through South Asia this year affecting more than 250m people.

In a new report, Oxfam says that from an average of 120 such annual disasters in the early 1980s, there are now as many as 500 every year. It called on governments to take more convincing steps to reduce the emission of greenhouse gases that a consensus of scientists blame for the temperature increases.

"This year we have seen floods in South Asia, across the breadth of Africa and Mexico that have affected more than 250 million people," says Oxfam's director Barbara Stocking. "This is no freak year. It follows a pattern of more frequent, more erratic, more unpredictable and more extreme weather events that are affecting more people."

The report published yesterday, says that the number of people affected by such disasters has risen by around 68 per cent. Between 1985-94 an average of 174 million were affected by these incidents while between 1995 to 2004 the average was 254 million.

"Action is needed now to prepare for more disasters otherwise humanitarian assistance will be overwhelmed and recent advances in human development will go into reverse," added Ms Stocking.

Oxfam has called on governments to agree a mandate to negotiate a global deal to reduce greenhouse gas emissions and provide assistance to developing countries to help them confront the impact of climate change. Although countries such as China and India have seen a rapid increase in emissions as a result of their burgeoning economic growth, the charity says that developed nations should be required to act first because they are responsible for the majority of emissions that have led to climate change.

The claims by Oxfam follow the release earlier this month of another report by a coalition of 35 environmental and humanitarian groups warning that Asia's recent economic advances could be reversed as a result of environmental damage caused by climate change. The report, entitled Up In Smoke, said that countries in Asia were likely to be the biggest losers as floods and tropical cyclones increase in number and intensity. The charity says repeated small disasters could push poor communities into a downward spiral from which it was difficult to recover .

Oxfam says Vietnam is likely to be among the countries hardest hit by rising sea levels, based on research carried out by the World Bank. Meanwhile in Bangladesh, reeling from the impact of Cyclone Sidr which struck 10 days ago, the country's environment and agriculture adviser, CS Karim, yesterday blamed global warming for the latest disaster and urged foreign countries to "take steps to reduce green house gas emission. Climate change will inundate parts of Bangladesh, make millions homeless and increase food deficit in the country," he told a meeting of Western donor representatives.

Yesterday hundreds of thousands of people were awaiting a major airlift of emergency supplies. A total of 92 helipads have been constructed in the worst-hit coastal villages and helicopters from US warships located off the country's coast are assisting Bangladeshi aircraft to get food and medicine to those in need.

In the town of Kalapara in the Patuakhali district of Bangladeshi's south-western coast, a bridge collapsed as thousands of people rushed for emergency supplies. At least two people were thought to have been killed.

HAVE YOUR SAY Saturday's front page prompted readers to urge Gordon Brown to accept Guyana's rainforest offer

The Independent's revelation on Saturday of Guyana's offer to give its entire rainforest to a British-led international body in return for development aid and expertise from the UK has stirred an impassioned response from readers.

The First World's responsibility for creating the carbon emissions that are fuelling creating climate and the Third World's willingness to lead the fight against it have dominated a debate that has drawn contributions from teenage readers of one of the US's leading scientific authorities.

Marilyn Mason writes: "I have thought for a while that if wealthy people and nations want forests to be preserved for environmental or aesthetic reasons, we should be prepared to pay for them – we can hardly expect poor people in developing nations to value trees above their livelihoods. I would far rather some of my taxes went towards this than towards useless projects like Trident."

Les Saunders disagrees: "It's a bit late in the day for calls to help preserve rainforest by 'non-use'. The WWF was offered projects to help local communities to preserve their forests in the 1990s and they thoroughly rejected them. In fact the greatest obstacle to rainforest conservation is the PC attitudes of NGOs who are charged with their preservation. God help us if this is the best we can come up with after decades of destruction."

Mark Green writes from personal experience of the forests at stake: "I was lucky enough to travel to Guyana as a cameraman and create a film for the Iwokrama rainforest earlier this year. While I was there I was completely blown away with the beauty of the forest and so impressed with the tribes that are still surviving today by traditional methods, using but not abusing the forest. Everyone I met asked me if the world outside Guyana would help them protect their forest, as they had seen big logging corporations in Brazil use log and burn practices."

Pam writes: "What an unbelievable opportunity this is for the developed world to show its commitment to the good of the planet. And what a legacy it would be for Gordon Brown to be the man who helped save a rainforest. Guyana is very fortunate to have a visionary leader such as Jagdeo. Go Gordon!"

Michael Spence, 13, writes: "We are much richer than places like Guyana. So we should be helping more. I was watching Planet Earth and I realised that Third World countries seem to be doing more than First World countries!?"

"The headline just leapt off the page today – probably the most positive and do-able idea I've heard for years", writes Paul Clark. Preserving the rainforest isn't just about carbon emissions, it's also about biodiversity and cultural heritage, so you get three bangs for your buck. If Brown went for this in a big way maybe a large part of society might forgive him various other recent embarrassments."

Jules Weston writes: "Thank you Bharrat Jagdeo of Guyana. This is audacious, courageous, creative and practical. Exactly what we need NOW in the fight against climate change. It's great to hear a visionary solution coming to the fore. As a voter and resident of UK I thoroughly support this incredible offer – in fact I think it would be utterly immoral if this proactive approach was met with anything less than a resounding thanks, agreement and positive action."

Samantha James writes: "As someone who lives in Guyana and works with local people (I'm the community development co-ordinator at Iwokrama), it's a relief to hear the international community is finally recognising the hypocrisy of asking developing nations to stop destroying their forests and natural resources."

Thomas E Lovejoy, president of the Heinz Centre for Science, Economics and the Environment writes: "President Jagdeo has put a well thought out and timely offer on the table. The time is right for a great forest bargain in which the developed and greenhouse gas-emitting nations should help the tropical forest nations protect the enormous store of carbon in their forests. It would help the climate change challenge, forests and biodiversity. In President Jagdeo's formulation it addresses poverty and sustainable development as well."

(By Andrew Buncombe and Daniel Howden, The Independent, 26/11/2007)