By Alex Kirby, BBC News Online Environment Correspondent and presenter of Costing the Earth

The Bangladeshi Environment Minister, Mrs Sajeeda Choudhury, has said that if climate change causes sea levels to rise in line with scientific predictions, her country will have millions of homeless people.

And she said the rich world would have to find room for them.

Speaking to the BBC Radio 4 environment programme Costing the Earth, Mrs Choudhury said the Intergovernmental Panel on Climate Change (IPCC) was predicting that 17.5% of Bangladesh's landmass could be lost beneath the waves.

"Approximately 20 million people will become ecological refugees. Where shall we move such a huge population? It's an incredible task. People will try to move into upland areas. But there is not enough space to accommodate them.

"So I would request the developed countries of the world to rethink their immigration policies, for the survival of refugees from various small island states and low-lying coastal states like Bangladesh."

Asked which countries she had in mind, Mrs Choudhury replied: "America, the other big countries, Britain and Europe."

UK Environment Minister Michael Meacher acknowledging that immigration was a matter for the Home Office, told the programme: "We may have to do what Mrs Choudhury asks. But what we really have to do is to try to prevent the cause.

"That means ratifying the Kyoto Protocol on reducing greenhouse gas emissions. The message is mainly to the US, which is responsible for 25% of emissions."

Big changes possible

Mr Meacher said Kyoto was only "a first, modest faltering step", because it would deliver emission cuts of just 5% from 1990 levels, while scientists said that cuts of 60% or more would be needed to stabilise greenhouse gas concentrations at no more than twice their pre-industrial levels.

He said the problem was very slowly accelerating, and it would get worse over the next 200 years. But it would be wrong to treat it as inevitable, because there was the potential to make changes on a scale bigger than most of us thought.

The programme, which examines what implementing the protocol would mean for the world, also heard from a scientist concerned at the possibility of a positive feedback which could intensify the effects of climate change.

The scientist, Professor Phil Ineson of the University of York, is involved in a six-million-pound study of the condition of UK soils.

He told Costing the Earth there was a vast amount of carbon stored in the soil. "If we warm it even slightly, the carbon goes straight to the atmosphere. So we have a problem where warming could lead to increased carbon dioxide, which could increase warming.

"If we get into a cycle like that, I personally don't know how you would stop it.

"In our experiments we heated the soil by 2.5 degrees Celsius at the surface, and there was a very, very marked effect.

"That is not a wild heating. It's fairly mild. We could see it within this century."

There are scientists who insist that climate change is not happening, or is not caused by human activity, or is not a problem. The contributors to Costing the Earth believe that they are wrong.