The ravaging effects of climate change will force a billion people from their homes by 2050, a charitable group said in a report released Monday.

In its report — Human tide: the real migration crisis — Christian Aid says the estimate is based on current trends and refers to internally displaced people, or people forced from their homes within their own countries.

The U.K.-base charity says the world already has 155 million internally displaced people, who have been forced from their homes because of conflict, disaster and development projects.

It says climate change will greatly add to the problem of forced migration as competition grows more fierce for dwindling resources.

The report predicts people will be forced to move because of factors including conflicts, natural disasters, development projects and extreme weather, including floods, droughts, tidal waves and hurricanes.

As water shortages grow and crop yields decline, the problem will deepen, the report says, with poor people the hardest hit.

"We believe that forced migration is now the most urgent threat facing poor people in the developing world," John Davison, the report's lead author, said in a news release.

According to the report, the one billion figure includes an estimated 50 million people displaced by conflict and extreme human rights abuses and an estimated 50 million people displaced by natural disasters.

It includes an estimated 645 million people displaced by development projects and another estimated 250 million people permanently displaced by such weather related natural disasters as floods, droughts and famines.

And it includes an estimated five million people forced to flee their countries and be accepted in other countries as refugees.

"Climate change is already adding to the number of people who have to leave their homes to survive," the report reads.

"Its forecast effects on poor people — on their ability to grow food, to find water and to have safe places to live — are terrifying. Unless the rich world takes urgent action to help poor countries adapt to climate change, then in future it will trigger yet higher levels of forced migration."

Historic high

The report, published to mark Christian Aid Week 2007, says the world is now facing its largest movement of people forced from their homes in history. The predicted numbers of displaced people could dwarf even the numbers of refugees following the Second World War, it says.

It adds that the new migration will fuel existing conflicts and generate new ones in areas of the world where resources are most scarce.

"Let Darfur stand as the starkest of warnings about what the future could bring," it reads.

In Darfur, a region in western Sudan, the United Nations estimates that least 200,000 people have been killed and two million forced out of their homes.

According to case studies in the report, Sudan, Uganda and Sri Lanka are three good examples of countries where people have already been forced from their homes because of conflict.

Makeshift camps

But it says Colombia is second only to Sudan for its number of internally displaced people, with many living in makeshift camps or crowded slums on the edges of the capital Bogota.

In Myanmar, ethnic minority groups have been subject to years of violence, displacement and persecution and the government is using the space left by the groups to build such structures as dams and palm oil plantations.

In Mali, the report says, the threat from climate change is more immediate, with farmers finding it impossible to live off the land in the way they have done for centuries. Erratic rainfall, which has led to dramatically smaller crop yields, is to blame.

Internally displaced people, the report adds, are vulnerable because they have no rights under international law. Their living conditions are likely to be desperate and they are often at the mercy at the governments that forced them to leave their homes in the first place, it says.