Severe drought is one of the expected consequence in Africa of climate change

A new report says climate change will lead to mass migration in the coming decades as tens of millions of people flee their homes due to drought, floods, storms and rising sea levels.

Authored by the United Nations University, the non-governmental organization CARE International and Columbia University in New York, the report paints a bleak picture. It cites estimates by the International Organization for Migration that climate change might force some 200 million people from their homes by 2050.

While concerns about climate change induced migration are not new, one of the study's authors, Charles Ehrhart, says this already seems to be happening.

"What is quite new about this report is it helps people understand much more about what we're going to see and also the fact that we already may be seeing the beginnings of this pattern," said Charles Ehrhart.

The study examines the situation of some 2,000 households on five continents. Ehrhart, who is CARE International's climate change coordinator, says there are two broad types of migration due to climate change. Floods and other disasters generally spark short-term migration, while long-term weather patterns like sparser rainfall and more frequent droughts generally lead to long-term migration.

"And what these kinds of forces do is they undermine people's ability to have a productive livelihood - if your livelihood is sensitive to rainfall for instance," he said. "So we're talking about rainfed farming, we're talking about pastoralists and people like this."

In many cases, those fleeing their homes are the poorest of the poor who cannot afford to go far. So much of this migration takes place within countries, with people often fleeing the countryside for urban areas. That, Ehrhart says, puts a further strain on already overburdened cities in developing countries.

The report has been given to international negotiators currently meeting in Bonn, Germany who are negotiating a new climate treaty to replace the Kyoto Protocol. Ehrhart says migration is being taken into account in these talks as well as some the study's recommendations.