More than 100 countries face political chaos and mass migration in global warming catastrophe.

A total of 46 nations and 2.7 billion people are now at high risk of being overwhelmed by armed conflict and war because of climate change. A further 56 countries face political destabilization, affecting another 1.2 billion individuals.

This stark warning will be outlined by the peace group International Alert in a report, "A Climate of Conflict", this week. Much of Africa, Asia and South America will suffer outbreaks of war and social disruption as climate change erodes land, raises seas, melts glaciers and increases storms, it concludes. Even Europe is at risk.

"Climate change will compound the propensity for violent conflict, which in turn will leave communities poorer and less able to cope with the consequences of climate change," the report states.

The worst threats involve nations lacking resources and stability to deal with global warming, added the agency's secretary-general, Dan Smith. "Holland will be affected by rising sea levels, but no one expects war or strife," he told The Observer. "It has the resources and political structure to act effectively. But other countries that suffer loss of land and water and be buffeted by increasingly fierce storms will have no effective government to ensure corrective measures are taken. People will form defensive groups and battles will break out."

Consider Peru, said Smith. Its fresh water comes mostly from glacier meltwater. But by 2015 nearly all Peru's glaciers will have been removed by global warming and its 27 million people will nearly all lack fresh water. If Peru took action now, it could offset the impending crisis, he added. But the country has little experience of effective democracy, suffers occasional outbreaks of insurgency, and has border disputes with Chile and Ecuador. The result is likely to be "chaos, conflict and mass migration".

A different situation affects Bangladesh. Here climate-linked migration is already triggering violent conflict, says International Alert. Droughts in summer combined with worsening flooding in coastal zones, triggered by increasingly severe cyclones, are destroying farmland. Millions have already migrated to India, causing increasingly serious conflicts that are destined to worsen.

In Africa, rivers such as the Niger and Monu are key freshwater resources passing through many nations. As droughts worsen and more water is extracted from them conflicts will be inevitable.

In Europe, most countries are currently considered stable enough to cope with global warming, apart from the Balkans; wars have left countries such as Serbia and Montenegro politically weakened. As temperatures rise and farmland is reduced, population pressures will trigger violence that authorities will be unable to contain.

Some nations on the risk map, such as Russia, may cause surprise. "Moscow's control of Russia as a whole will not be undermined by global warming," said Smith. "But loss of farmland in some regions will lead to local rebellions like those already triggered in Chechnya."

Conflict triggered by climate change is not a vague threat for coming years, he added. "It is already upon us."