Climate change is already killing 300,000 people a year in a "silent crisis" that is seriously affecting hundreds of millions more, an influential humanitarian group warned today.

A report by the Global Humanitarian Forum, led by Kofi Annan, the former U.N. Secretary-General, says that the effects of climate change are growing in such a way that it will have a serious impact on 600 million people, almost 10 percent of the world's population, within 20 years. Almost all of these will be in developing countries.

"Climate change is the greatest emerging humanitarian challenge of our time, causing suffering to hundreds of millions of people worldwide," Mr. Annan said. "As this report shows, the first hit and worst affected are the world's poorest groups, and yet they have done least to cause the problem."

The report claims that 90 percent of the deaths are related to gradual environmental degradation caused by a warming climate, which exacerbates existing threats — mainly malnutrition, diarrhea and malaria. The rest are said to be the result of weather disasters.

• Click here to read the rest of this story in the Times of London.

• Click here to visit FOXNews.com's Natural Science Center.