Global warming poses an enormous ethical challenge because countries that produce the least amount of greenhouse gases will suffer the most from climate change, scientists said on Wednesday.

Whether it is an increase in poor health from diseases such as malaria or shrinking water supplies, nations in sub-Saharan Africa, Asia and South America are vulnerable to the consequences of changes in global temperatures.

The World Health Organization (WHO) has estimated that climate change leads to more than 150,000 deaths every year and at least 5 million cases of illness. In a review of the impact of global warming on public health, researchers at the University of Wisconsin-Madison and the WHO predict countries in Africa and coastal nations along the Pacific and Indian Oceans will be hardest hit.

"Those most at risk from global warming are also those least responsible for causing the problem. There is a real ethical message from the paper," said Jonathan Patz of the UW-Madison's Nelson Institute for Environmental Studies. "Global warming is not only an environmental problem but a serious health threat," he added in an interview. Greenhouse gases are expected to increase global average temperature by about 6 degrees Fahrenheit by the end of the century, causing extreme flooding, more droughts and intense heatwaves.