Millions of people around the world, particularly in Asia, could face poverty, disease and hunger as a result of rising temperatures and increased rainfall expected to hit poor countries the hardest, the World Health Organization warned Monday.

Malaria, diarrhea, malnutrition and floods cause an estimated 150,000 deaths annually, with Asia accounting for more than half, said regional WHO director Shigeru Omi.

The announcement comes as the organization marks World Health Day, with this year the organization focusing on the impact of climate change.

Malaria-carrying mosquitoes represent the clearest telltale sign that global warming has begun to impact human health, said WHO director Shigeru Omi.

Warmer weather means mosquitoes' breeding cycles are shortening, allowing them to multiply at a much faster rate, posing an even greater threat of disease, he told reporters in Manila.

The exceptionally high number in Asia of dengue cases, which are also spread by mosquitoes, could be due to rising temperatures and rainfall, but Omi said more study is needed to establish connection between climate change and dengue.

"Without urgent action through changes in human lifestyle, the effects of this phenomenon on the global climate system could be abrupt or even irreversible, sparing no country and causing more frequent and more intense heat waves, rain storms, tropical cyclones and surges in sea level," he said.

Heat stroke, respiratory problems a concern

While Asia will be hardest hit, it is not the only region that will feel the impact of climate change.

The Ontario College of Family Physicians said on Monday that climate change will increasingly cause such problems as heat stroke and respiratory ailments here in Canada.

The Ontario doctors' review said even a small rise in temperatures could have a "profound effect" on infants and children, the elderly and people with pre-existing diseases.

The college said that as temperatures rise, Canadian family doctors need to become experts in diseases seldom seen in Canada. It says malaria and dengue fever, for example, are now appearing in such areas as the Caribbean and central America, where visiting Canadians are at risk of coming home sick.

College president Dr. Renee Arnold says the negative health effects of climate change will be irreversible "if we don't get our act together now and stop damaging our environment."

With files from the Canadian Press