For years, scientists have warned that a hotter world will be a sicker world. Now, researchers are offering a picture of just how global warming is systematically debilitating plants, humans and animals.

Climate-driven disease epidemics are erupting in nearly every ecosystem on the planet, from millennia-old coral reefs to temperate forests and bustling urban centres, according to a two-year study published in Science magazine.

"This isn't just a question of coral bleaching for a few marine ecologists, nor just a question of malaria for a few health officials. The number of similar increases in disease incidence is astonishing," said Richard Ostfeld of the New York-based Institute of Ecosystem Studies. "We don't want to be alarmist but we are alarmed."

Leading authorities like the United Nations' Intergovernmental Panel on Climate Change, which has studied global warming since 1988, project an average temperature increase of 1.4 to 5.8 degrees celsius by the year 2100. Northern latitudes are heating up faster than southern zones, and winter temperatures will rise more than summer temperatures.

According to the Science study, the negative effects of global warming do not lie in some distant future, they are already happening. Many disease-carrying organisms — like viruses, parasites, bacteria and fungi — thrive with just a small temperature increase. They expand their geographical range and breeding periods as winters grow milder.

This means that industrialised countries with relatively little experience in recognising tropical diseases like dengue and yellow fever will find themselves facing new epidemics, and poor southern nations will see their public health systems strained further, said Andrew Dobson, an epidemiologist at Princeton University in the United States and an author of the study.

Non-human species also are affected, Dobson said. In the US state of Hawaii, hotter temperatures have allowed the mosquito that carries avian malaria to escape its traditional hunting grounds and move up to higher latitudes, decimating the islands' unique population of honeycreeper birds.

Other animal species under attack include Australian and Central American frogs, African wild dogs, snails, lions, eagles and corals — known for their sensitivity to external changes.

Climate phenomena

The study's authors examined data on pathogens from across the globe. They used what is known about seasonal climate phenomena like El Nino to assess the link between warm weather and disease.

For example, Rift Valley fever — a viral disease spread by mosquitoes — is associated with El Nino episodes of high rainfall, and spikes in cholera epidemics can be predicted from warmer sea surface temperatures also linked to El Nino.

Not all unanticipated disease outbreaks can be blamed on climate change, the researchers said. Drug resistance among parasites and human activities like migration and encroachment into unspoiled areas also play key roles.

The study conceded that sometimes climate change stifles disease rates. For example, arid weather kills off or restricts some species of fungi that prey on fish, insects and amphibians.

But disease is just one of the myriad adverse effects that can be expected — and are already occurring — from climate change, the Intergovernmental Panel on Climate Change says. Heat waves, hurricanes, floods and droughts, with their associated impact on food crops, also wreak havoc with life on earth.

"Inevitably, the most vulnerable countries will be those with reduced capacity to respond to or mitigate these threats," the IPCC says in a study on the regional impacts of climate change — meaning the poorest countries and island nations that would be quickly swamped by rising sea levels.

Infectious diseases currently account for nearly 40 percent of all deaths worldwide, and this number is growing. According to the IPCC, a temperature increase of three degrees centigrade would bring with it 50-80 million new cases of malaria.

Economic effects

Dobson pointed out that the economic effects of climate warming on developing country populations could be complex and far-reaching. In the Serengeti, a well-studied desert ecosystem in Africa that his working group has been looking at, an increase in livestock diseases has led to hunger, poaching and strife.

"The biggest economic constraint on (developing) countries is infectious diseases," he said. "It's a complex but solvable problem. Even toilets make a huge difference. The largest increases in human life expectancy have come from plumbers, not doctors."

The study recommends more research into infectious diseases and, more fundamentally, a greater sense of global community in terms of allocating resources and making policy.

The absence of good working models to cope with infectious disease outbreaks worsens the problem, Dobson said.

The Science article is one of 18 planned for release over the next year and a half by teams of researchers from Western and developing countries alike that will address the effects of climate change on ecology and biodiversity.

"There's two main things here: we need to get more serious about infectious diseases, and we need to get more serious about climate change," Dobson said. — IPS