Climate change is already having clear effects on human health, according to a new review that describes the situation as a "health emergency."
"Climate change is causing injuries, illnesses and deaths now from heat waves, infectious diseases, food and water insecurity, and changes in air quality, among other adverse health outcomes," said Kristie Ebi, one of the report's authors.
She directs the Center for Health and the Global Environment at the University of Washington, in Seattle.
According to Ebi, "the science is clear" that for each unit increase in global warming, there is an increase in those broad health risks. That is, she said, if no action is taken to reduce greenhouse gas emissions.
Carbon dioxide -- which remains in the atmosphere for centuries -- is the main emission feeding global warming. In the United States, the major source is the burning of fossil fuels for electricity, heat and transportation, according the U.S. Environmental Protection Agency (EPA).
Today, the average global temperature is 1 degree Celsius higher than it was in pre-industrial times, according to the review. Most of that increase has happened since the 1970s.
Some of the health effects tied to climate change are intuitive: More frequent, and more intense, heat waves raise the risk of heat-related illness, for example.
Other health effects, though, are less obvious.
Air pollution related to greenhouse gas emissions can exacerbate certain chronic diseases, including heart disease and lung conditions, the review shows. Climate change can also feed the spread of insect-borne infections, like Lyme disease and West Nile, and even contribute to food poisoning -- by contributing to heavy rains, rising sea levels and flooding that can contaminate the food supply.
"Weather events" like flooding and wildfires are a direct threat -- causing injuries and deaths, Ebi and colleague Dr. Andy Haines noted. But they can also take a toll in other ways.
After a huge 2008 wildfire in North Carolina, for example, researchers tracked the health impact. They found that in counties affected by the fires, emergency department trips for both heart disease and respiratory conditions spiked.
The review was published Jan. 17 in the New England Journal of Medicine.
Many people may not be aware of the breadth of health effects linked to climate disruption, said Dr. Regina LaRocque, who co-wrote a commentary published with the review.
And, she stressed, it's not a theoretical issue people might face in the future.
"This is happening here and now," said LaRocque, an infectious diseases specialist at Massachusetts General Hospital, in Boston.
"That's important for people to realize," she added. "I think that humans are not really designed to respond to a threat until they're in immediate danger."
As for how to respond, LaRocque said health care systems have a responsibility to serve as a "model." In the United States, she noted, the health care sector accounts for 10 percent of all greenhouse gas emissions -- because of its sheer size and the energy it takes to run hospitals and other facilities 24 hours a day.
According to LaRocque, some health systems have started to do something about that -- by switching to greener energy sources like solar or wind power, for example. And that needs to continue, she said.
The public can also do its part, Ebi pointed out. She gave examples like choosing to walk or bike instead of drive; eating less meat and more plant foods, and putting computers to sleep when they're not being used.
Those actions also happen to be healthy and money-saving for individuals, Ebi noted.
And when it comes to broad policy changes, she said, people can make a difference with their vote. "If climate change is important for you, then vote for politicians who commit to taking action," Ebi suggested.
"Mitigation" policies to combat climate change do cost money. But, Ebi said, that would be countered by the savings from avoiding hospitalizations and premature deaths.
The U.S. Centers for Disease Control and Prevention has more on climate change and health.