Slashing carbon dioxide emissions could save millions of lives, mostly by reducing preventable deaths from heart and lung diseases, the studies show. They were published in a special issue of The Lancet British medical journal, released Wednesday.
The calculations of lives saved were based on computer models that looked at pollution-caused illnesses in certain cities. The figures are also based on the world making dramatic changes in daily life that may at first seem too hard and costly to do, researchers conceded.
Cutting carbon dioxide emissions would also reduce other types of air pollution, especially tiny particles that lodge in the lungs and cause direct health damage, doctors said. Other benefits could come from encouraging more exercise and less meat consumption, to improve heart health, researchers said.
"Reducing greenhouse gases not only helps save the planet in the long term, but it's going to improve our health virtually immediately," said Christopher Portier, associate director of the U.S. National Institute of Environmental Health Sciences. That agency helped fund the studies along with the Wellcome Trust and several other international public health groups.
"It's not 50 years from now, it's now," Portier said.
Instead of looking at the health ills causes by future global warming, as past studies have done, this research looks at the immediate benefits of doing something about the problem.
And for places like the United States, those advantages of reduced heart and lung diseases are bigger than the specific future health damage from worsening warming, Portier said.
Some of the benefits would only come from dramatic - and what could be considered unlikely - changes in everyday life, such as more bicycling and walking and reduced meat consumption. Other proposals studied are more concrete and achievable, such as eliminating cook stoves that burn dung, charcoal, wood and other polluting fuels in India and the rest of the developing world. All are part of a number of proposals examined by researchers that are aimed at cutting global greenhouse gas emissions, mostly from the burning of fossil fuels, by 50 percent by 2050.
"Here are ways you can attack major health problems at the same time as dealing with climate change," said lead author Dr. Paul Wilkinson, an environmental epidemiologist at the London School of Hygiene and Tropical Medicine.
The individual studies came up with numbers of premature deaths prevented or extra years of life added for certain locales, but they could not be added up to one overall number of lives saved worldwide, Wilkinson said. Still, he added, "the numbers would be substantial, would certainly be in the millions."
For example, switching to low-polluting cars in London and Delhi, India, would save 160 lost years of life in London and nearly 1,700 in Delhi for every million residents, one study found. But if people also drove less and walked or biked more, those extra saved years would soar to more than 7,300 years in London and 12,500 years in Delhi because of less heart disease.
Another study found that reducing - though not eliminating - meat consumption would decrease heart disease roughly 15 percent in England and in Sao Paulo, Brazil. Meat consumption is a global warming issue because large livestock farms emit large amounts of the potent greenhouse gas methane.
Sometimes climate change efforts could add to health problems, such as certain home energy efficiency improvements that might seal houses so much that they add to deaths from radon and secondhand smoke exposure, Wilkinson said. But those are offset by other health benefits, he added.
Outside scientists praised the studies and said the research was sound.
"The science is really excellent; the modeling is quite good," said Dr. Paul Epstein of the Harvard School of Medicine's Center for Health and the Global Environment. "It really takes the whole field a step farther."
However, Portier and Wilkinson concede that getting people to eat less meat and to exercise more would be tough to achieve.
"We really have to change our lifestyles," said Portier, who is eating less meat and hopes to soon bicycle more. "I can't help but hope that we can."