Road markings appear distorted during a heatwave in New Delhi, India, 27 May 2015. EPA/HARISH TYAGI

Climate change could pose a major health risk to the planet’s human population over the course of the 21st century, says a major new report from the medical journal the Lancet’s Commission on Health and Climate Change. But at the same time, the document adds, addressing the problem could confer a vast health benefit.

The report, which lists 45 authors from Europe and China, follows on a similar 2009 study by another Lancet commission, which had found that a warming climate would pose “the biggest global health threat of the 21st century.” That conclusion hasn’t changed — but the science has been considerably updated in the new report, and the health benefits of climate change mitigation become a chief focus.

“The implications of climate change for a global population of 9 billion people threatens to undermine the last half century of gains in development and global health,” says the new document, noting further that “future projections represent an unacceptably high and potentially catastrophic risk to human health.” But it also adds that “tackling climate change could be the greatest global health opportunity of this century.”

The report emerges just before a Tuesday White House summit on climate change and public health, to be attended by Surgeon General Vivek Murthy and EPA administrator Gina McCarthy. In rolling out a new initiative to highlight the links between climate and health in April — of which the summit is part — President Obama commented that “there are a whole host of public health impacts that are going to hit home. So we’ve got to do better in protecting vulnerable Americans.  Ultimately, though, all of our families are going to be vulnerable.  You can’t cordon yourself off from air or from climate.”

The most obvious health impact of a warming climate is, of course, more dangers from extreme heat. The new Lancet Commission report finds a “a well-established relationship between extreme high temperatures and human morbidity and mortality,” adding that there’s “strong evidence that such heat-related mortality is rising as a result of climate change impacts across a range of localities.” In particular, it cites the summer of 2010 Russian heat wave, which — in addition to the compounding effects of poor air quality — caused 11,000 additional heat-related deaths, compared with those that occurred in the region the previous summer.

Among those who suffer from extreme heat, one group of particular concern are outdoor workers. “There’s a limit to how much work we can do in heat,” says Ian Hamilton, a professor at the University College London and a co-author of the report. “Thousands of Indians have died as a result of heat stress” in the recent Indian heat wave, Hamilton added.

The new study finds that even as the world warms, exploding populations and greater urbanization will further increase the numbers of people exposed to heat extremes.

But scorching heat is only the most obvious way that climate change imperils health. There are also health dangers posed by changes to extreme weather events, or by increasing incidence of drought. And there’s the risk of vector-borne diseases changing their ranges or becoming more widely transmitted.  Particular diseases where this could occur include West Nile Virus and Hantavirus, according to the report.

Some climate-driven health risks are considerably more indirect than others. For instance, if there is any threat to food supplies due to climate change — for instance, if a warmer world can’t produce as much of staple crops like corn or wheat — then there could be severe consequences for nutrition. “For every degree greater than 30°C, the productivity of maize production in Africa might be reduced by 1% in optimum conditions and 1·7% in drought, with a 95% chance of climate change-related harm to the production of South African maize and wheat in the absence of adaptation,” notes the study.

Fortunately, doing something to cut emissions not only reduces these risks, but also has knock-on positive health effects — for instance, by cleaning the air and thus cutting down on  particulate pollution, which has its own health cost. “Fine particulate air pollution is estimated to be responsible for 7 million additional deaths globally in 2012, mainly due to respiratory and cardiovascular disease,” notes the Lancet commission report. It calls for a “rapid phase out of coal from the global energy mix,” noting that proposed 2200 new coal plants to be constructed worldwide will have many deleterious health consequences.

Overall, the report serves to amplify an increasing trend towards framing climate change around health consequences — a strategy that communications scholars have found could help open minds. “When climate change is framed as a health issue, rather than purely as an environmental, economic, or technological challenge, it becomes clear that we are facing a predicament that strikes at the heart of humanity,” add Lancet Asia editor Helena Wang and editor Richard Horton in a commentary on the commission’s report.

“Health puts a human face on what can sometimes seem to be a distant threat.”

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