Two months ago, climate scientists studying US cities found that global warming could produce killer heat waves causing thousands of excess deaths during unusually hot summers like the one now affecting the eastern US and much of Europe.
Now, researchers have found that China faces an even worse problem – not just a few thousand extra deaths in unusually hot summers, but tens of thousands of additional deaths each year. And the problem, they say, will kick in at much lower rates of global warming than those predicted to endanger US cities.
Part of the problem, write Yanjun Wang of Nanjing University of Information Science & Technology and colleagues, in the journal Nature Communications, is that temperatures in China have been increasing faster than the global average.
But it isn’t the rise in average temperature that is the true problem, Wang’s team writes, so much as the fact that this rise is accompanied by an increase in the number of dangerously hot days.
In Chinese cities, they say, global warming of 1.5° degrees Celsius from pre-industrial levels (the Paris Agreement’s most ambitious not-to-exceed goal) could produce a 32.6% increase in the number of dangerously hot days.
An increase of 2.0 degrees (the Paris Agreement’s less-ambitious back-up goal) could produce a 45.8% increase.
Combining that with heat-fatality data from 27 large Chinese cities, the researchers calculated heat-death rates per year under each warming scenario, then extrapolated them to the rest of China’s 831 million city dwellers.
Their conclusion was that the difference between 1.5° degrees and 2.0° degrees matters – a lot. Even at 1.5° degrees, they found, China would experience a substantial increase in the number of annual deaths from heat. But at 2.0 degrees it would be substantially worse, with at least 27,900 extra deaths per year due simply to that extra 0.5 degree.
Other scientists are impressed.
One of the more important findings, says Eunice Lo, a climate scientist at the University of Bristol, UK, and co-author on the US-cities study, was that the new paper found that Chinese heat deaths could be reduced by about 50% by an increase in “adaptation” methods.
These would include such polices as increasing the use of air conditioning, encouraging people to change their activity patterns on hot days, and redesigning buildings to reduce their tendency to overheat. “I think this really highlights how beneficial adaptation will be to China’s public health,” she says.
Ethan Coffel, a climate scientist at Dartmouth College, New Hampshire, US, agrees. One of the main differences between China and the US, he says, is that China has a lot less air conditioning than America. “It’s also low in Europe,” he adds, “which contributes to the high death counts there in recent heat waves.”
Another problem, Coffel says, is that the same weather patterns that cause heat waves often cause poor air quality as well, a concern in China’s notoriously polluted metropolises. “The two are closely related, he says. “Pollution and heat will compound to increase health problems.”
But the study’s main finding remains the revelation of just how many extra deaths can result from a mere 0.5-degree difference in global warming. “This kind of study highlights the large differences in impacts that result from a seemingly small temperature change,” Coffel adds.
Vivek Shandas, an urban climatologist at Portland State University, US, adds that the study offers a sobering perspective of the scale of the worldwide challenge posed by global warming. “What in China may be 28,000 additional deaths per year, can easily equate to hundreds of thousands, globally,” he says.
Worse, he says, these risks are not borne by everyone, equally.
“We know from past studies of heat-related mortality that those with the least access to resources – financial, logistical, and/or social support – are the first to die. Those who have access to air conditioning and other avenues to stay cool during extreme heat are largely protected.”
Nor, he says, are the direct effects of heat the only ones that can be deadly. “Secondary effects, such as increase in forest fires and the related generation of particulate-matter pollution can further accelerate the loss of life,” he says. “We need further research to tie together how the cascade of impacts will ripple through society.”
Meanwhile, much as Wang’s study has broken new ground by carrying climate-death research to the world’s second-largest economy, that’s just the beginning.
With more than 1.3 billion people, India is poised to overtake China as the world’s most populous country, and its tropical location makes it prone to heat waves that would make most of us blanche.
“It has among the highest levels of heat stress in the world, and few have air conditioning,” Coffel says. “I would imagine that the impact differences between 1.5° degrees and 2.0° degrees would be even larger there than in China.”