While global warming sometimes appears as a distant or abstract threat, new research throws the phenomenon to the test, to death or to perpetuity. He predicts that without significant progress in efforts to reduce greenhouse gas emissions, extreme heat waves could kill thousands of people in major US cities.
If the global average temperature rises by 3 degrees Celsius (5.4 degrees Fahrenheit) above pre-industrial levels – which some scientists believe is likely if countries honor only their current commitments to reduce emissions – a major heat wave could kill nearly 6,000 people in New York. Similar events could kill more than 2,500 in Los Angeles and more than 2,300 in Miami.
But the new research also indicates that if the US and other countries take aggressive action to limit global warming, many of these extreme heat deaths could be avoided.
"There is indeed still hope and a very small window of opportunity" to keep global warming below international targets and prevent some heat-related deaths, said Eunice Lo, a leading climate scientist. the University of Bristol in the United Kingdom. co-author of an article describing the research, published June 5 in the journal Science Advances.
For the research, Lo and his collaborators focused on the so-called "1 in 30" events, strong heat waves that occur every few decades and that pose a major threat to children, older adults, workers outdoors and people living in poverty. Heat waves are particularly dangerous in urban areas, where paved surfaces and very compact buildings create extremely hot "urban heat islands".
To see how global warming could affect mortality rates, scientists have simulated three possible climate scenarios. In one of these countries, the countries of the world have only the bare minimum to reduce their carbon emissions, thus limiting the rise in the average temperature of the planet to 3 degrees Celsius by 2100. In the other two scenarios, countries go beyond their efforts by limiting the average increase in temperature to 2 or 1.5 degrees Celsius.
For each scenario, scientists used climate models to predict hot weather temperatures in 15 major US cities, including Detroit, Philadelphia, Los Angeles, Miami, and New York. Then, they estimated how many people would die at each temperature based on actual data from decades of heat-related deaths.
At 3 degrees of warming, scientists estimated that a heat wave once per generation could kill more than 20,000 people in 15 cities. Keeping warming at 2 degrees could save hundreds or thousands of lives in most cities, the study showed. With a warming of 1.5 degrees, more than half of the deaths expected in some cities could be avoided.
"You may be thinking, what is the difference of 1.5 degrees in human lives?" Said Lo. "In reality, thousands of lives in a year can be saved in a city. Achieving the 1.5 degree goal is essential and would be very beneficial to public health in the United States. "
Aaron Bernstein, co-director of the Center for Global Health and Environment at T.H. at Harvard. The Chan School of Public Health praised the study for its city-by-city breakdown of preventable heat-related deaths. He called it "a much more sophisticated and precise way of looking at the issue" than relying solely on national data.
Surprisingly enough, Dr. Bernstein explained that the study might have underestimated the impact of heat waves by not taking into account non-fatal heat-related injuries, which send patients to US emergency rooms about 65,000 times each summer. "They focused on heat and death," he said of the researchers, "but there are many things that are bad for people who do not die."
Lo said the study had some limitations, including the fact that scientists were unable to predict what the population of each city – including the number of elderly and low-income residents – could look like. end of the century. Cities and humans themselves could also adapt to rising temperatures, resulting in fewer deaths than expected.
Shubhayu Saha, a climate and health scientist with the Center for Disease Control and Prevention, declined to comment on the new study, but acknowledged the risk posed by rising temperatures. "According to forecasts, the number of deaths and diseases will increase in the years to come, as the summers will lengthen and the heat will become more intense," he said.
Many municipal health departments are opening climate controlled air conditioning centers during the summer months for those who do not have air conditioning at home. And the Environmental Protection Agency recommends that cities issue warnings before heat waves, create more green space to mitigate the heat island effect, and educate the most vulnerable people about heat-related illness and death. .
Vulnerable or not, "we will all be affected or already affected by climate change," said Lo, calling for action to bring climate change to the 1.5 ° C threshold.
"We are talking about human lives," she added. "Not just the temperature changes, but actually our lives."
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