Residents of the United States could experience a four-to-six-fold increase in extreme heat events as soon as the middle of the century.
Researchers at the National Center for Atmospheric Research (NCAR) and the City University of New York (CUNY) predicted these changes will occur as a result of global warming and population growth. The study highlights the need to look into what societal changes could help ease these impacts.
"Both population change and climate change matter," said NCAR scientist Brian O'Neill, one of the study's co-authors. "If you want to know how heat waves will affect health in the future, you have to consider both."
The increases in heat waves are expected to hit cities in the southern region of the country the hardest, this included cities such as: "Atlanta, Charlotte, Dallas, Houston, Oklahoma City, Phoenix, Tampa, and San Antonio."
To make their findings, the researchers looked at 11 different high-resolution simulations of future temperatures across the United States between the years of 2041 and 2070. They also used a new demographic model to determine how the U.S. population will grow during the same time period. Total exposure to extreme heat was calculated in "person-days" by multiplying days that temperatures will exceed 95 degrees Fahrenheit in a region with the number of people who live there.
The study determined average annual extreme heat exposure will be between 10 and 14 billion person-days during the study period, compared with the average of 2.3 billion person-days seen between 1971 and 2000. About a third of this increase is believed to be directly linked to global warming, and another third to population change. The final third was attributed to interactions between global warming and changes in population size and distribution.
"We asked, 'Where are the people moving? Where are the climate hot spots? How do those two things interact?'" said NCAR scientist Linda Mearns, also a study co-author. "When we looked at the country as a whole, we found that each factor had relatively equal effect."
While some areas of the U.S. are more vulnerable to these heat events than others, some increases in extreme heat exposures were predicted for every region of the country. The researchers noted that there is a difference between exposure and vulnerability to high temperatures.
"Our study does not say how vulnerable or not people might be in the future," O'Neill said. "We show that heat exposure will go up, but we don't know how many of the people exposed will or won't have air conditioners or easy access to public health centers, for example."
The researchers hope the study will inspire scientists to incorporate societal factors, such as changes in population size and composition, into their climate models more frequently.
"There has been so much written regarding the potential impacts of climate change, particularly as they relate to physical climate extremes," said Bryan Jones, a postdoctoral researcher at the CUNY Institute for Demographic Research and lead author of the study. "However, it is how people experience these extremes that will ultimately shape the broader public perception of climate change."
The findings were reported in a recent edition of the journal Nature Climate Change and the simulation were produced as a part of the North American Regional Climate Change Assessment Program.
