Here's another health danger climate change will deliver in the coming years: New research warns that back-to-back heat waves that go on for days will become more common as the planet warms.
The elderly and the poor will be the least prepared to weather this threat, the investigators noted. But hospital ERs and emergency service providers will also be vulnerable to the public health havoc that such "compound heat waves" will likely inflict.
Significantly more common events
"By compound heat wave, we mean multiple heat waves – or possibly individual extremely hot days – occurring one after the other separated by short cooler breaks," explained study author Jane Wilson Baldwin. She's a postdoctoral research associate with the Princeton Environmental Institute in New Jersey.
An example, Baldwin said, would be five extremely hot days, followed by a respite of a couple of cooler days, and then three more extremely hot days.
Such repetitive scorchers are not confined to some distant future, the study found. They are already here, with heat waves and droughts currently pegged as the direct cause of roughly 20% of natural disaster deaths in the continental United States, more than any other single natural cause.
"However, these events will become significantly more common with global warming," noted Baldwin.
"In the present climate, only about 10% of heat waves exhibit these compound structures. Without drastic changes to carbon emissions, we project that by 2050 that proportion should rise to about 30%, indicating a dramatic change in the character of heat waves, and possibly how society needs to prepare for them," she said.
The study looked at a series of climate simulations generated by the US National Oceanographic and Atmosphere Administration's Geophysical Fluid Dynamics Laboratory, in conjunction with the Princeton Environmental Institute and its Atmosphere Administration's Geophysical Fluid Dynamics Laboratory.
Heat waves were minimal
The simulations examined weather patterns dating as far back as 1861 and as far ahead as 2100. They used two possible carbon dioxide (CO2) emission scenarios: one with levels steady at 1990 numbers (which have long since been exceeded), and another in which 1990 levels doubled.
At 1990 levels heat waves were minimal, adding up to about 10 days per summer, with only 10% subject to compound heat waves.
But in the doubling scenario, the number of heat wave days was pegged as eventually rising sevenfold, with tropical regions most at risk. A quarter of those days were subject to compound heat wave cycles.
Overall, heat waves were projected to become more common and to last longer, with fewer cool days in between.
Baldwin and her colleagues reported their findings recently in the journal Earth's Future.
For now, the team "stopped short of directly quantifying the human impacts of these events," noted Baldwin.
Changes locked in
But grave public health results are a distinct possibility. For example, an overtaxed electric grid may lead to increasingly frequent and lengthy blackouts and brownouts, rendering air conditioners useless, and leaving increasing numbers of people – particularly seniors – without access to lifesaving cool shelter. This may also be accompanied by a weakened food supply chain, due to the heat-prompted withering of agriculture and livestock resources, Baldwin said.
What's more, over the next few decades the projected heat wave trends are likely unavoidable, she said.
"Global warming and heat wave changes through 2050 are essentially locked in," Baldwin said. And that means adaptation is key, "such as increased AC and improved building ventilation; staying in shady, cool places and drinking more water; [and] hospital wards preparing for potentially more frequent heat stress victims".
The problem is that "this adaptation is likely to be relatively easy for rich countries and people, and much harder for the poor and otherwise socioeconomically underprivileged, who already suffer the most from heat waves in the present," Baldwin explained.
Additional actions required
Kristie Ebi is director of the Center for Health and the Global Environment at the University of Washington in Seattle. She agreed that going forward, "individuals and communities need to be better prepared to manage temperatures outside the range of what we consider normal.
"The greenhouse gases in the atmosphere will increase the number and intensity of heat waves over the next couple of decades," Ebi said.
"Based on the current number of illnesses and deaths during heat waves," Ebi added, "it is reasonable to assume the numbers would increase with more compound heat waves, if additional actions to increase awareness and preparedness are not taken."
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