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Hotter Planet Means More Underweight Babies

If current projections of a warming planet prove accurate, researchers say the percentage of dangerously underweight newborns will increase significantly in the U.S. by the end of the century.
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To the dismay of environmentalists, climate change remains far down the list of public concerns. The longer heat waves, more intense storms and new habitats for disease-carrying insects will all impact human health, but the warnings haven't registered in the public imagination.

Arguably, what's needed is a sympathetic set of victims — utterly innocent creatures, preferably adorable, whose suffering can be directly linked to our actions, or inactions. Well, a research team led by economist Olivier Deschenes has identified just such a population.


If current projections of a warming planet prove accurate, the percentage of dangerously underweight newborns will increase significantly in the U.S. by the end of the century, according to a paper recently published in the American Economic Review. Due to the effects of hot temperatures, mean birth weights will decrease, on average, by 0.22 percent among whites and 0.36 percent among blacks.

"We find an estimated 5.9 percent increase in the probability of a low-birth-weight birth (defined as less than 2,500 grams) for whites and a 5.0 percent increase for blacks," the researchers conclude.

"I would expect these effects to be possibly much larger in poorer/hotter countries," added Deschenes, the lead author and associate professor at the University of California, Santa Barbara.

Deschenes and his colleagues came to these conclusions by comparing data on birth weights from 1972-1988 (from the National Center for Health Statistics Natality Detail Files) with the daily average temperature for each American county (as compiled by the National Climatic Data Center). They found a significant correlation between low-birth-weight babies and hot temperatures during the second and third trimesters.

"In addition to a predicted increase in average temperatures, many global climate change models contain the oft-overlooked prediction that there will be a large increase in the number of very hot days," the paper notes. "Our estimates imply that exposure to such extreme ambient temperatures will have deleterious effects on fetal health, causing a decrease in birth weight and an increase in the probability of low birth weight."

According to the March of Dimes, approximately 1 in 12 American babies is born with a low birth weight. These infants often suffer from serious health conditions, including respiratory, heart and intestinal problems and bleeding in the brain.

Deschenes concedes that an array of adaptations, such as people migrating away from regions that have become prohibitively hot, could temper these projected outcomes. Innovations in medicine and increases in average income may also mitigate these effects. Still, he and his colleagues are the first to notice this particular ill effect of a warming planet. How many others have yet to be discovered?

"There have been a few studies on the possible impacts of climate change on mortality, and generally the predictions go as you would expect: No very big predicted changes in mortality in the U.S., and larger impacts in poorer places," Deschenes said. "My paper on birth weight was a first attempt to look at non-fatal health conditions. That is where I would expect the U.S. to suffer its largest climate change impacts on health.

"For example, there could be a large increase in respiratory conditions prompted by the hotter weather, and so overall quality of life would go down, without a large increase in loss of life. But this is just a conjecture at the moment."

Nevertheless, the research is a reminder that climate change will have serious consequences for human health. The evidence may be as close as your crib.

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