Human population in the contingent U.S. has shifted to warmer and drier areas over the last century, a study shows. Though environmental implications of this pattern cannot be proven without further research, scientists can speculate with some confidence.
Jason Samson an ecologist from the Department of Natural Resource Sciences at McGill University in Canada, and his fellow researchers used spatially explicit models to see how climate, income and biophysical factors were related to demographic change between the years 1900 and 2000.
The researchers used census data, and weather patterns collected from every county–almost 3,000—in the U.S. over the course of the century and pointed out a strong correlation between climate patterns and population growth.
The study showed that more people are concentrated in areas along the southern coast such as Florida, Texas and California, than in the northern regions. Due to this shift, an average American today experiences a climate that is more than 2.7 degrees warmer than it was a century ago, which could have environmental consequences.
Although Samson hasn’t conducted research on the implications of this shift, he said he can speculate.
“The main concern is about the energy required to sustain a demographic shift in warmer and drier regions,” Samson said. “The cost of cooling a building is much higher than the cost of warming it, so higher population size in warm environments creates more greenhouse gas emissions. Living far away from where food is produced also requires more greenhouse gas emissions through transportation.”
He said that these increased greenhouse gas emissions are creating a positive feedback cycle. The emissions cause temperatures to increase, meaning humans will need to use more energy to cool themselves. This, in turn, increases emissions further.
He also said this shift may explain water concerns about aquifers, particularly in the West. He said the supplies of the main reservoirs, Mead and Powel, are decreasing rapidly.
“The amount of water diverted to agriculture and urban usage is taken from ecosystems downstream,” Samson said. “We can thus speculate that the current water diversion for human consumption, directly and indirectly, will disturb the ecological reality in these regions.”
Though causality cannot be proven among the factors that were considered in the shift, Samson has a hunch that fossil fuels and technology allowed humans to move to these “unsuitable climate conditions.”
Samson said this research will be important to regional policy makers, since climate doesn’t change in a uniform way and each region experiences it differently.
“Policy makers should thus consider regional demographic growth planning as a way to mitigate climate change vulnerability in the same way that they consider lowering greenhouse gas emissions,” he said.
The study, “Demographic Amplification of Climate Change Experienced by the Contiguous United States Population during the 20th Century,” can be read here.
Citation: Samson J, Berteaux D, McGill BJ, Humphries MM (2012) Demographic Amplification of Climate Change Experienced by the Contiguous United States Population during the 20th Century. PLoS ONE 7(10): e45683. doi:10.1371/journal.pone.0045683
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