By using census data and information about weather patterns (temperature and rainfall) gathered from the nearly 3 000 counties in the U.S. over the course of the century, Samson and his colleagues were able to show the predominant importance of the correlation between climate and demographic growth. Moreover, in the study just published in PLOS ONE, the researchers found that population growth was more correlated with climate than income, urbanization or food production.
The researchers found that the average American today not only lives in a drier environment than they did a century ago, but that they have also experienced a temperature increase of over 1.5° Celsius or 2.7° Fahrenheit over the last century. That represents a six-fold increase compared to the temperature change across the US during the same time period.
More and more Americans now live in the warm southern belt of the country that extends from California to Florida, and includes cities such as San Diego, Austin (the third largest growing city in the nation between 2000-2006) and Tampa. The researchers also point to the fact that demographic growth in these warmer and drier climates within the country, and the trend towards urbanization and agglomeration, has been happening at an accelerating pace over the course of the twentieth century, and is particularly noticeable within the last thirty years.
Although the researchers were able to show such a significant correlation between climate and demographic growth, they caution against thinking of climate as a strong predictive factor in determining population movements. They also caution that this concentration of population in warm, dry areas is likely to have a significant effect on human well-being in these locations due to monetary, and environmental factors (such as growing size and intensity of heat islands, increasing stress on limited water supplies, and the high cost of using air conditioning). And they suggest that policy makers may be well advised to consider this information as they plan for the future given the context of global climate change.
The research was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC).