Kelley, who is based at the University of Nevada, notes that the Paris climate agreement describes a global warming of two degrees Celsius—3.6 degrees Fahrenheit—above pre-industrial levels as "dangerous." Many Americans, he notes, currently live in regions that are at least that much warmer than other parts of the country. (The temperatures over the contiguous 48 states range from 15 degrees Fahrenheit in Minnesota winters to 81 degrees during Florida's torrid summers.) So he combines National Oceanic and Atmospheric Administration temperature data with survey data to probe how much a two-degree increase would bother Americans.
The survey in question asked a national survey of more than 2,000 Americans to rate how satisfied they were with their summer and winter weather on a scale of 0 to 100. A 25-year old woman in Wisconsin, for example, rated winter in the Badger State at 0 points and summer at 90. Across the nation as a whole, Americans gave their summer weather an average rating of 67 and their winter weather 61. Each extra degree Fahrenheit reduced their satisfaction with summer by -0.82 points, and every higher degree Fahrenheit increased their satisfaction with winter by +1.03 points.
Northerners' feelings about their winters were somewhat negative, with more than 10 percent rating them at 0 points; 30 percent of Southerners scored their winter weather at 100 points. "Such warming will greatly increase Americans' satisfaction with winter weather, especially in the north, and somewhat decrease satisfaction with summer weather in both north and south," reports Kelley. "On balance the nation benefits slightly."
Using NOAA data, Kelley calculates that a 4-degree-Fahrenheit temperature increase would be the equivalent for a typical American of moving about 180 miles south. To experience an average of 4 degrees Fahrenheit warming, a Virginian like me would head for North Carolina. (My wife spent her childhood in North Carolina; it's not so bad.) As it happens, those of us who reside in the Old Dominion rate their summer and winter weather at 61 and 62 points, respectively; those smug North Carolinians correspondingly give theirs 72 and 70 points. Kelley reports that over the year as a whole, residents in warmer states are generally happier with their weather.
Next Kelley compares the weather satisfaction scores of states in comparable temperature bands. For example, the average yearly temperature of states like Minnesota, Maine, North Dakota, and Montana hovers around 44 degrees Fahrenheit; in Michigan, New York, Colorado, and Oregon, it's 48. Parsing the weather preferences in the survey, he finds that southerners' rising dissatisfaction with their climate-change-induced higher summertime temperatures is more than counterbalanced by the increased happiness of northerners with their warmer winters. A four-degree increase in both summer and winter temperatures produces an almost two-point increase in year-round happiness with the weather. More surprisingly, an eight-degree increase in heat yields a two-point increase in weather satisfaction.
Kelley then turns to life-satisfaction surveys to try to figure out what monetary value Americans would put on improved weather. Through a complicated process, he calculates that a one-point increase in weather satisfaction is equivalent to about a $3,000 annual increase in income. "By our (admittedly rough) estimates for 'dangerous' warming's effect over the year as a whole, combining its gains for winter and losses for summer and aggregating over the US as a whole, the $3000 gain from a single climate satisfaction point comes to something like 2 or 3 percent of GDP," he notes. "Two climate satisfaction points, our best guess for the US, would be twice that."
Kelley next points out that the Intergovernmental Panel on Climate Change estimates that the losses from a two-degree Celsius (3.6 degree Fahrenheit) average temperature increase would be around two percent of national income. "Thus the changes in the general public's climate satisfaction that we analyze in this paper appear to be, in and of themselves, at least as large as the combined financial implications of all other aspects of global warming," writes Kelley.
A study just last April in Nature more or less bolsters Kelley's conclusions. "We find that 80% of Americans live in counties that are experiencing more pleasant weather than they did four decades ago," the researchers report. "Virtually all Americans are now experiencing the much milder winters that they typically prefer, and these mild winters have not been offset by markedly more uncomfortable summers or other negative changes."
Kelley has a point when he observes that "the effects of the allegedly 'dangerous' 2 degrees Celsius (3 or 4 degrees Fahrenheit) of global warming seem in fact to be small—on average equivalent for a typical American to moving just 180 miles south. Few Americans would find moving from one state to 'dangerously' warmer state further south at all daunting; indeed many make such moves voluntarily over the course of their lives. These effects are not in any obvious way 'dangerous' for vast majority of ordinary citizens."
Now some caveats. As the climate warms, Americans may initially enjoy better weather, but Kelley's study conspicuously does not take into account other consequences of man-made global warming, such rising sea levels, changes in rainfall patterns, the possible inability of plants and animals to adapt, and so forth. In addition, the increase in temperatures down the road may be more than four degrees. As Kelley acknowledges, "Over two or three centuries...it might be a problem."
And if climate change projections are accurate, other parts of the world will not be as fortunate as the United States. According to a study in the February Proceedings of the National Academy of Sciences, climate models project that even a two-degree Celsius increase around the globe will bring large increases in the frequency of deadly heat waves by the middle of the century, afflicting more than 350 million inhabitants in such megacities as Karachi, Lagos, Kolkata, and Shanghai. Even more alarmingly, a 2015 study in Nature Climate Change projected that the temperatures and humidity around the Persian Gulf would rise so high by 2100 that the region would become uninhabitable because people would be unable to sweat enough to maintain their body temperatures. So some places won't have it as good as Virginia.
In the meantime, the best way to address the deleterious consequences of future warming is to adopt policies that speed up economic growth and technological progress, allowing us to adapt more easily to the changing climate.