A couple of weekends ago, thermometers in Denver -- average annual temperature 50 degrees -- registered 101 degrees. Around the same time in Phoenix -- average annual temperature 75 degrees -- the temperature topped 110 degrees.
That average temperature difference matters when it comes to heat-related mortality of older residents, finds recent research in The Review of Economics and Statistics. The upshot: People over age 65 are more likely to die during hot days in parts of the U.S. that are colder, on average, than in places that are hotter. It’s a counterintuitive finding, according to one of the authors, David Molitor, assistant professor of finance at the University of Illinois at Urbana-Champaign.
“People have conjectured that maybe warming is good for cold places and bad for hot,” he says. “We find the opposite: If places don’t adapt, then getting warmer is really bad in cold places. Even moderate heat is quite deadly, whereas hot places are well-adapted to heat.”
Take, for example, adaptations like home air conditioning. Another recent study investigating the relationship between temperature and mortality reaches the same conclusion. It’s a massive multiyear study, released in July as a National Bureau of Economic Research working paper, from a consortium of economists and climate change scientists, with analyses based on data from 40 countries.
In one analysis, the authors take a particular look at Seattle and Houston. In an average year, Seattle records less than one day in which the average temperature rises above 85 degrees, according to the paper. Houston has about eight such days per year. Any individual hot day, the authors find, leads to more deaths in temperate Seattle than in hot Houston.
“In Houston, everyone has air conditioners,” says one of the authors, economist Amir Jina at the University of Chicago. “In Seattle, no one has air conditioners. You’d expect the impacts to be worse in Seattle than Houston for an extremely hot day.”
As wildfires scorch millions of acres of forest in Oregon, California and Washington, these two papers -- one focused on the U.S., the other on the world -- offer previously unseen detail on the intersection of temperature, mortality and place.
What, me worry?
Scientific models developed in the early 1990s brought together economic and climate data, revealing for policy makers and the public the global economic costs of doing nothing on climate change. Since 1980, the cost of extreme weather exacerbated by climate change has topped $1 trillion in the U.S. alone, according to the Fourth National Climate Assessment. The Dynamic Integrated Climate Economy model is one of the most famous, developed by Yale University economist William Nordhaus.
DICE is the pioneer of what’s called integrated assessment modeling. There are now at least 60 individual climate-economy models covering various world regions and periods of time. Nordhaus won the 2018 Nobel Prize in economics for his path-breaking work bridging macroeconomics and climate change science.
One shift happening now at the intersection of climate change and economic modeling is that researchers are incorporating ever-more-granular data to study ever-larger regions and answer ever-bigger questions. There has been an explosion of climate data available in the past decade. With improved computer processing power, researchers don't need access to huge servers. Laptops can handle that data.
Researchers can now show not only how climate change affects continents and the world from an economic perspective, but also how the distribution of those effects will be felt unequally from country to country and within regions of a nation -- even across zip codes.
Molitor co-authored the paper, “Adaptation and the Mortality Effects of Temperature Across U.S. Climate Regions,” with economist Garth Heutel at Georgia State University and Nolan Miller, business professor at the University of Illinois.
They base their analysis on data on dates of death and zip codes for everyone in the U.S. over age 65 who had Medicare coverage from 1992 to 2013. Heutel, Miller and Molitor combine those Medicare administrative records with climate change predictions from 21 models, an emissions scenario that assumes carbon dioxide emissions keep climbing throughout this century, and historical daily weather readings from the National Oceanic and Atmospheric Administration.
“We thought one thing that would be helpful to do is simply measure how health outcomes differ across climate regions,” Molitor says. “In the U.S., we have an enormous number of climates.”
The authors organized zip codes by average daily temperature. One third is made up of the warmest zip codes on average, one third is the coldest, and one third is in the middle. Mortality is lowest for the warmest third of zip codes on days when the average temperature is between 75 and 80 degrees. For the coldest third, the death rate is lowest on days when the average temperature is between 60 and 65.
But when the average daily temperature edges up above 75 degrees, “colder regions feature a stark increase in mortality,” the authors write.
Looking at the coldest tenth of zip codes, a day with an average temperature of 85 to 90 degrees increases mortality by 1.8 deaths per 100,000 Medicare beneficiaries. That temperature range bears almost no relationship with death rates for the warmest tenth of zip codes. Likewise, there’s a higher chance of death for older people when the temperature drops below freezing in places that are typically warm.
Using their detailed zip code-level data on the relationship between temperature and mortality, the authors find that if every place in the country adapts to its unique changing climate by the end of the century, mortality rates for people over age 65 can be curtailed.
Business as usual
Heutel, Miller and Molitor assume a “business as usual” carbon dioxide emissions scenario, in which the amount of energy lingering in the atmosphere from burning fossil fuels and other carbon-intensive activities continues to rise, leading to an average annual temperature increase of 8 degrees nationwide toward the end of the century.
Climate researchers Zeke Hausfather and Glen Peters recently lamented in Nature the widespread use of this “business as usual” emissions assumption in climate modeling. They argue that “overstating the likelihood of extreme climate impacts can make mitigation seem harder than it actually is.”
It’s important to clarify that climate modeling typically isn’t intended to tell the future. The future is, by definition, unknowable. Climate models are meant to offer a range of scenarios to inform policy makers.
Climate researchers Christopher Schwalm, Spencer Glendon and Philip Duffy, writing in the Proceedings of the National Academy of Sciences, counter Hausfather and Peters: “It is meaningless to characterize a scenario as ‘misleading’ -- that assumes that we know the true future and are deliberately predicting a different one.”
For Heutel, Miller and Molitor, the takeaway is that if policymakers in cooler places aren’t adapting for what happens when their area gets warmer -- because they think warmer temperatures might actually be beneficial -- that’s a misguided approach, particularly when factoring death rates for older residents.
Adaptation can take many forms, but on an individual level it can mean running a window unit air conditioner. (Mitigation, another term that commonly crops up in climate change policy, refers to actions that don’t simply address the effects of climate change, but reduce and stabilize carbon emissions in the first place.) Planning for a changing climate is like taking out insurance, Molitor says. The worst case scenario might not happen, but it would be bad to be caught unprepared if it did.
“You can try to avoid it and try to prepare and adapt,” he says. “Our study suggests there is a lot of scope for adaptation, which is an encouraging thing if you think maybe governments won’t be able to coordinate. Local governments may be able to do things that may be effective.”
Spillover: Climate change doesn’t care about national boundaries
There are numerous types of climate change -- not just warming. None of them respect political boundaries. As polar ice melts and sea levels rise, coastal cities in countries across the world stand to be inundated with water. Analyses on life and death say something about whether people live or die, but they don’t say anything about quality of life. The outdoorswoman sitting in air conditioning all day isn’t necessarily living her best life.
That point about climate change not respecting political boundaries is where the NBER paper comes in. “Valuing the Global Mortality Consequences of Climate Change Accounting for Adaptation Costs and Benefits,” has 16 authors and is a product of the Climate Impact Lab, a collaboration of economists, climate scientists and other researchers from the University of California Berkeley, the University of Chicago, Rutgers University and the economic research firm Rhodium Group.
The authors use data from 40 countries broken into 24,378 individual regions where nearly 40% of the global population lives. They assume the same emissions and warming as Heutel, Miller and Molitor.
Despite having “the most comprehensive mortality data file ever collected,” the authors caution that there are “more than 4.2 billion people unrepresented in the sample of available data, which is especially troubling because these populations have incomes and live in climates that may differ from the parts of the world where data are available.” Based on the data they have, the authors produce some of the most current partial estimates of what’s called the “social cost of carbon,” with a focus on costs related to mortality.
Researchers for decades have used models like Nordhaus’ to estimate the social cost of carbon. It’s often meant to be an all-in-one measure that monetizes the costs of each additional ton of carbon dioxide on agriculture, health, flood risk, energy costs -- like people running air conditioners -- and other factors.
Federal government scientists are working on updating the definition of the social costs of carbon. For now, the Climate Impact Lab finds that each ton of carbon dioxide comes with a social cost from mortality of roughly $37, using 2019 dollars.
Every extra ton of carbon dioxide in the atmosphere adds up in life, death and economic terms. By 2100, the authors project extreme heat and cold could be responsible for about 85 deaths per 100,000 people globally. Those deaths equal a loss of about 3.2% of the world’s economic output. For comparison, the authors offer that the death rate of car crashes in the U.S. was about 11 per 100,000 in 2017. Under a lower emissions scenario, in which emissions start to decline after 2050, the death rate falls to 14 per 100,000 and the social cost of carbon falls to $17.
“Ton of carbon” is a standard measure in climate research. But it can be a little difficult to conceptualize. To put it in real terms, a ton of carbon dioxide is released when about 1,100 pounds of coal are burned. That might sound like a lot of coal, but it’s a fraction of the roughly 1.1 billion pounds burned in the U.S. for energy in 2019, according to data from the Energy Information Administration. U.S. coal-fired energy producers emitted roughly 2.5 billion tons of carbon dioxide in 2018, according to EIA data.
Therein lies the first rub. There are about 2 billion air conditioning units in the world right now. By 2030, that number could jump by two-thirds, according to the International Energy Agency, an intergovernmental organization created in the wake of the 1973 global oil crisis. Indonesia and India are the fastest growing markets for air conditioners. Aside from the pollutants inside air conditioners, when people adapt to warmer temperatures by running air conditioners powered by coal, the adaptation ends up working crosswise to mitigation.
“One of the best ways we have to adapt -- it’s this cruel irony -- is to use more of the thing which is causing the problem, which is to use more energy,” Jina says. “Conceptually, it’s hard.”
‘An extremely broad waste management problem’
The second rub goes back to inequality. Without factoring in political will, countries that are wealthier will, broadly speaking, be able to create and implement adaptation and mitigation technologies and strategies more often and more comprehensively than countries that are less wealthy.
“What we have is an extremely broad waste management problem,” Jina says.
At the country level -- and even at the household level -- the wealthy use more energy than the less wealthy. Households with higher incomes produce 25% more greenhouse gas emissions from energy use than households with lower incomes, according to “The Carbon Footprint of Household Energy Use in the United States,” published Aug. 11 in the Proceedings of the National Academy of Sciences by Benjamin Goldstein, Dimitrios Gounaridis and Joshua Newell at the University of Michigan.
There’s a simple reason: Wealthier people tend to have bigger houses, which require more energy to heat, cool and light. They also have more money to pay for that energy.
Jina and his co-authors find, consistent with past research, that places that are hotter and less wealthy shoulder an outsized burden from climate change. For example, the authors project that Accra, Ghana will see its annual mortality rate jump 19% by the end of the century due to climate change. Oslo, Norway, by stark contrast, is projected to see a 28% decline in mortality.
“However, there is large variance across impact regions within each income decile, implying that some poor regions are projected to experience mortality rate declines, and some wealthy regions mortality rate increases,” the authors write.
That finding doesn’t run counter to the recent research from Heutel, Miller and Molitor. They look at one measure -- mortality for people over age 65 -- in one country, the U.S. The Climate Impact Lab research is global, covers countries at a variety of wealth levels and accounts for a variety of climate change costs.
The difference in scope doesn’t make one piece of research better or worse than the other. It means policy makers in the U.S. and around the world have a solid body of economic and climate science -- these papers being just two of the more recent examples -- to make adaptation and mitigation decisions tailored to local needs.
“The part a lot of policy makers and the public have missed is that climate change exacerbates inequality,” Jina says. “This is really going to challenge our ideas of fairness in the world. Beyond just having negative impacts, it will challenge how we think about what our society should look like globally and domestically.”
For more on covering climate issues, check out our research roundup on how heat waves affect older people.