Life and Death in Our Hot Future Will Be Shaped by Today’s Income Inequality

By Eric Roston, Paul Murray and Rachael Dottle

August 3, 2020, 3:00 AM EDT

It’s one of the scariest questions facing billions of humans on a hotter planet: How many of us will die from extreme heat in the decades ahead?

Your future risk of dying from heat will be determined more than anything else by where you live and the local consequences of today’s economic inequality. That’s the conclusion of a major paper released today by the Climate Impact Lab, a research consortium that spent years mapping the relationship between temperature, income, and mortality. People in poor regions who benefit less from investment in air conditioning, protective infrastructure, and elder care will die from extreme heat at much higher rates, even compared to wealthier peers who experience similar hot temperatures.

The researchers from the Climate Impact Lab determined that the toll from future heat will be far worse than expected, with the global annual mortality rate at the end of this century rising by 73 deaths per 100,000 people solely from excess heat. That’s a death rate comparable to the 72 per 100,000 that Arizona has seen from Covid-19 since January. “The mortality risks from climate change are about an order of magnitude larger than previously understood,” says Michael Greenstone, an economics professor at the University of Chicago and a co-director of the Climate Impact Lab. “I really think that shouldn’t be missed.”

The results emphasize the life-saving power of income growth that drives investment into climate adaptation. Economic development can reduce projected mortality from extreme heat at the century’s end by about 60%, according to the Climate Impact Lab, a finding that translates into the possibility of saving millions of lives.

Economic Growth Saves Lives

Projected changes in the rate of heat-related deaths

This means we can’t understand life and death on a hotter planet without first understanding inequality.

The impact of heat on the human body is an important part of the equation. Global average temperatures are already 1° Celsius warmer than previous centuries, and many studies project a catastrophic rise of 3°C by 2100.

An average doesn’t speak to what will be a dramatically unequal experience of future heat. Parts of the world have already warmed by more than twice the global average today. That trend will leave more people vulnerable to extreme heat, which has been linked to a 50% increase in mortality risk from stroke, cardiovascular disease and pulmonary conditions. In some regions working outside for a few hours will eventually carry grave risk. With enough exposure to extreme heat and humidity, the human body suffocates in its own skin because the air is too water-logged for sweat to evaporate.

But the deadly consequences of extreme heat are shaped as much by economics as biology. Imagine two nations—one wealthy and technologically developed, the other poor and without resources—that are suffering through an identical heat wave. Climate Impact Lab set out to understand the expected difference in death risk, after accounting for economic growth and adaptation. This is how the study works.

To measure the relationship between economic inequality and mortality rates over time, researchers first divided today’s world into 24,378 parcels, almost like census tracts. Each region contains roughly equal populations and comparable temperatures.

Plotting these regions on a chart shows the relationship between projected average temperatures and changes in death rates due to climate change between 2015 and 2099.

More than three-quarters of the world will see higher heat-related mortality risk by 2099. Khartoum, Sudan, is projected to suffer more than 400 deaths per 100,000 people. A hotter future also results in lives saved within regions that today experience mortality from extreme cold.

But the hottest places at the end of this century don't face equally elevated mortality risk from extreme heat. Climate Impact Lab found that future death rates are closely related to inequality in economic growth.

In our overheated future, this new research shows that people who live in similar climates will find income divides their fates. Regions with higher incomes over time are more likely to spend money on health and safety measures.

“These risks vary greatly, both across the globe and within countries,” Climate Impact Lab’s Greenstone says, “with the largest impacts being in today’s hot and poor locations.” Climate risks can also make inequality worse, as income and adaptation accumulate in regions best equipped to protect lives.

The last six years have been the hottest ever recorded, and 2020 will almost certainly take its place near the top. Killer heat is here.

Climate researchers see older people as a leading indicator for overall heat mortality because they are so sensitive to extreme temperatures. Vulnerability within elderly populations has already increased by more than 10% since 1990 in Africa, Southeast Asia, and the Western Pacific. A study last year in The Lancet found older people in Europe and the eastern Mediterranean experience some of the highest vulnerability to heat.

This century has already brought shocking heat-related death tolls in Europe (70,000 dead in 2003) and Russia (56,000 dead in 2010). Some 12,000 people in the U.S. die prematurely from heat-related causes each year, a figure that could increase as much as eightfold by 2099. In July 2020 alone, American authorities blanketed the population with warnings of record heat, Baghdad topped an unprecedented 51°C (125°F) and parts of the Arctic burned.

With the world heating so rapidly, conventional economic and public-health indicators can’t capture risk as it stands today. Trying to analyze risk out to the end of this century is far more difficult. Climate Impact Lab’s work was designed to help fill that gap. The new dataset, put together over years by researchers from University of Chicago, University of California, Berkeley, Rutgers University, and the Rhodium Group, makes it possible to compare risks faced among and within nations.

The global map produced by the researchers confirms an inescapable geographic inequality that will shape the warmer future. Climate change will lead to a future with more deaths in already hot places than in today’s colder regions. Accra, Ghana, can be expected to suffer almost double the global average risk by 2099, according to the Climate Impact Lab, reaching an average projected mortality risk of 160 per 100,000 people. Oslo, on the edge of the Arctic Circle in Norway, would see 230 fewer deaths per 100,000 thanks to warmer winters. This highlights the inequality: extreme heat carries a higher risk of death than extreme cold, and this disparity grows over time.

Inequality in heat mortality is most easily observable when comparing regions that have similar future climates but vastly different future incomes.

Places With Similar Climates But Very Different Incomes and Death Rates

Projected temperature and income in 2099 worldwide

Within borders, meanwhile, wealth inequality will create wildly varying climate risks for citizens of the same country. Indigenous and Black people in the U.S. today suffer the highest and second-highest heat-related death rates, respectively. That’s one reason why calls for climate justice to address the increased dangers faced by poor and minority populations have risen in parallel with the Black Lives Matter movement in the U.S.

Global inequality has been a dominant concern since the start of international climate policy debates, going back to the 1992 UN treaty assigning rich and poor countries “common but differentiated responsibilities.” That distinction was meant to recognize the far larger role played by wealthy nations in creating climate change, along with realism about who has the greatest means to address it. But the 2015 Paris Agreement softened that rich-poor distinction, establishing a voluntary network of national commitments to address a collective goal of limiting warming to 1.5°C.

The new research from Climate Impact Lab underscores that those facing the worst impact from global warming often benefited least from all the fossil fuel burned since the Industrial Revolution. Rising temperatures will only exacerbate today’s social and economic chasms, leading to more heat-related deaths—unless growth and investment can better equalize risks and reduce danger for everybody.

Residents cool off in a river canal during a heat wave Lahore, Pakistan, as temperatures reach 40°C. Photo by Arif ALI / AFP

The safest way to deal with climate damage is to prevent it from happening, which means cutting greenhouse-gas emissions to zero as quickly as possible. But one of the key findings of Climate Impact Lab’s work is that economic growth itself can reduce damage. The people of the future are assumed to be wealthier than we are today, and that blunts what would be an even more deadly toll from global warming.

One way to understand the power of economic growth is to model an outcome without it. The Climate Impact Lab devised a heat-mortality rate that assumed no growth and extreme heat conditions. In this beyond-worst-case scenario, excess heat by the end of the century causes more than 200 deaths per 100,000 people each year. That’s about the same as today’s worldwide death rate from stroke and heart disease combined.

But the hotter people of the future will, of course, spend more to protect themselves and use wealth that develops over the coming decades to deal with the deadly consequences of heat. That’s why rising incomes erase about half of the heat-related death risk, in Climate Impact Lab’s findings. The death rate falls further when adaptation is counted.

The Climate Impact Lab’s final estimates, in which growth and investment in resiliency cut the expected global death rate from excess heat by 60%, is a demonstration of the role that economic development will play in determining the impact of warming. The engine of development that unleashed dangerous emissions over the past two centuries has also lifted billions out of poverty and poor health. Its biggest job yet will be climate adaptation.

A camel herder guides his animals during a sandstorm at a camel market on the edge of Khartoum, Sudan. Photo by Ian Timberlake/AFP via Getty Images

The ultimate goal of this research is to put a dollar figure on every metric ton of climate pollution, one of the most fraught subjects in climate economics. “Everybody understands that there are damages associated with climate change,” says Climate Impact Lab’s Greenstone. “But it tends to get run over unless there is some empirical foundation that leads you to a particular value.”

Greenstone was an architect of U.S. carbon-price estimates as chief economist for President Obama’s Council of Economic Advisers, which established a social cost of carbon that today would be $50 per metric ton. The Trump White House has lowered this number to about $7, and a recent report by the U.S. Government Accountability Office concluded that the current price doesn’t reflect scientific recommendations. The “social cost of carbon” — the goal of Climate Impact Lab’s research — isn’t the same thing as a carbon tax; it’s an estimate developed to help government officials calculate the costs and benefits of proposed regulations, not a price actually levied on polluters.

Climate Impact Lab’s new estimate of the cost of climate damage attributable solely to heat mortality is $17.10 per metric ton of CO₂, if emissions are kept lower than expected, and $36.60 under a high-emission scenario. Other impacts, such as labor challenges or sea level rise will add further to the damage costs.

These figures join a world that now has more than 60 carbon pricing programs, some of which are levied on internal-combustion cars or the power sector, others on entire economies or international blocs, and several that are, like the social cost of carbon, research-based estimates. Each price is devised through its own blend of research, policy priorities, and political circumstances.

Climate Impact Lab uses two future pollution scenarios to determine its price. One sets very high emissions—higher even than the path the world seems to be on—and the other assumes emissions fall much faster than the current trajectory. Creating useful estimates of carbon pricing isn’t a matter of accurately predicting future emissions. “For many decision makers, the less-likely, higher-impact outcomes matter just as much, if not more, than those futures most likely to occur,” said the Rhodium Group in a recent paper.

Greenstone and his colleagues are taking an ambitious approach to estimating the social cost of carbon. Their method for pricing climate pollution includes unprecedented granular estimates of heat impacts on human lives and will eventually address damage to energy, agriculture, coastal property, labor productivity, and manufacturing. Once researchers know that full cost, the theory goes, policymakers and markets would be able to adjust the prices of fossil fuels to reflect the damage they inflict.

An estimated price per metric ton of CO₂ can also be used by planners to prioritize investment in climate adaptation. “Once there’s a concrete number,” Greenstone says, “it really organizes people’s thinking and helps lead to much more coherent policy.”

Solomon Hsiang, a professor of public policy at the University of California, Berkeley, and a co-director of the Climate Impact Lab, uses a what-if scenario to explain the need for understanding the cost of emissions. Imagine a startup that, for a fixed subscription fee, will revamp your everyday life to shield you from the impact of global warming. “We’re calculating what that startup should be charging you,” Hsiang says.

Not all economists take this approach. Some prefer to start with zero emissions by a certain date as a goal and then calculate the carbon price that would achieve that result. Others have adapted asset-pricing models to carbon dioxide, leading to a very high initial price that declines as pollution falls.

Climate Impact Lab’s methods have impressed leaders in climate economics. “This is extremely carefully done work,” says Maureen Cropper, an economist at the University of Maryland who co-led a 2017 National Academy of Sciences report on the social cost of carbon. “It’s really a model for how the social cost of carbon, or at least one component, should be calculated.”

While economists may disagree on their estimates, the actual price for a ton of CO₂ is clearly more than the default—zero—that prevails in nations such as the U.S. that don’t impose financial consequences on emissions. The grand project of steering economic growth and investment to protect people from the hotter future needs to translate the misery and damage from climate change into dollars. That’s the best way to understand the role development can play in shaping life on a warming planet.

This story has been updated to remove the death rate for Covid-19 in New York State in the third paragraph because the number excluded virus deaths in New York City. The update also added the Covid-19 death rate for Arizona.

Methodology

Data provided by Climate Impact Lab, prepared by Emile Tenezakis and Dylan Hogan.

The full mortality risk of climate change includes both changes in mortality rates and changes in expenditures on adaptation. Values are based upon emissions scenario RCP 8.5, socioeconomic scenario SSP3 (from the IIASA Shared Socioeconomic Pathways database), and are climate model-weighted means over 33 climate models and 1,000 Monte Carlo simulation runs.

The Climate Impact Lab research does not reflect the possibility of climate-related migration. As stated in their research, "existing empirical evidence of climate-induced migration, based on observable changes in climate to date, is mixed."

Projected per capita income is based upon socioeconomic scenario SSP3

Long-run average temperature based upon CCSM4 climate model and RCP 8.5 emissions scenarios

Lead image by Ashraf Shazly/AFP via Getty Images

Editors: Aaron Rutkoff and Yue Qiu

With assistance from Allison McCartney and Akshat Rathi

Life and Death in Our Hot Future Will Be Shaped by Today’s Income Inequality

Economic Growth Saves Lives

Places With Similar Climates But Very Different Incomes and Death Rates

Carbon Prices Worldwide