InsightsApril 26, 2023

Michael Greenstone Testifies on the Health Impacts of Climate Change

In a congressional hearing convened by the US Senate Committee on the Budget, Climate Impact Lab co-founder Michael Greenstone provided expert testimony on the Lab's research on the global mortality and health impacts of climate-driven temperature change.

Testimony by Michael Greenstone

Thank you, Chairman Whitehouse, Ranking Member Grassley, and members of the Committee for inviting me to speak today.

My name is Michael Greenstone, and I am the Milton Friedman Distinguished Service Professor in Economics and Director of the Becker Friedman Institute and Energy Policy Institute at the University of Chicago. I also serve as co-director of the Climate Impact Lab, a multi-disciplinary collaboration of researchers working to quantify the long-term impacts of climate change. My research focuses on estimating the costs and benefits of societies’ energy and environmental choices.

I appreciate the opportunity to speak with you today about the projected health costs of climate change and the impacts of climate change on the broader economy.

Over the last year, the world has been experiencing record hot temperatures: Summer 2022 was the second hottest ever recorded in the Northern Hemisphere. A weather station in Death Valley, California, clocked a scorching 53°C (127°F) in September, one of the hottest temperatures ever observed on Earth. Officials from Delhi to Tokyo to Baghdad, cities where past heat waves have claimed hundreds of lives, are bracing for dangerously hot periods. And yet, this is nothing new. Year after year heat records are broken all over the world.

Temperature’s toll on public health, particularly the toll from extreme temperatures, is likely to be one of the dominant costs of climate change. Thus, given our ability today to alter the path of temperature change through the release of greenhouse gases, understanding the relationships between temperature change, mortality, and the monetary costs of this mortality, is essential to determining appropriate responses to climate change. So, what impact will temperature have on public health, and how much will it cost? The paper, “Valuing the Global Mortality Consequences of Climate Change Accounting for Adaptation Costs and Benefits” that I authored with my colleagues at the Climate Impact Lab, and which was published in The Quarterly Journal of Economics last year, addresses these critical questions.

I want to emphasize from the outset one data challenge with the paper’s results that is due to the state of climate science. This research produces local (e.g., at the U.S. county level) climate impact estimates and thus requires local projections of what will happen to temperatures in the future. Such climate projections are only available for two climate scenarios: RCP8.5 which is considered a “high-emissions scenario” and RCP4.5 which is considered a “moderate-emissions scenario.” Given current trends and policies, the high-emissions pathway likely overstates the growth of emissions, while the moderate-emissions pathway likely understates it. Throughout the testimony I will present results using both pathways, but the true impacts of climate change from our current trajectory are likely to lie between the estimates based on these two emissions pathways.

In the remainder of my statement, I will make the following points:

1. To measure the impact of climate-driven temperature changes on mortality risk, my colleagues and I compiled the largest sub-national vital statistics database in the world, detailing 399 million deaths across 40 countries accounting for 38% of the global population. We divided the world into more than 24,000 regions that are each about the size of a U.S. county.

2. We found that the global mortality risk is projected to increase by 85 deaths per 100,000 people by 2100 under the high-emissions scenario in which average global temperatures increase by around 3.7°C (6.7°F) relative to 2001-2010 temperatures. This is greater than the current global mortality rate—66 deaths per 100,000 people—from all infectious and parasitic diseases combined (excluding COVID-19). Under the moderate-emissions scenario—which is expected to increase temperatures by 1.6°C (2.9°F)—the global mortality risk is projected to increase by 14 deaths per 100,000 people, comparable to the global mortality rate from diabetes (19 per 100,000). The mortality consequences will be the largest in places that today are hot and/or poor.

3. In the United States, and under the high-emissions scenario, the mortality risk is projected to increase by 10 deaths per 100,000, about on par with our current fatality rate from auto accidents. Many areas will experience mortality risks that are significantly higher, including areas represented by members of this committee, which I will detail. In contrast, some areas will benefit as the number of deadly cold days declines, but again on average mortality risk will increase. Although the average mortality risk in the United States under the moderate-emissions scenario is projected to be essentially unchanged, there remain substantial geographic differences in these impacts, with many areas expected to see sizable increases in mortality risk and others expected to see declines.

4. On our current emissions trajectory—which lies in-between these two representative scenarios—we can expect climate-induced mortality risk to be in-between the two estimates. In this regard, policy has the potential to deliver some of the most significant public health gains in human history. Bringing global emissions down to moderate levels—not even as low as the Paris Agreement’s long-term targets—would reduce expected warming by around 2.1°C (3.8°F) at the end of the century and the attendant global mortality risk by 83% compared to the high-emissions pathway. As I highlighted above, under this moderate-emissions scenario, the total mortality risk due to climate-induced temperature changes would be eliminated in the United States.

5. This research is the basis for the new social cost of carbon estimates showing that the Trump and Obama administrations have underestimated the full social cost of carbon, in the former case dramatically so. As a part of a recent rulemaking, the Environmental Protection Agency (EPA) has proposed updating its estimate of the social cost of carbon to $190 from the Biden administration’s interim value of $51. This revision is an accurate reflection of recent advances in the literature on climate change and its economic impacts and incorporates recommendations made by the National Academies of Science, Engineering, and Medicine in 2017 (U.S. EPA 2022). The advances include those detailed in this testimony.