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Economic development, air conditioning and adaptation to warming

Alicia Wongel, Lyssa M. Freese, Edgar Virgüez, Steven J. Davis, and Ken Caldeira · Environmental Research Letters 20, 124045 · 2025

Key finding. Populations in lower-income countries already experience the greatest number of high-temperature days without access to cooling and face the largest increases as the planet warms; avoiding an increase in such days would require those countries to sustain GDP growth rates exceeding their historical rates.

Two contour plots sharing axes of GDP per capita, on a logarithmic scale from 1,000 to 100,000 dollars, against cooling degree days from 0 to 5,000. Four red dots mark the high, upper-middle, lower-middle, and low income groups, running from the top left to the bottom right. Panel a shades air conditioning adoption from 0 to 100 per cent, which rises steeply with income and stays near zero across the whole lower half of the plot. Panel b shades the Cooling Deficit Index from 0 to 5,000 degree-days, which is lowest at the high-income dot and highest at the low-income dot.
Air conditioning adoption is governed by income far more than by heat (panel a), so the Cooling Deficit Index — hot days endured without cooling — is worst exactly where incomes are lowest and cooling degree days are highest (panel b). The four income groups sit along the diagonal of that trade-off. Figure 3 from Wongel et al. (2025), Environmental Research Letters 20, 124045. Reproduced under CC BY 4.0. Extracted from the published PDF and resized for web display.

What question did this research address?

Warming increases the number of dangerously hot days. Economic growth increases the fraction of people who own air conditioning. The two run in opposite directions, so whether heat exposure gets better or worse in a given country is genuinely ambiguous.

This paper asked which effect wins, country by country, and what rate of economic growth would be needed for development to outpace warming.

What did we find?

The paper defines a Cooling Deficit Index as the product of cooling degree days and the fraction of the population without air conditioning, giving a single measure of how much high temperature is actually endured without relief.

The index is used to trace the relationship between global warming, economic growth, and the share of population exposed to high temperatures without the benefit of cooling.

Lower-income countries score worst on both counts. They have the most high-temperature days without cooling now, and they are projected to see the largest increases as temperatures rise.

The growth required to offset that is the central quantitative result. These countries would need GDP growth rates exceeding their own historical rates simply to prevent the number of uncooled hot days from increasing.

Why does it matter?

The finding sharpens what adaptation through development actually demands. Air conditioning is a real and effective adaptation, but the analysis shows growth at historically normal rates does not deliver it fast enough in the places that need it most.

The index itself is a contribution beyond the result. Cooling degree days alone describe the climate, and air-conditioning penetration alone describes the economy; their product describes the exposure that actually matters to people, and it can be computed anywhere.

Citation

Alicia Wongel, Lyssa M. Freese, Edgar Virgüez, Steven J. Davis, and Ken Caldeira (2025). Economic development, air conditioning and adaptation to warming. Environmental Research Letters 20, 124045.

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