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Air conditioning is adding to the climate crisis. But it doesn’t need to be

Heat maps of cities, including Boston, show deep inequality in access to cooling.

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June 2021 was the hottest June recorded in US history, and July was the hottest month on Earth in recorded history. In August, the Intergovernmental Panel on Climate Change published its latest report, concluding that it is “unequivocal” that the effects we already see are caused by humans, that many of the changes are “irreversible,” and that the relationship between emissions and extreme weather events is “established fact.” It states that on our present trajectory, by the early 2030s we will reach 1.5 degrees Celsius of warming — the preferred target limit set by the Paris Agreement — but that if we halt emissions now, we can halt warming.

The UN secretary-general called the report a “code red for humanity.” To reduce emissions, we need to immediately end the coal age (coal is one of the biggest pollutants), reduce other carbon dioxide emissions, and aggressively attack methane emissions (they act as a supercharger of climate impacts). Every country and company must be on a science-based transition pathway to arrive at a 1.5-degree Celsius world. That requires removing subsidies from fossil fuels and mobilizing trillions of dollars of investment needed to protect nature and to produce clean, affordable energy.


All of that must be done without leaving people behind. We are already living in a world scarred by climate change — the fires, floods, rising sea levels, extreme rainfall and drought, loss of crops and forests (our planet’s lungs), and deaths and illnesses from extreme heat. We must invest to build our resilience to the forces we have unleashed.

Yet, as we’ve learned from the COVID-19 pandemic, our resilience is dependent on that of our neighbors and communities. In extreme heat, no matter our socioeconomic status, we need health facilities to be air conditioned and safe; fresh food and medicine — especially vaccines amid a pandemic — to be safely stored and transported within a cold chain that often spans the world; and our homes, schools, and workplaces to be cool enough so we can work efficiently and sleep soundly.


As extreme, often humid, heat forms with greater regularity, we face a dangerous irony: the demand for cooling goes up, yet cooling as we’ve known it makes a sizable contribution to the climate crisis through its energy demands and use of super-pollutants. The coolants that make it work, hydrofluorocarbons, are a type of greenhouse gas even more damaging to the climate than carbon dioxide.

But there is a virtuous circle at hand, with concerted action we can take locally and globally. First, let’s shift the way we think about heating and cooling. For example, we must systematically recover the waste heat from cooling, such as the hot air in the alley behind the neighborhood convenience store or supermarket. It contributes to the heat island effect, where heat is trapped in our urban, built environments.

Then, international cooperation can help. We need to get super-polluting hydrofluorocarbons out of refrigeration and air conditioning. A lot hinges on the success in implementing the 2016 Kigali Amendment to the Montreal Protocol, which would phase out HFCs. The United States signaled earlier this year that action under Kigali is a big part of its climate action push.

Increasing resilience to climate change and becoming greener have a global dimension. US manufacturers are leaders in non-fluorinated refrigerants, and as cooling and refrigeration needs grow, especially overseas, it’s an opportunity for American companies.


Beyond that, our focus must be on passive cooling. In a report published by the World Bank, Primer for Cool Cities, emphasis is on reflective roofs, walls, and pavements; adding permeable surfaces to buildings — green roofs and walls — and permeable pavements; and adding more parks and tree canopies. Combine that approach with urban design solutions that maximize natural wind flow and don’t trap as much heat, and cities could stay cooler outside and inside.

Heat maps of cities, including Boston, show deep inequality in access to cooling. For many, gaining access will require new technologies and business models that work on off-grid renewable energy systems. The market for low-cost, nonpolluting, super-efficient refrigeration and cooling is large and growing. For a sense of the innovation potential, just look at the finalists and winners of the Global Cooling Prize and the partnerships emerging from the Chill Challenge. The Million Cool Roofs Challenge and the Fair Cooling Fund offered financial support to communities in developing countries.

Inspiration comes from urban forests in Melbourne, mobile green living rooms in Frankfurt, and white roofs for low-income families in Ahmedabad, India. Closer to home, microgrids in communities like Chelsea will provide reliable, clean energy for cooling that can combine with passive cooling solutions like greening and cool roofs for greater impact.

This summer, many of us became aware of the “wet bulb” number. As the measurement that combines temperature and humidity into one value, it represents the point at which water stops evaporating from a wet thermometer bulb. For humans, this is the point at which sweat, our cooling mechanism, can no longer cool us. When the wet-bulb temperature reaches 95 degrees Fahrenheit, it crosses a threshold at which humans can no longer lose internal body heat (serious health consequences can arise at even lower than 95 degrees).


Climate scientists have been warning us for more than 40 years of the dangers of our carbon-intensive economic models. Now, they’ve said, with incredible unanimity and clarity, that we have a last chance to change, and that if we do, we can slow and then halt the damage we are causing.

As we realize how important it is to be cool, we must act and act now. One small contribution would be for meteorologists to arm us with knowledge by talking about the wet bulb number alongside advisories on heat, pollen, and clean air, making it part of our everyday thinking.

Rachel Kyte is dean of The Fletcher School at Tufts University. She is an adviser to the UN secretary-general on climate and energy issues. Send comments to