Want air conditioning and a healthier planet? Here’s one step we can take today.
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The heat wave has broken, yet you’d never know it when you step into your apartment. It may be a pleasant 75 degrees outdoors, but inside it’s well into the 90s.

Ever wondered why this is? There’s a simple explanation. Buildings in predominantly cold climates – like Boston and northern Europe - were historically designed to retain heat. They were built using building materials like brick and concrete – materials that have what is called a high thermal mass.

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For centuries this was all well and good. But with the onset of climate change, these heat conserving buildings have come to pose hazards. Materials with a high thermal mass have a strong ability to absorb and store heat during the day. And, under typical weather conditions when the air cools at night, these materials then re-radiate that heat, and the process starts anew. But what happens if nighttime temperatures don’t drop, as happens during a heat wave?

In that scenario, these materials don’t have a chance to shed the excess heat, so it stays stored in the building, like a battery ready to discharge. So even when outdoor temperatures drop, those materials with all their stored heat start to wreak havoc. The outdoor heat wave ends, but the indoor heat wave continues.

We see the impact on public health in the statistics: more than 14,000 deaths in Paris during a heat wave in 2003, 700 deaths per day in Moscow in 2010 (heat wave and pollution from wildfires), and 70 deaths in Quebec earlier this month. Many of these deaths occur in those over 55 years old, in areas that were traditionally colder climates, and cities that have a higher percentage of buildings without air conditioning than their more southerly counterparts in the Northern Hemisphere.

Moreover, vulnerable populations are far from only ones affected. In a recently published study, we asked healthy college-aged students to perform a variety of tasks before and during a heat wave. Half of these students had rooms with air-conditioning, and half did not.

We found that those students without AC had 13 percent longer reaction times on color-word tests, 11 percent longer reaction time on basic arithmetic tests, and 10 percent reduction in the number of correct responses per minute (what we call ‘throughput’). Taken together, our study showed that those with AC had not just faster responses, but also more accurate responses.

These findings fit with other recent research on the impacts of temperature on cognitive function. Last year, our study on healthy office workers found 5 percent lower cognitive function test scores when their office temperature fell outside of what is typically defined as ‘comfortable’. New research examining standardized test scores from 10 million American high school students showed that a 1°F increase in school year temperature reduces that year's learning by 1 percent and the impact is triple among the poorest schools. Access to AC in schools seem to offset these effects.

Heat waves are a massive public health issue – not just for the old, sick, and very young but for everyone. Air conditioners are fast becoming a necessity around the world. Lawrence Berkeley National Laboratory predicts that we will need 700 million new air-conditioners by 2030, and a mind-blowing 1.3 billion by 2050.

What to do, then, about the environmental impacts of this technology? Amidst all the hand-wringing, there is one significant step that we can act on today: The elimination of hydrofluorocarbon refrigerants in these air-conditioners.

HFCs, as they are called, are a potent greenhouse gas – up to 3,000 times more potent than carbon dioxide. If we eliminate HFC use in ACs, we could avoid 0.5°C of global warming by the end of this century. For perspective, the Paris Agreement signed by countries around the world to begin to address climate change, is designed to keep global warming below 2.0°C  (The U.S., under President TrumpDonald John TrumpTrump to fundraise for 3 Republicans running for open seats: report Trump to nominate former Monsanto exec to top Interior position White House aides hadn’t heard of Trump's new tax cut: report MORE, has signaled its intent to withdraw at the earlier possible date, in 2020.)

HFCs were a regrettable substitute to ozone-depleting refrigerants that were banned as part of the Montreal Protocol in 1987. In 2016, the Kigali Amendment to the Montreal Protocol was put forward, which aims to address the HFC problem, calling for an 80 percent reduction in global HFC use by 2030. 197 countries have since ratified the amendment. The good news is that alternatives to HFCs are available.

Even better news – every major air-conditioner company in the U.S., as well as the Chamber of Commerce, have voiced strong support for the Kigali Amendment. Why? It makes business sense. Alternatives to HFCs are ready to go to market. The trade group for AC companies estimates that ratifying the deal would lead to 33,000 jobs and $12.5 billion in annual economic output. The icing on the cake? The Kigali Amendment has widespread bipartisan support.

If that’s the case, what is the status of the Kigali Amendment in the U.S. now, you ask? The answer is that it’s sitting on the desk of President Trump, waiting to be sent to the Senate for ratification.

U.S. manufacturers want it. Businesses want it. Legislators from both sides of the aisle want it. And our health depends on it. What’s delaying President Trump?

Joseph Allen, Assistant Professor, Harvard T.H. Chan School of Public Health; Co-Director, Harvard Center for Climate, Health and the Global Environment, @j_g_allen. Jose Guillermo Cedeno Laurent, Research Fellow, Harvard T.H. Chan School of Public Health, @cedenolaurent