Air conditioners aren't ready for a hotter, more humid planet

"It's not the heat, it's the humidity."

That's what people say in the summer, when stepping outside feels like being enveloped in a thick, puréed soup. When sweat — the body's natural cooling mechanism — can't evaporate off the body and pools on the skin. For humans, the saying is true: It's humidity that can take simply "hot" temperatures and tip them over the edge into "unsurvivable."

But it also applies to humanity's lifeline on a warming planet: air conditioners.

It's well known that many air conditioners are energy guzzlers that are filled with planet-warming refrigerants. Air conditioning generates about 4 percent of global greenhouse gas emissions, twice as much as the entire aviation industry. But what many people don't realize is that most air conditioners put an enormous amount of their energy just toward removing humidity from the air.

Removing that humidity is critical for human health and comfort. But a group of experts is warning that the current generation of air conditioners isn't ready for the hot and humid future.

Modern air conditioners do two things: They cool the air and, in turn, they also reduce humidity. (Cooler air holds less water vapor, so a change in air temperature means that some water vapor will have to be condensed into water.) But most air conditioners today have been designed to do the former, not the latter; they aren't necessarily equipped or tested for very humid areas.

In humid conditions, humans feel hotter — even at the same temperature. That's why experts measuring heat stress like to use "wet-bulb temperature," a measure of heat and humidity combined. Seventy degrees Fahrenheit with 40 percent humidity might feel relatively comfortable, while 70 degrees and 70 percent humidity would feel uncomfortably hot.

People tend to set their air conditioners to lower temperatures on humid days to compensate for the sticky discomfort. That, in turn, uses a ton of energy. "Air conditioners tend to overcool in order to remove humidity from the air," said Nihar Shah, director of the Global Cooling Efficiency Program at Lawrence Berkeley National Laboratory. "The air conditioners consume more energy than they need to."

According to a study from researchers at the National Renewable Energy Laboratory, more than half of the emissions of air conditioning comes from units removing humidity from the air. As the researchers noted: "Managing humidity with air conditioners contributes more to climate change than controlling temperature."

And as temperatures warm, humid regions of the world are expected to invest heavily in air conditioning. According to the International Energy Agency, approximately 10 air conditioners will be sold every second between now and 2050. India and China combined are expected to buy billions of air conditioners over the next few decades, as residents struggle to protect themselves from rising heat.

But today's ACs aren't tested for super-humid conditions. Around the world, air conditioners are tested with an outdoor temperature of 95 degrees Fahrenheit and a constant speed set on the compressor (essentially the engine of the air conditioner). That doesn't account for high-humidity conditions, or some of the high temperatures seen in countries like India. So these new adopters in high-heat and high-humidity environments are likely to use more energy and pay higher electricity costs than necessary.

More efficient and effective air conditioners do exist. Next-generation technology can cool homes with dramatically lower electricity use, and can even remove humidity from the air more effectively using things like drying agents.

But to get those newer appliances on the market, international organizations and countries are going to have to update their standards to ensure that the next 2 billion air conditioners aren't huge energy hogs. Adoption of billions more typical, inefficient appliances could result in an extra 100 billion metric tons of greenhouse gas emissions by 2050 — equivalent to two years of the world's entire carbon output.

Several groups, including the clean energy think tank RMI, the Lawrence Berkeley National Laboratory and CEPT University in India, are calling for an update to those standards and new ways of testing air conditioners that account for humid air. Air conditioners, they argue, should be tested as they are used — at different temperatures and humidity levels with different compressor speeds, so consumers know the best options available to them.

"Demand for cooling is going to explode," said Ankit Kalanki, a manager for carbon-free buildings at RMI. "If it happens the way technology and standards exist today, we’re going to add a lot of emissions."

Understanding our climate: Global warming is a real phenomenon, and weather disasters are undeniably linked to it. As temperatures rise, heat waves are more often sweeping the globe — and parts of the world are becoming too hot to survive.

What can be done? The Post is tracking a variety of climate solutions, as well as the Biden administration's actions on environmental issues. It can feel overwhelming facing the impacts of climate change, but there are ways to cope with climate anxiety.

Inventive solutions: Some people have built off-the-grid homes from trash to stand up to a changing climate. As seas rise, others are exploring how to harness marine energy.

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