by Bill Gates
Still, the idea took hold. The next big air-conditioning advance was made in 1902 by an engineer named Willis Carrier, when his employer sent him to a print shop in New York to figure out how to keep the pages of magazines from wrinkling as they came off the printing press. Realizing that the wrinkles were caused by high humidity levels, Carrier designed a machine that lowered the humidity while also decreasing the temperature in the room. He didn’t know it yet, but he had given birth to the air-conditioning industry.
Barely more than a century after the first A/C unit was installed in a private residence, 90 percent of American households now have some type of air conditioner. If you’ve ever enjoyed a game or concert in a domed stadium, you can thank air-conditioning. And it’s hard to imagine that places like Florida and Arizona would be attractive destinations for retirees today without it.
Air-conditioning is no longer simply a pleasant luxury that makes summer days bearable; the modern economy depends on it. To take just one example: The server farms containing thousands of computers that make today’s computing advances possible (including the ones that run the cloud services where you store music and photos) generate huge amounts of heat. If they didn’t stay cool, the servers would melt down.
If you live in a typical American home, your air conditioner is the biggest consumer of electricity you own—more than your lights, refrigerator, and computer combined.* I counted electricity emissions in chapter 4, but I’m mentioning them again here because space cooling is such a key contributor now and in the future. Also, although A/C units demand the most electricity, they’re not the largest consumers of energy in American homes and businesses. That honor goes to our furnaces and water heaters. (This is also true in Europe and many other regions.) I’ll get to heating air and water in the next section.
Americans are not alone in liking—and needing—cool air. Worldwide, there are 1.6 billion A/C units in use, but they’re not evenly distributed. In rich countries like the United States, 90 percent or more of households have air-conditioning, while in the hottest countries in the world less than 10 percent do.
A/C is on the way. In some countries, most houses have air-conditioning, but in others it is much less common. In the coming decades, the countries at the bottom of this chart will be getting both hotter and richer, which means they’ll be buying and running more A/C units. (IEA)
That means we’ll be adding many more units as the population grows and gets richer and as heat waves become more severe and more frequent. China added 350 million units between 2007 and 2017 and is now the largest market in the world for air conditioners. Worldwide, sales rose 15 percent in 2018 alone, with much of the growth coming from four countries where temperatures get especially high: Brazil, India, Indonesia, and Mexico. By 2050, there will be more than 5 billion A/C units in operation around the world.
Ironically, the very thing we’ll be doing to survive in a warmer climate—running air conditioners—could make climate change worse. After all, air conditioners run on electricity, so as we install more of them, we’ll need more electricity to run them. In fact, the International Energy Agency projects that worldwide electricity demand for cooling will triple by 2050. At that point, air conditioners will consume as much electricity as all of China and India do now.
That will be good for people who suffer in heat waves, but bad for the climate, because in most parts of the world generating power is still a carbon-intensive process. That’s why all the electricity used by buildings—for air-conditioning as well as lights, computers, and so on—is responsible for nearly 14 percent of all greenhouse gases.
The fact that air-conditioning relies so much on electricity makes it easy to calculate the Green Premium for cool air. To decarbonize our air conditioners, we need to decarbonize our power grids. This is another reason why we need breakthroughs in generating and storing electricity like the ones I described in chapter 4; otherwise, emissions will keep going up, and we’ll be stuck in a vicious cycle, making our homes and offices progressively cooler while making the climate progressively hotter.
Fortunately, we don’t have to wait for those breakthroughs. We can take action now to reduce the amount of electricity needed for air conditioners, and therefore lower the emissions caused by staying cool. And there’s no technical barrier to doing this. Most people simply don’t buy the most energy-conscious air conditioners on the market. According to the IEA, the typical A/C unit sold today is only half as efficient as what’s widely available and only a third as efficient as the best models.
Mostly that’s because consumers can’t get all the information they need when they’re picking an air conditioner. For example, a less efficient unit might be cheaper to buy but more expensive to own in the long run, because it uses more electricity. Yet if the units aren’t labeled clearly, you might not have any way to know that when you’re shopping around. (Such labels are required in the United States but not globally.) Plus, many countries don’t set minimum standards for the efficiency of air conditioners. The IEA found that simply by creating policies to fix problems like these, the world can double the average efficiency of A/C units and reduce the growth of energy demand for cooling at mid-century by 45 percent.
Unfortunately, their demand for electricity isn’t the only thing that makes air conditioners a problem. They also contain refrigerants—known as F-gases, because they contain fluorine—that leak out little by little over time when the unit ages and breaks down, as you’ve no doubt noticed if you’ve ever had to replace the coolant in your car’s air conditioner. F-gases are extremely powerful contributors to climate change: Over the course of a century, they cause thousands of times more warming than an equivalent amount of carbon dioxide. If you don’t hear much about them, it’s because they’re not a huge percentage of greenhouse gases; in the United States, they represent about 3 percent of emissions.
Yet F-gases haven’t gone unnoticed. In 2016, representatives from 197 countries committed to reducing the production and use of certain F-gases by more than 80 percent by 2045—a commitment they could make because various companies are developing new approaches to air-conditioning that replace F-gases with less harmful coolants. These ideas are in the early stages of development, far too early to put a price tag on them, but they’re good examples of the kind of innovation we’ll need to keep cool without making the world any warmer.
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In a book about global warming, it may seem strange to discuss staying warm. Why turn up the thermostat when it’s already hot outside? For one thing, when we talk about heat, we’re not just talking about making the air warmer; we also have to heat water for everything from showers and dishwashers to industrial processes. But more to the point, winter isn’t going away. Even as global temperatures go up overall, it’s still going to freeze and snow in many places around the world. And winters are especially hard for anyone who relies on renewables. In Germany, for example, during the winter the amount of solar power available can drop by as much as a factor of nine, and there are also periods with no wind. But you still need electricity; without it, people will freeze to death in their own homes.
Together, furnaces and water heaters account for a third of all emissions that come from the world’s buildings. And unlike lights and A/C units, most of them run on fossil fuels, not electricity. (Whether you use natural gas, heating oil, or propane depends largely on where you live.) This means we can’t decarbonize hot water and air simply by cleaning up our electric grid. We need to get heat from something other than oil and gas.
The path to zero carbon for heating actually looks a lot like the path for passenger cars: (1) electrify what we can, getting rid of natural gas water heaters and furnaces, and (2) develop clean fuels to do everything else.
The good news is that step 1 can actually carry a negative Green Premium. Unlike electric cars, which are more expensive to own than their gas-powered counterparts, all-electric heating and cooling lets you save money. And th
at’s true whether you’re building new construction from scratch or retrofitting an older home. In most locations, your overall costs will go down if you get rid of an electric air conditioner and gas (or oil) furnace and replace both with an electric heat pump.
The idea of a heat pump can seem odd the first time you hear it. Although it’s easy to imagine pumping water or air, how on earth would you pump heat?
Heat pumps take advantage of the fact that gases and liquids change temperature as they expand and contract. The pumps work by moving some coolant through a closed loop of pipes, using a compressor and special valves to change the pressure along the way so that the coolant absorbs heat from one place and gets rid of it somewhere else. In the winter, you move heat from outdoors into your home (this is possible in all but the very coldest climates); in the summer, you do the opposite, pumping heat from inside your house to the outdoors.
This isn’t as mysterious as it may sound. You already have a heat pump in your home, and it’s probably operating right now. It’s called a refrigerator. The warm air that you feel blowing from the bottom of your fridge is what carries the heat away from your food and keeps it cool.
How much money can a heat pump save you? It varies from city to city, depending on how harsh the winter is, how much electricity and natural gas cost, and other factors. Here are a few examples of the savings on new construction in cities around the United States, including the cost of installing a heat pump and operating it for 15 years:
Green Premiums for installing an air-sourced heat pump in selected U.S. cities
City
Cost of natural gas & electric A/C
Cost of air-sourced heat pump
Green premium
Providence, RI
$12,667
$9,912
-22%
Chicago, IL
$12,583
$10,527
-16%
Houston, TX
$11,075
$8,074
-27%
Oakland, CA
$10,660
$8,240
-23%
You won’t save as much if you’re retrofitting an existing home, but switching to a heat pump is still less expensive in most cities. In Houston, for example, doing this will save you 17 percent. In Chicago, your costs will actually go up 6 percent, because natural gas there is unusually cheap. And in some older homes it’s simply not practical to find space for new equipment, so you might not be able to upgrade at all.
Still, these negative Green Premiums raise an obvious question: If heat pumps are such a great deal, why are they in only 11 percent of American homes?
Partly it’s because we replace our furnaces only every decade or so, and most people don’t have enough extra cash on hand to simply replace a perfectly good furnace with a heat pump.
But there’s another explanation as well: outdated government policies. Since the energy crisis of the 1970s, we’ve been trying to cut down on energy use, and so state governments created various incentives to favor natural gas furnaces and water heaters over less efficient electric ones. Some modified their building codes to make it harder for homeowners to replace their gas appliances with electric alternatives. Many of these policies that prize efficiency over emissions are still on the books, restricting your ability to lower your emissions by swapping out a gas-burning furnace for an electric heat pump—even if doing this would save you money.
This is frustrating in that familiar “regulations really can be dumb” way. But if you look at it from a different angle, it’s good news. It means we don’t need some additional technological breakthrough to reduce our emissions in this area, beyond decarbonizing our power grid. The electric option already exists, it’s widely available, and it isn’t merely price competitive—it’s actually cheaper. We just need to make sure our government policies keep up with the times.
Unfortunately, although it’s technically possible to zero out heating emissions by going electric, it won’t happen quickly. Even if we fixed the self-defeating regulations I mentioned, it’s not realistic to think we’ll simply rip out all our gas furnaces and water heaters and replace them with electric ones overnight, any more than we’re suddenly going to run the world’s fleet of passenger cars on electricity. Given how long today’s furnaces last, if we had a goal of getting rid of all the gas-powered ones by mid-century, we’d have to stop selling them by 2035. Today around half of all furnaces sold in the United States run on gas; worldwide, fossil fuels provide six times more energy for heating than electricity does.
To me, that’s another argument for why we need advanced biofuels and electrofuels like the ones I mentioned in chapter 7—ones that can be run in the furnaces and water heaters we have today, without modification, and that don’t add more carbon to the atmosphere. But right now, both options carry a hefty Green Premium:
Green Premiums to replace current heating fuels with zero-carbon alternatives
Fuel type
Current retail price
Zero-carbon option
Green premium
Heating oil
(per gallon)
$2.71
$5.50
(advanced biofuels)
103%
Heating oil
(per gallon)
$2.71
$9.05
(electrofuels)
234%
Natural gas
(per therm)
$1.01
$2.45
(advanced biofuels)
142%
Natural gas
(per therm)
$1.01
$5.30
(electrofuels)
425%
NOTE: Retail price per gallon is the average in the United States from 2015 to 2018. Zero-carbon is current estimated price.
Let’s look at what these premiums would mean for a typical U.S. family. If they heat their home with fuel oil, they’re going to pay $1,300 more if they want to use advanced biofuels, and more than $3,200 extra if they choose electrofuels. If their home is heated with natural gas, switching to advanced biofuels would add $840 to their bill each winter. Switching to electrofuels would add nearly $2,600 each winter.
Clearly we need to drive down the price of these alternative fuels, as I argued in chapter 7. And there are other steps we can take to decarbonize our heating systems:
Electrify as much as we can, getting rid of gas-powered furnaces and water heaters and replacing them with electric heat pumps. In some regions, governments will have to update their policies to allow—and encourage—these upgrades.
Decarbonize the power grid by deploying today’s clean sources where they make sense and investing in breakthroughs for generating, storing, and transmitting power.
Use energy more efficiently. This may seem like a contradiction, because just a few paragraphs ago I complained about policies that prize higher efficiency over lower emissions. The truth is, we need both.
The world is undergoing a huge construction boom. To accommodate a growing urban population, we’ll add 2.5 trillion square feet of buildings by 2060—the equivalent, as I mentioned in chapter 2, of putting up another New York City every month for 40 years. It’s a fair bet that many of these buildings will not be designed to conserve energy and that they’ll be around, using energy inefficiently, for several decades.
The good news is that we know how to build green buildings—as long as we’re willing to pay a Green Premium. An extreme example is Seattle’s Bullitt Center, which lays claim to being one of the greenest commercial buildings in the world. The Bullitt Center was designed to naturally stay warm in the winter and cool in the summer, reducing the need for heating and air-conditioning, and features other energy-saving technologies such as a superefficient elevator. At times, it can generate 60 percent more energy than it consumes, thanks to solar panels on its roof, although it’s still plugged into the city’s electric grid and draws power at night and during especially cloudy stret
ches. Which we have plenty of here in Seattle.
Although many of the Bullitt Center’s technologies are currently too expensive for widespread use (which is why it remains one of the world’s greenest buildings seven years after it opened), we can still make homes and offices more efficient at a low cost. They can be designed with what developers call a supertight envelope (not much air leaking in or out), good insulation, triple-glazed windows, and efficient doors. I’m also intrigued by windows that use so-called smart glass, which automatically turns darker when the room needs to be cooler and lighter when it needs to be warmer. New building regulations can help promote these energy-saving ideas, which will expand the market and drive down their cost. We can make a lot of buildings more energy efficient, even if they can’t all be as efficient as the Bullitt Center.
The Bullitt Center in Seattle is one of the greenest commercial buildings in the world.
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We’ve now covered all five major sources of greenhouse gas emissions: how we plug in, make things, grow things, get around, and keep cool and warm. I hope three things are clear by now:
The problem is extremely complex, touching on almost every human activity.
We have some tools at hand that we should be deploying now to reduce emissions.
But we don’t have all the tools we need. We need to drive down the Green Premiums in every sector, which means we’ve got a lot of inventing to do.
