How to Avoid a Climate Disaster

by Bill Gates

  Greenhouse gas emissions have increased dramatically since the 1850s due to human activity, such as burning fossil fuels. Check out the charts on this page. On the left you can see how much our carbon dioxide emissions have grown since 1850, and on the right you can see how much the average global temperature has gone up.

  How do greenhouse gases cause warming? The short answer: They absorb heat and trap it in the atmosphere. They work the same way a greenhouse works—hence the name.

  You’ve actually seen the greenhouse effect in action on a very different scale, whenever your car is sitting outside in the sun: Your windshield lets sunlight in, then traps some of that energy. That’s why the interior of your car can get so much hotter than the outside temperature.

  But that explanation only raises more questions. How can the sun’s heat get past greenhouse gases on its way to the earth but then get trapped by these same gases in our atmosphere? Does carbon dioxide work like some giant one-way mirror? For that matter, if carbon dioxide and methane trap heat, why doesn’t oxygen?

  The answers lie in a neat bit of chemistry and physics. As you may recall from physics class, all molecules vibrate; the faster they vibrate, the hotter they are. When certain types of molecules are hit with radiation at certain wavelengths, they block the radiation, soak up its energy, and vibrate faster.

  But not all radiation is on the right wavelengths to cause this effect. Sunlight, for example, passes right through most greenhouse gases without getting absorbed. Most of it reaches the earth and warms up the planet, just as it has been doing for eons.

  Here’s the problem: The earth doesn’t hold on to all that energy forever; if it did, the planet would already be unbearably hot. Instead, it radiates some of the energy back toward space, and some of this energy is emitted in just the right range of wavelengths to get absorbed by greenhouse gases. Rather than going out harmlessly into the void, it hits the greenhouse molecules and makes them vibrate faster, heating up the atmosphere. (By the way, we should be thankful for the greenhouse effect; without it, the planet would be far too cold for us. The problem is that all these extra greenhouse gases are sending the effect into overdrive.)

  Why don’t all gases act this way? Because molecules with two copies of the same atom—for example, nitrogen or oxygen molecules—let radiation pass straight through them. Only molecules made up of different atoms, the way carbon dioxide and methane are, have the right structure to absorb radiation and start heating up.

  So that’s the first part of the answer to the question “Why do we have to get to zero?”—because every bit of carbon we put into the atmosphere adds to the greenhouse effect. There’s no getting around physics.

  Carbon dioxide emissions are on the rise, and so is the global temperature. On the left you see how our carbon dioxide emissions from industrial processes and burning fossil fuels have gone up since 1850. On the right you see how the global average temperature is rising along with emissions. (Global Carbon Budget 2019; Berkeley Earth)

  The next part of the answer involves the impact that all those greenhouse gases are having on the climate, and on us.

  What We Do and Don’t Know

  Scientists still have a lot to learn about how and why the climate is changing. IPCC reports acknowledge up front some uncertainty about how much and how quickly the temperature will go up, for example, and exactly what effect these higher temperatures will have.

  One problem is that computer models are far from perfect. The climate is mind-blowingly complex, and there’s a lot we don’t understand about things like how clouds affect warming or the impact of all this extra heat on ecosystems. Researchers are identifying these gaps and trying to fill them in.

  Still, there is a lot that scientists do know and can state with confidence about what will happen if we don’t get to zero. Here are a few key points.

  The earth is warming, it’s warming because of human activity, and the impact is bad and will get much worse. We have every reason to believe that at some point the impact will be catastrophic. Will that point come in 30 years? Fifty years? We don’t know precisely. But given how hard the problem will be to solve, even if the worst case is 50 years away, we need to act now.

  We’ve already raised the temperature at least 1 degree Celsius since preindustrial times, and if we don’t reduce emissions, we’ll probably have between 1.5 and 3 degrees Celsius of warming by mid-century, and between 4 and 8 degrees Celsius by the end of the century.

  All this extra heat will cause various changes in the climate. Before I explain what’s coming, I have to give you one caveat: Although we can predict the course of broad trends, like “there will be more hot days” and “sea levels will go up,” we can’t with certainty blame climate change for any particular event. For example, when there’s a heat wave, we can’t say whether it was caused by climate change alone. What we can do, though, is say how much climate change increased the odds of that heat wave happening. For hurricanes, it’s unclear whether warmer oceans are causing a rise in the number of storms, but there is growing evidence that climate change is making storms wetter and increasing the number of intense ones. We also don’t know whether or to what extent these extreme events will interact with each other to produce even more serious effects.

  What else do we know?

  For one thing, there will be more really hot days. I could give you statistics from cities throughout the United States, but I’ll pick Albuquerque, New Mexico, because I have a special connection with the place: It’s where Paul Allen and I founded Microsoft in 1975. (Micro-Soft, to be totally accurate—we wisely dropped the hyphen and lowercased the S a couple of years later.) In the mid-1970s, when we were just getting started, the temperature in Albuquerque went over 90 degrees Fahrenheit about 36 times a year, on average. By mid-century, the city’s thermometers will go over 90 at least twice as often every year. By the end of the century, the city could see as many as 114 days that hot. In other words, they’ll go from one month’s worth of hot days every year to three months’ worth.

  Not everyone will suffer equally from hotter and more humid days. For example, the Seattle area, where Paul and I moved Microsoft in 1979, will probably get off relatively easy. We might reach 90 degrees on as many as 14 days a year later this century, after having an average of just one or two a year in the 1970s. And some places might actually benefit from a warmer climate. In cold regions, for example, fewer people will die of hypothermia and the flu, and they’ll spend less money to heat their homes and businesses.

  But the overall trend points toward trouble from a hotter climate. And all this extra heat has knock-on effects; for instance, it means that storms are getting worse. Scientists are still debating whether storms are happening more often because of the heat, but they appear to be getting more powerful in general. We know that when the average temperature rises, more water evaporates from the earth’s surface into the air. Water vapor is a greenhouse gas, but unlike carbon dioxide or methane, it doesn’t stay in the air for long—eventually, it falls back to the surface as rain or snow. As water vapor condenses into rain, it releases a massive amount of energy, as anyone who has ever experienced a big thunderstorm knows.

  Even the most powerful storm typically lasts only a few days, but its impact can reverberate for years. There’s the loss of life, a tragedy in its own right that can leave survivors both heartbroken and, often, destitute. Hurricanes and floods also destroy buildings, roads, and power lines that took years to build. All of that property can eventually be replaced, of course, but doing so siphons off money and time that could be put into new investments that help the economy grow. You’re always trying to catch up to where you were, instead of getting ahead. One study estimated that Hurricane Maria in 2017 set Puerto Rico’s infrastructure back more than two decades. How long before the next storm comes along and sets it back again? We don’t know.

  Hurricane Maria set Puerto Rico’s power grid and other infrastructure back some two decades, accordi
ng to one study.

  These stronger storms are creating a strange feast-or-famine situation: Even though it’s raining more in some places, other places are experiencing more frequent and more severe droughts. Hotter air can hold more moisture, and as the air gets warmer, it gets thirstier, drinking up more water from the soil. By the end of the century, soils in the southwestern United States will have 10 percent to 20 percent less moisture, and the risk of drought there will go up by at least 20 percent. Droughts will also threaten the Colorado River, which supplies drinking water for nearly 40 million people and irrigation for more than one-seventh of all American crops.

  A hotter climate means there will be more frequent and destructive wildfires. Warm air absorbs moisture from plants and soil, leaving everything more prone to burning. There’s a lot of variation around the world, because conditions change so much from place to place. But California is a dramatic example of what’s going on. Wildfires now occur there five times more often than in the 1970s, largely because the fire season is getting longer and the forests there now contain much more dry wood that’s likely to burn. According to the U.S. government, half of this increase is due to climate change, and by mid-century America could experience more than twice as much destruction from wildfires as it does today. This should be worrisome for anyone who remembers America’s devastating wildfire season of 2020.

  Another effect of the extra heat is that sea levels will go up. This is partly because polar ice is melting, and partly because seawater expands when it gets warmer. (Metal does the same thing, which is why you can loosen a ring that’s stuck on your finger by running it under hot water.) Although the overall rise in the global average sea level—most likely, a few feet by 2100—may not sound like much, the rising tide will affect some places much more than others. Beach areas are in trouble, not surprisingly, but so are cities situated on especially porous land. Miami is already seeing seawater bubble up through storm drains, even when it isn’t raining—that’s called dry-weather flooding—and the situation will not get better. In the IPCC’s moderate scenario, by 2100 the sea level around Miami will rise by nearly two feet. And some parts of the city are settling—sinking, essentially—which might add another foot of water on top of that.

  Rising sea levels will be even worse for the poorest people in the world. Bangladesh, a poor country that’s making good progress on the path out of poverty, is a prime example. It has always been beset by severe weather; it has hundreds of miles of coastline on the Bay of Bengal; most of the country sits in low-lying, flood-prone river deltas; and it gets heavy rainfall every year. But the changing climate is making life there even harder. Thanks to cyclones, storm surges, and river floods, it is now common for 20 to 30 percent of Bangladesh to be underwater, wiping out crops and homes and killing people throughout the country.

  Finally, with the extra heat and the carbon dioxide that’s causing it, plants and animals are being affected. According to research cited by the IPCC, a rise of 2 degrees Celsius would cut the geographic range of vertebrates by 8 percent, plants by 16 percent, and insects by 18 percent.

  For the food we eat, it’s a mixed picture, though mainly a grim one. On the one hand, wheat and many other plants grow faster and need less water when there’s a large amount of carbon in the air. On the other hand, corn is especially sensitive to heat, and it’s the number one crop in the United States, worth more than $50 billion a year. In Iowa alone, more than 13 million acres of land are planted with corn.

  Globally, there’s a wide range of possibilities for how climate change could affect the amount of food we get from each acre of crops. In some northerly regions, yields could go up, but in most places they’ll drop, by anywhere from a few percentage points to as much as 50 percent. Climate change could cut southern Europe’s production of wheat and corn in half by mid-century. In sub-Saharan Africa, farmers could see the growing season shrink by 20 percent and millions of acres of land become substantially drier. In poor communities, where many people already spend more than half of their incomes on food, food prices could rise by 20 percent or more. Extreme droughts in China—whose agricultural system provides wheat, rice, and corn for a fifth of the world’s population—could trigger a regional or even global food crisis.

  Extra heat won’t be good for the animals we eat and get milk from; it will make them less productive and more prone to dying young, which in turn will make meat, eggs, and dairy more expensive. Communities that rely on seafood will have trouble too, because not only are the seas getting warmer, they’re also bifurcating—developing some places where the water has more oxygen and others where it has less oxygen. As a result, fish and other sea life are moving to different waters, or simply dying off. If the temperature rises by 2 degrees Celsius, coral reefs could vanish completely, destroying a major source of seafood for more than a billion people.

  When It Doesn’t Rain, It Pours

  You might think that the difference between 1.5 and 2 degrees would not be that great, but climate scientists have run simulations of both scenarios, and the news is not good. In many ways, a 2-degree rise wouldn’t simply be 33 percent worse than 1.5; it could be 100 percent worse. Twice as many people would have trouble getting clean water. Corn production in the tropics would go down twice as much.

  Any one of these effects of climate change will be bad enough. But no one’s going to suffer from just hot days, or just floods, and nothing else. That’s not how climate works. The effects of climate change add up, one on top of the other.

  As it gets hotter, for example, mosquitoes will start living in new places (they like it humid, and they’ll move from areas that dry out to ones that become more humid), so we’ll see cases of malaria and other insect-borne diseases where they’ve never appeared before.

  Heatstroke will be another major problem, and it’s linked to the humidity, of all things. Air can contain only a certain amount of water vapor, and at some point it hits a ceiling, becoming so saturated that it can’t absorb any more moisture. Why does that matter? Because the human body’s ability to cool off depends on the air’s ability to absorb sweat as it evaporates. If the air can’t absorb your sweat, then it can’t cool you off, no matter how much you perspire. There’s simply nowhere for your perspiration to go. Your body temperature stays high, and if nothing changes, you die of heatstroke within hours.

  Heatstroke, of course, is nothing new. But as the atmosphere gets hotter and more humid, it will become a much bigger problem. In the regions that are most in jeopardy—the Persian Gulf, South Asia, and parts of China—there will be times of the year when hundreds of millions of people will be at risk of dying.

  To see what happens when these effects start piling up, let’s look at the impact on individual people. Imagine you’re a prosperous young farmer raising corn, soybeans, and cattle in Nebraska in 2050. How might climate change affect you and your family?

  You’re in the middle of the United States, far from the coasts, so rising sea levels don’t directly harm you. But the heat does. In the 2010s, when you were a kid, you might’ve seen 33 days a year when the temperature hit 90; now it happens 65 or 70 times a year. The rain is also a lot less reliable: When you were a kid, you could expect around 25 inches a year; now it might be as little as 22 or as much as 29.

  Maybe you’ve adjusted your business to the hotter days and the unpredictable rain. Years ago, you invested in new crop varieties that can tolerate extra heat, and you’ve found work-arounds that let you stay inside during the worst part of the day. You didn’t love spending extra money on these crops and work-arounds, but they’re better than the alternative.

  One day, a powerful storm strikes without warning. As nearby rivers spill over the levees that have held them back for decades, your farm gets flooded. It’s the kind of deluge your parents would’ve called a hundred-year flood, but now you’d consider yourself lucky if it happened only once a decade. The waters wash away large portions of your corn and soybean crops, and your stored grain
is soaked so thoroughly that it rots and you have to throw it away. In theory, you could sell your cattle to make up for the loss, but all your cattle feed has been swept away too, so you won’t be able to keep them alive for long.

  Eventually the waters recede, and you can see that the nearby roads, bridges, and rail lines are now unusable. Not only does that keep you from shipping out whatever grain you’ve managed to preserve; it also makes it harder for trucks to deliver the seeds you need for the next planting season, assuming your fields are still usable. It all adds up to a disaster that could end your farming career and force you to sell off land that has been in your family for generations.

  It may sound as if I’m cherry-picking the most extreme example, but things like this are already happening, especially to poor farmers, and in a few decades they could be happening to far more people. And as bad as it sounds, if you take a global perspective, you’ll see that things will be much worse for the poorest 1 billion people in the world—people who are already struggling to get by and who will only struggle more as the climate gets worse.

  Now imagine you live in rural India, where you and your husband are subsistence farmers, which means you and your kids eat nearly all the food you raise. In an especially good season, you sometimes have enough left over to sell so you can buy medicine for your kids or send them to school. Unfortunately, heat waves have become so common that your village is becoming unlivable—it’s not at all unusual to have several days in a row over 120 degrees—and between the heat and the pests that are now invading your fields for the first time, it’s almost impossible to keep your crops alive. Although monsoons have flooded other parts of the country, your community has received far less rain than normal, making it so hard to find water that you survive off a trickling pipe that runs only a few times a week. It’s getting even tougher to simply keep your family fed.