[Book Notes] 30 insights on climate change: How to avoid a climate disaster

Bill Gates’s book – How to avoid a climate disaster – is one of the most factual and technical explanation of climate change. The book does a great job in systematically identifying the sources of climate change and communicating the magnitude of changes that we will need to make to avoid a climate disaster. Therefore, this book came very close to the mathematical explanation of climate change and energy technology in David MacKay’s fantastic book, Sustainable Energy – without the hot air (which is available for free at the book’s website). My notes from this book are as follows:

Bill Gates’s video summary of this book is also very informative:


There are two numbers you need to know about climate change. The first is 51 billion. The other is zero. 51 billion is how many tons of greenhouse gases the world typically adds to the atmosphere every year. Although the figure may go up or down a bit from year to year, it’s generally increasing. This is where we are today. Zero is what we need to aim for.



Impact of covid-19 on climate change:

Because economic activity has slowed down so much, the world will emit fewer greenhouse gases this year than last year. As I mentioned earlier, the reduction will probably be around 5 percent. In real terms, that means we will release the equivalent of 48 or 49 billion tons of carbon, instead of 51 billion. That’s a meaningful reduction, and we would be in great shape if we could continue that rate of decrease every year. Unfortunately, we can’t. Consider what it took to achieve this 5 percent reduction. A million people died, and tens of millions were put out of work. To put it mildly, this was not a situation that anyone would want to continue or repeat. And yet the world’s greenhouse gas emissions probably dropped just 5 percent, and possibly less than that.

In the next decade or two, the economic damage caused by climate change will likely be as bad as having a COVID-sized pandemic every 10 years.

Impact of covid on climate change


The world overall should be using more of the goods and services that energy provides. There is nothing wrong with using more energy as long as it’s carbon-free. The key to addressing climate change is to make clean energy just as cheap and reliable as what we get from fossil fuels.

There are no realistic paths to zero that involve abandoning these (i.e. fossil) fuels completely or stopping all the other activities that also produce greenhouse gases (like making cement, using fertilizer, or letting methane leak out of natural gas power plants). Instead, in all likelihood, in a zero-carbon future we will still be producing some emissions, but we’ll have ways to remove the carbon they emit.



Non CO2 greenhouse gases like methane have a bigger impact on climate change.

Molecule for molecule, many of these other gases (like methane) cause more warming than carbon dioxide does—in the case of methane, 120 times more warming the moment it reaches the atmosphere. But methane doesn’t stay around as long as carbon dioxide. Ultimately, what really matters isn’t the amount of greenhouse gas emissions; what matters is the higher temperatures and their impact on humans. And on that front, a gas like methane is much worse than carbon dioxide. It drives the temperature up immediately, and by quite a bit. When you use carbon dioxide equivalents, you aren’t fully accounting for this important short-term effect.



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?

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.

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.



[On the non-traditional impact of climate change]

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.

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.

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.

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.



[on stickiness of fossil fuels]

What’s more, there’s a very good reason why fossil fuels are everywhere: They’re so inexpensive. As in, oil is cheaper than a soft drink. I could hardly believe this the first time I heard it, but it’s true.

Emissions from advanced economies like the United States and Europe have stayed pretty flat or even dropped, but many developing countries are growing fast. That’s partly because richer countries have outsourced emissions-heavy manufacturing to poorer ones.

It takes a really long time to adopt new sources of energy. Notice how in 60 years coal went from 5 percent of the world’s energy supply to nearly 50 percent. But natural gas reached only 20 percent in the same amount of time.

Fuel sources aren’t the only issue. It also takes us a long time to adopt new types of vehicles. The internal combustion engine was introduced in the 1880s. How long before half of all urban families had a car? Thirty to 40 years in the United States, and 70 to 80 years in Europe.



The world uses 5,000 gigawatts of power. The United States uses 1,000 gigawatts. Tip: Whenever you hear “kilowatt,” think “house.” “Gigawatt,” think “city.” A hundred or more gigawatts, think “big country.”



The average retail price for a gallon of jet fuel in the United States over the past few years is $2.22. Advanced biofuels for jets, to the extent they’re available, cost on average $5.35 per gallon. The Green Premium for zero-carbon fuel, then, is the difference between these two prices, which is $3.13. The premiums give us a different insight from the raw number of emissions, which shows us how far we are from zero but tells us nothing about how hard it will be to get there.



[On Direct Air Capture to mitigate climate change]

“How much would it cost to just suck the carbon out of the atmosphere directly?” That idea has a name; it’s called direct air capture. As for the cost of removing a ton of carbon from the air, that figure hasn’t been firmly established, but it’s at least $200 per ton. With some innovation, I think we can realistically expect it to get down to $100 per ton, so that’s the number I’ll use. using the DAC approach to solve the climate problem would cost at least $5.1 trillion per year, every year, as long as we produce emissions. That’s around 6 percent of the world’s economy. (It’s an enormous sum, though this theoretical DAC technology would actually be far cheaper than the cost of trying to reduce emissions by shutting down sectors of the economy, as we’ve done during the COVID-19 pandemic. In the United States, according to data from the Rhodium Group, the per-ton cost to our economy came to between $2,600 and $3,300. In the European Union, it was more than $4,000 per ton. In other words, it cost between 25 and 40 times the $100 per ton we hope to achieve someday.)

How Direct carbon capture works

In reality, the technology behind DAC isn’t ready for global deployment, and even if it were, DAC would be an extremely inefficient method for solving the world’s carbon problem. It’s not clear that we could store hundreds of billions of tons of carbon safely. There’s no practical way to collect $5.1 trillion a year or make sure everyone pays their fair share (and even defining everyone’s fair share would be a major political fight). We’d need to build more than 50,000 DAC plants around the world just to manage the emissions we’re producing right now. In addition, DAC doesn’t work on methane or other greenhouse gases, just carbon dioxide. And it’s probably the most expensive solution; in many cases, it will be cheaper not to emit greenhouse gases in the first place.



On why decarbonization of electric supply is do difficult/expensive [5 stars]

Figuring out how to get all the benefits of cheap, reliable electricity without emitting greenhouse gases is the single most important thing we must do to avoid a climate disaster. That’s partly because producing electricity is a major contributor to climate change, and also because, if we get zero-carbon electricity, we can use it to help decarbonize lots of other activities, like how we get around and how we make things.

Changing America’s entire electricity system to zero-carbon sources would raise average retail rates by between 1.3 and 1.7 cents per kilowatt-hour, roughly 15 percent more than what most people pay now. That adds up to a Green Premium of $18 a month for the average home—pretty affordable for most people, though possibly not for low-income Americans, who already spend a tenth of their income on energy.

It’s not immediately obvious why there’s such a thing as a Green Premium in the first place. Natural gas plants have to keep buying fuel as long as they’re running; solar farms, wind farms, and dams get their fuel for free. Also, there’s the truism that as you take a technology to a broad scale, it gets cheaper. So why does it cost extra to go green? One problem is that fossil fuels are so cheap.

Another reason is that, as I mentioned earlier, some regions of the world simply don’t have decent renewable resources. To get close to 100 percent, we’d have to move lots of clean energy from where it’s made (sunny places, ideally near the equator, and windy regions) to where it’s needed (cloudy, windless ones). That would require building new transmission lines, a costly and time-consuming task—especially if it involves crossing national borders—and the more power lines we install, the more the price of power goes up. In fact, transmission and distribution are responsible for more than a third of the final cost of electricity. And many countries don’t want to rely on other countries for their electricity supply.

But cheap oil and expensive transmission lines aren’t the biggest drivers of the electricity Green Premium. The main culprits are our demand for reliability, and the curse of intermittency.

The clearest example of intermittency is when the sun goes down, cutting off our supply of solar-generated electricity. Suppose we want to solve that problem by taking one kilowatt-hour of excess electricity that’s generated during the day, storing it, and using it that night.

That depends on two factors: how much the battery costs, and how long it’ll last before we have to replace it. For the cost, let’s say we can buy a one-kilowatt-hour battery for $100. (This is a conservative estimate, and I’ll ignore for the moment what happens if we have to take out a loan for this battery.) As for how long our battery will last, let’s assume it can go through 1,000 charge-and-discharge cycles. So the capital cost of this one-kilowatt-hour battery will be $100 spread out over 1,000 cycles, which works out to 10 cents per kilowatt-hour. That’s on top of the cost of generating the power in the first place, which in the case of solar power is something like 5 cents per kilowatt-hour. In other words, the electricity we store for nighttime use will cost us triple what we’re paying during the day—5 cents to generate and 10 cents to store, for a total of 15 cents.

Say we want to store a single kilowatt-hour not for a day but for a whole season. We’ll generate it during the summer and use it in the winter to run a space heater. This time, the battery’s life cycle isn’t an issue, because we’re charging it only once a year. But suppose we have to finance the purchase of the battery. Now we’ve tied up $100 in capital. (Obviously you wouldn’t finance a $100 battery, but you might need financing if you were buying enough to store several gigawatts. And the math is the same.) If we pay 5 percent interest on the capital, and the battery costs $100, that’s an additional $5 cost to store our single kilowatt-hour. And remember how much we’re paying for solar power during the day: just 5 cents. Who would pay $5 to store a nickel’s worth of electricity?

Seasonal intermittency and the high cost of storage cause yet another problem, especially for big users of solar power—the problem of over-generation in the summer and under-generation in the winter. Because the earth is tilted on its axis, the amount of sunlight that hits any given part of the planet varies across the four seasons, as does the intensity of the sunlight.

To see why this variation matters, let’s do another thought experiment. Imagine there’s a town near Seattle—we’ll call it Suntown—that wants to generate a gigawatt of solar power year-round. How big should Suntown’s solar array be? One option would be to install enough panels to produce a gigawatt during the summer, when sunlight is plentiful. But the town would be out of luck in the winter, when it’ll get only half as much sunlight. That’s under-generation. (And the town council is well aware that storage is excessively expensive, so they’ve ruled out batteries.) On the other hand, Suntown could put up all the solar panels it needs for the short, dark days of winter, but then by the time summer arrives, it would be generating way more than necessary. Electricity would be so cheap that the town would be hard-pressed to recoup the expense of installing all those panels. Suntown could deal with this over-generation problem by turning off some of its panels during the summer, but then it’d be sinking money into equipment that gets used only for part of the year. That would raise the cost of electricity even more for every home and business in town; in other words, it would add to the town’s Green Premium.



It’s extremely difficult and expensive to store electricity on a large scale.

Imagine a future where Tokyo gets all its electricity from wind power alone. (Japan does, in fact, have quite a bit of onshore and offshore wind available.) One August, at the peak of cyclone season, a massive storm hits. The winds are so strong that they will rip the city’s wind turbines apart if they aren’t shut down. Tokyo’s leaders decide to switch off the turbines and get by solely on electricity stored up in the best large-scale batteries they can find. Here’s the question: How many batteries would they need in order to power Tokyo for three days, until the storm passes and they can turn the turbines back on? The answer is more than 14 million batteries. That’s more storage capacity than the world produces in a decade. Purchase price: $400 billion. Averaged over the lifetime of the batteries, that’s an annual expense of more than $27 billion. And that’s just the capital cost of the batteries; it doesn’t include other expenses like installation and maintenance.



America’s power grid relies on railroads and pipelines to move fuels over long distances to power plants, and then on transmission lines to move electricity over short distances to the cities that need it.

That model doesn’t work with solar and wind. You can’t ship sunlight in a railcar to some power plant; it has to be converted to electricity on the spot. But most of America’s sunlight supply is in the Southwest, and most of our wind is in the Great Plains, far from many major urban areas.

Just think about how many landowners, utility companies, and local and state governments you’d need to bring together to build power lines that could move solar energy from the Southwest all the way to customers in New England. In other words, we’ll save money by building renewables in the best locations, building a unified national grid, and shipping zero-emissions electrons wherever they’re needed.

As our houses rely less on fossil fuels and more on electricity (for example, to power electric cars and stay warm in the winter), we’ll need to upgrade the electrical service to each household—by at least a factor of two, and in many cases even more than that. A lot of streets will need to be dug up and electrical poles climbed to install heavier wires, transformers, and other equipment. So it will be felt in a real way by nearly every community, and the political impact will get down to the local level.

Technology might be able to help overcome some of the political barriers involved with these upgrades. For example, power lines are less of an eyesore if they’re run underground. But today, burying power lines increases the cost by a factor of 5 to 10. (The problem is heat: Power lines get hot when there’s electricity running through them. That’s no problem when they’re aboveground—the heat just dissipates into the air—but underground there’s no place for the heat to go. If the temperature gets too high, the power lines melt) Some companies are working on next-generation transmission that would eliminate the heat problem and reduce the cost of underground lines significantly.



When you cover land with water, if there’s a lot of carbon in the soil, the carbon eventually turns into methane and escapes into the atmosphere—which is why studies show that depending on where it’s built, a dam can actually be a worse emitter than coal for 50 to 100 years before it makes up for all the methane it’s responsible for.



Here’s the one-sentence case for nuclear power: It’s the only carbon-free energy source that can reliably deliver power day and night, through every season, almost anywhere on earth, that has been proven to work on a large scale.



Alternative forms of energy generation to mitigate climate change:

Fusion: Although it’s still in the experimental phase, fusion holds a lot of promise. Because it would run on commonly available elements like hydrogen, the fuel would be cheap and plentiful. The main type of hydrogen that’s usually used in fusion can be extracted from seawater, and there’s enough of it to meet the world’s energy needs for many thousands of years. Fusion’s waste products would be radioactive for hundreds of years, versus hundreds of thousands for waste plutonium and other elements from fission, and at a much lower level—about as dangerous as radioactive hospital waste. There’s no chain reaction to run out of control, because the fusion ceases as soon as you stop supplying fuel or switch off the device that’s containing the plasma.

Offshore wind: Putting wind turbines in an ocean or other body of water has various advantages. Because many major cities are near the coast, we can generate electricity much closer to the places where it’ll be used and not run into as many transmission problems. Offshore winds generally blow more steadily, so intermittency is less of an issue too. In theory, we could generate 2,000 gigawatts from it—more than enough to meet our current needs. But if we’re going to take advantage of this potential, we’ll have to make it easier to put up turbines. Today, getting a permit requires you to run a bureaucratic gauntlet: You buy one of a limited number of federal leases, then go through a multiyear process to generate an environmental impact statement, then get additional state and local permits. And at each step of the way, you may be opposed (rightly or not) by beachfront property owners, the tourism industry, fishermen, and environmental groups.

Geothermal: Deep underground—as close as a few hundred feet, as far down as a mile—are hot rocks that can be used to generate carbon-free electricity. We can pump water at high pressure down into the rocks, where it absorbs the heat and then comes out another hole, where it turns a turbine or generates electricity some other way.

Pumped hydro: This is a method of storing city-sized amounts of energy, and it works like this: When electricity is cheap (for example, when a stiff wind is turning your turbines really fast), you pump water up a hill into a reservoir; then, when demand for power goes up, you let the water flow back down the hill, using it to spin a turbine and generate more electricity.

Thermal storage: The notion here is that when electricity is cheap, you use it to heat up some material. Then, when you need more electricity, you use the heat to generate power via a heat engine. This can work at 50 or 60 percent efficiency, which isn’t bad. Engineers know about many materials that can stay hot for a long time without losing much energy; the most promising approach, which some scientists and companies are working on, is to store the heat in molten salt.

Fuel cell: Fuel cells get their energy from a chemical reaction between two gases—usually hydrogen and oxygen—and their only by-product is water. We could use electricity from a solar or wind farm to create hydrogen, store the hydrogen as compressed gas or in another form, and then put it in a fuel cell to generate electricity on demand. In effect, we’d be using clean electricity to create a carbon-free fuel that could be stored for years and turned back into electricity at a moment’s notice. And we would solve the location problem I mentioned earlier; although you can’t ship sunlight in a railcar, you can turn it into fuel first and then ship it any way you like.

Hydrogen is also a very lightweight gas, which makes it hard to store within a reasonably sized container. It’s easier to store the gas if you pressurize it (you can squeeze more into the same-volume container), but because hydrogen molecules are so small, when they’re under pressure, they can actually migrate through metals. It’s as if your gas tank slowly leaked gas as you filled up.



We could keep making electricity as we do now, with natural gas and coal, but suck up the carbon dioxide before it hits the atmosphere. That’s called carbon capture and storage, and it involves installing special devices at fossil-fuel plants to absorb emissions. These “point capture” devices have existed for decades. DAC is a much bigger technical challenge than point capture, thanks to the low concentration of carbon dioxide in the air. When emissions come directly out of a coal plant, they’re highly concentrated, in the range of 10 percent carbon dioxide, but once they’re in the atmosphere, where DAC operates, they disperse widely. Pick one molecule at random out of the atmosphere and the odds that it will be carbon dioxide are just 1 in 2,500.



To sum up, the path to zero emissions in manufacturing looks like this: Electrify every process possible. This is going to take a lot of innovation. Get that electricity from a power grid that’s been decarbonized. This also will take a lot of innovation. Use carbon capture to absorb the remaining emissions. And so will this. Use materials more efficiently. Same.



Impact of steel/concrete on climate change:

Americans use as much steel as cement—so that’s another 600 pounds per person, every year, not counting the steel we recycle and use again.

Making 1 ton of steel produces about 1.8 tons of carbon dioxide. By 2050 the world will be producing roughly 2.8 billion tons every year. That adds up to 5 billion tons of carbon dioxide released every year by mid-century, just from making steel, unless we find a new, climate-friendly way to do it.

To make concrete, you mix together gravel, sand, water, and cement. The first three of these are relatively easy; it’s the cement that is a problem for the climate. To make cement, you need calcium. To get calcium, you start with limestone—which contains calcium plus carbon and oxygen—and burn it in a furnace along with some other materials. Given the presence of carbon and oxygen, you can probably see where this is going. After burning the limestone, you end up with the thing you want—calcium for your cement—plus something you don’t want: carbon dioxide. Nobody knows of a way to make cement without going through this process. Make a ton of cement, and you’ll get a ton of carbon dioxide. Between now and 2050, the world’s annual cement production will go up a bit—as the building boom slows in China and picks up in smaller developing countries—before settling back down near 4 billion tons a year, roughly where it is today.



Impact of plastic on climate change:

When we make cement or steel, we release carbon dioxide as an inevitable by-product, but when we make a plastic, around half of the carbon stays in the plastic. Plastics can take hundreds of years to degrade. Purely in terms of emissions, the carbon in plastics is not such bad news. Because plastics take so long to degrade, all the carbon atoms that go into them are atoms that won’t go into the atmosphere and drive up the temperature—at least not for a very long time.

Clean electricity would help us solve another problem too: making plastics. If enough pieces come together, plastics could one day become a carbon sink—a way to remove carbon rather than emit it. Here’s how we could do it. First, we would need a zero-carbon way to power the refining process. We could do that with clean electricity or with hydrogen produced from clean electricity. Then we’d need a way to get the carbon for our plastics without burning coal. One idea is to remove carbon dioxide from the air and extract the carbon, though that’s an expensive process. Another approach that various companies are working on is to get carbon from plants. Finally, we’d need a zero-carbon source of heat—which would likely also be clean electricity, hydrogen, or natural gas fitted with a device to capture the carbon it emits. If all these pieces come together, we could make plastics with net-negative emissions. In effect, we’d find a way to take carbon out of the air (using plants or some other method) and put it into a bottle or other plastic product, where it would stay for decades or centuries, with no additional emissions. We’d be socking away more carbon than we were putting out.



You need to understand where emissions come from when we make things. I think of it in three stages: We emit greenhouse gases (1) when we use fossil fuels to generate the electricity that factories need to run their operations; (2) when we use them to generate heat needed for different manufacturing processes, like melting iron ore to make steel; and (3) when we actually make these materials, like the way cement manufacturing inevitably creates carbon dioxide.

How can we generate heat without burning fossil fuels? If you don’t need super-high temperatures, you can use electric heat pumps and other technologies. But when you’re looking for temperatures in the thousands of degrees, electricity isn’t an economical option—at least not with today’s technology. You’ll have to either use nuclear power or burn fossil fuels and grab the emissions with carbon-capture devices. Unfortunately, carbon capture doesn’t come for free. It adds to the manufacturer’s cost and gets passed on to the consumer.

One approach is to take recycled carbon dioxide—possibly captured during the process of making cement—and inject it back into the cement before it’s used at the construction site. The company that’s pursuing this idea has several dozen customers already, including Microsoft and McDonald’s; so far it’s only able to reduce emissions by around 10 percent, though it hopes to get to 33 percent eventually.



As people get richer, they eat more calories, and in particular they eat more meat and dairy. And producing meat and dairy will require us to grow even more food. A chicken, for example, has to eat two calories’ worth of grain to give us one calorie of poultry—that is, you have to feed a chicken twice as many calories as you’ll get from the chicken when you eat it. A pig eats three times as many calories as we get when we eat it. For cows, the ratio is highest of all: six calories of feed for every calorie of beef. In other words, the more calories we get from these meat sources, the more plants we need to grow for the meat.

Around the world, there are roughly a billion cattle raised for beef and dairy. The methane they burp and fart out every year has the same warming effect as 2 billion tons of carbon dioxide, accounting for about 4 percent of all global emissions.

When poop decomposes, it releases a mix of powerful greenhouse gases—mostly nitrous oxide, plus some methane, sulfur, and ammonia. About half of poop-related emissions come from pig manure, and the rest from cow manure. There’s so much animal poop that it’s actually the second-biggest cause of emissions in agriculture, behind enteric fermentation.



Technology can help in reducing food related emission. For example, two companies are working on invisible, plant-based coatings that extend the life of fruits and vegetables; they’re edible, and they don’t affect the taste at all. Another has developed a “smart bin” that uses image recognition to track how much food is wasted in a house or business. It gives you a report on how much you threw away, along with its cost and its carbon footprint. The system may sound invasive, but giving people more information can help them make better choices.



To grow crops, you want tons of nitrogen—way more than you would ever find in a natural setting. Adding nitrogen is how you get corn to grow 10 feet high and produce enormous quantities of seed. Oddly, most plants can’t make their own nitrogen; instead, they get it from ammonia in the soil, where it’s created by various microorganisms. A plant will keep growing as long as it can get nitrogen, and it’ll stop once the nitrogen is all used up. That’s why adding it boosts growth.

There are other downsides to synthetic fertilizer. To make it, we have to produce ammonia, a process that requires heat, which we get by burning natural gas, which produces greenhouse gases. Then, to move it from the facility where it’s made to the warehouse where it’s stored (like the place I visited in Tanzania) and eventually the farm where it’s used, we load it on trucks that are powered by gasoline. Finally, after the fertilizer is applied to soil, much of the nitrogen that it contains never gets absorbed by the plant. In fact, worldwide, crops take up less than half the nitrogen applied to farm fields. The rest runs off into ground or surface waters, causing pollution, or escapes into the air in the form of nitrous oxide—which, you may recall, has 265 times the global-warming potential of carbon dioxide. All told, fertilizers were responsible for roughly 1.3 billion tons of greenhouse gas emissions in 2010.



There’s the immediate and obvious impact of deforestation—if the trees are burned down, for example, they quickly release all the carbon dioxide they contain—but it also causes damage that’s harder to see. When you take a tree out of the ground, you disturb the soil, and it turns out that there’s a lot of carbon stored up in soil (in fact, there’s more carbon in soil than in the atmosphere and all plant life combined). When you start removing trees, that stored carbon gets released into the atmosphere as carbon dioxide.

You might’ve heard about one forest-related solution for climate change: planting trees as a way to capture carbon dioxide from the atmosphere. Although it sounds like a simple idea—the cheapest, lowest-tech carbon capture imaginable—and it has obvious appeal for all of us who love trees, it actually opens up a very complicated subject. It needs to be studied a lot more, but for now its effect on climate change appears to be overblown.

How much carbon dioxide can a tree absorb in its lifetime? It varies, but a good rule of thumb is 4 tons over the course of 40 years.

In what part of the world will you plant the tree? On balance, trees in snowy areas cause more warming than cooling, because they’re darker than the snow and ice beneath them and dark things absorb more heat than light things do. On the other hand, trees in tropical forests cause more cooling than warming, because they release a lot of moisture, which becomes clouds, which reflect sunlight. Trees in the midlatitudes—between the tropics and the polar circles—are more or less a wash.

Was anything else growing in that spot? If, for example, you eliminate a soybean farm and replace it with a forest, you’ve reduced the total amount of soybeans available, which will drive up their price, making it more likely that someone will cut down trees somewhere else to grow soybeans. This will offset at least some of the good you do by planting your trees.

Taking all these factors into account, the math suggests you’d need somewhere around 50 acres’ worth of trees, planted in tropical areas, to absorb the emissions produced by an average American in her lifetime. Multiply that by the population of the United States, and you get more than 16 billion acres, or 25 million square miles, roughly half the landmass of the world. Those trees would have to be maintained forever. And that’s just for the United States—we haven’t accounted for any other country’s emissions.



On alternative fuels:

Another way to get to zero is to switch to alternative liquid fuels that use carbon that was already in the atmosphere. When you burn these fuels, you’re not adding extra carbon to the air—you’re just returning the same carbon to where it was when the fuel was made.

Corn-based ethanol isn’t zero carbon, and depending on how it’s made, it may not even be low carbon. Growing the crops requires fertilizer. The refining process, when the plants get turned into fuel, produces emissions too. And growing crops for fuel takes up land that might otherwise be used for growing food—possibly forcing farmers to cut down forests so they have someplace to grow food crops.



Here’s what that means in practical terms. According to a 2017 study by two mechanical engineers at Carnegie Mellon University, an electric cargo truck capable of going 600 miles on a single charge would need so many batteries that it would have to carry 25 percent less cargo. And a truck with a 900-mile range is out of the question: It would need so many batteries that it could hardly carry any cargo at all.

Not long ago, my friend Warren Buffett and I were talking about how the world might decarbonize airplanes. Warren asked, “Why can’t we run a jumbo jet on batteries?” He already knew that when a jet takes off, the fuel it’s carrying accounts for 20 to 40 percent of its weight. So when I told him this startling fact—that you’d need 35 times more batteries by weight to get the same energy as jet fuel—he understood immediately. The more power you need, the heavier your plane gets. At some point, it’s so heavy that it can’t get off the ground. Warren smiled, nodded, and just said, “Ah.”



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.

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.



We can reduce Green Premiums by making carbon-free things cheaper (which involves technical innovation), by making carbon-emitting things more expensive (which involves policy innovation), or by doing some of both



We already know how to take the salt out of seawater and make it drinkable, but the process takes a lot of energy, as does moving the water from the ocean to the desalination facility and then from the facility to whoever needs it. (This means that, like so many things, the water problem is ultimately an energy problem: With enough cheap, clean energy, we can make all the potable water we’ll ever need.)