Imagine you have a budget of 1 billion dollars and 10 years, and you want to do the most to eliminate emissions of greenhouse gases. How would you spend your time and money? What solutions would you pursue? What factors would you consider to make your decision? In this article, we’ll propose a framework for you to use as you evaluate which of the many solutions would be most impactful.

First, you’ll need to find a way to sort through the many solutions available. One tool you might find useful is a set of categories we call the Grand Challenges.

The Grand Challenges help us group the sources of human emissions into five categories. When we’re examining possible solutions to emissions, it makes sense to use those same five categories. However, as with the sources of emissions, the story gets complicated quickly. The ways in which humanity emits greenhouse gases are complex and interrelated. As a result, any solution within any Grand Challenge will inevitably need to consider linkages to other Grand Challenges.

For example, designing our buildings to heat and cool themselves without emitting carbon would be nice, but what if those designs require lots of concrete? In other words, just as emission sources don’t always fit nicely within one category, neither do the solutions—and that’s a good thing! Take clean electricity. One solution for the “How We Plug In” Grand Challenge will make a positive impact on all the other Grand Challenges because it has us electrifying machines and systems that have historically run on fossil fuels, like vehicles and steelmaking.

So, to begin, let’s identify a few of the many different types of solutions within each Grand Challenge.

How We Plug In: Humans are using more and more electricity. Solutions that produce electricity through renewable energy such as wind and solar can make a big difference. One of the best things about renewables is that they’re scalable. That means you can design wind or solar production at just the right size for a single house, a building, or a city block. But there are also huge projects like dams, geothermal plants, and vast solar installations that can power whole cities. To utilize all that power when the Sun doesn’t shine, we’ll need more-advanced batteries and updated transmission lines to store and transport our electricity. One solution we will almost certainly need if we want to get to net zero is nuclear energy—both the fission we already have and the much more difficult to achieve (and still in development) fusion technology.

How We Make Things: We build our cities, roads, and rails using a whole lot of concrete and steel. Making these materials account for a huge portion of the carbon emissions the world produces. If we can get steel and cement to net zero, we can make an enormous difference in the rate of climate change. There are real alternatives to cement and steel, and one way to reduce our carbon production may be to use more of those alternatives, such as mass timber. We might also focus on process improvements—that is, putting together small changes to optimize factories, making them faster and more effective.

How We Grow Things: Some of the biggest solutions in this Grand Challenge come from livestock, which produce huge amounts of emissions through the methane they burp as well as from the ways we use land to raise them. One of the simplest solutions might be to just eat less meat, and that’s growing more feasible as more and more companies produce tastier and cheaper meat alternatives. But scientists are also developing vaccines and livestock feed that might cut down on the methane cows produce. Of course, it’s not all cows. We need to address deforestation and food waste. As much as 30% of all food gets wasted—that’s a problem we can solve! Finally, the fertilizers we use to grow the plants that we—and our livestock—eat also need improvement to reduce greenhouse gases like carbon and methane.

How We Get Around: Like renewables, electric vehicles are a solution we already have. They’re becoming more common and affordable each year. But to fully transition, the world needs more infrastructure such as fast public chargers and better batteries to compete with the range of gas-powered alternatives. Heavy vehicles that travel long distances—especially airplanes, cargo ships, and trucks—probably won’t ever be able to rely on electric power. For those forms of transportation, we need to develop alternatives like advanced biofuels, electrofuels, or even liquid hydrogen. Of course, there are lots of ways we can make our cities and infrastructure more efficient and encourage walking, biking, and public transit.

How We Keep Cool and Stay Warm: Though this is the smallest emitter among the Grand Challenges, we have several solutions available to us right now. And emissions from this Grand Challenge are set to increase dramatically unless we implement these solutions soon. By 2050, the number of air conditioners will more than double. Those AC units will use as much electricity as all of India and China do today. As climate change sparks ever-more-intense heat waves, air conditioning will save lives, but if we keep using outdated AC units powered by fossil fuel electricity, it will also make climate change a lot worse. Luckily, heat pumps, which are much more efficient than air conditioners, are widely available and are getting cheaper. We can also improve the ways we design and retrofit our buildings to make them smarter and more efficient. However, there are still lots of solutions in this Grand Challenge that require new innovations, including biofuels and new coolants to replace high-emitting refrigerants like freon.

Evaluating Solutions

There’s no single solution to climate change. We will need to put together lots of different solutions in every sector of the economy. The solutions we deploy to cut emissions will be chosen by policymakers, business leaders, and individuals like you. But not all solutions are equal when it comes to avoiding the worst impacts of climate change. How will deciders in different communities and countries know where to focus our energy, time, and resources?

First, local context is key. Communities have different economies, infrastructure, and resources available, as well as different sources of carbon emissions. That means that while some solutions will work in some places, in others, they’ll be less useful. While meat alternatives might be embraced in some urban regions, in ranching communities, that’s unrealistic. Solar energy might not be the best solution candidate near the Arctic Circle.

However, we can still evaluate and compare solutions overall based on three key criteria:

1. Time—How quickly can the solution start making an impact? If we somehow develop a technology to power the world with infinite, net-zero electricity, but it will take 100 years to implement, that would be too late to do much good.
2. Cost—What are the costs of developing and implementing the solution, and what is the green premium? Solutions will only be adopted by low- and middle-income countries if they are as cheap or cheaper than the fossil-fuel alternative. What are the solutions that can reach the lowest green premiums?
3. Impact potential—What percentage of the 51 billion tons of emissions will the solution eliminate? A solution that eliminates 1 million annual tons of greenhouse gas emissions sounds big, but that accounts for only 0.002% of annual emissions. Still, if the solution is cheap and quick enough—you might decide it’s worthwhile!

Let’s start with an example: There’s one kind of energy that is always usable, no matter what time of day or whether there’s wind or water around. It’s also a type of energy that produces very little carbon. This solution is called nuclear energy. Let’s look at our criteria to evaluate this solution.

1. Time: On the one hand, we already have access to nuclear energy. Nuclear fission generates over 70% of France’s electricity today. However, nuclear power plants take a long time to build—five to seven years, on top of the public processes involved. We also need research into things we don’t have yet, like nuclear fusion—a potentially clean form of power that produces no waste and can’t be used for weapons. Fusion is how the Sun makes energy, but it’s very difficult for humans to produce, and we are still perhaps decades away from the technology we need.
2. Cost: There are a few different types of cost associated with nuclear power. The first, of course, is money. Nuclear reactors take a long time and a lot of money to build. Building enough reactors to power a country would require massive government investment. Then, there’s also the environmental cost. But despite its bad reputation, nuclear energy is statistically one of the safest ways that humans generate electricity. However, nuclear power does create hazardous waste. We need innovations to figure out how to produce less waste and recycle and safely store what is produced.
3. Impact potential: This one is easy. Nuclear power—specifically fusion—could be a game changer, producing clean electricity to power all five Grand Challenges. It could provide us with almost unlimited, relatively cheap, and safe power. Per unit of energy produced, nuclear power uses less land and less building materials than just about any source of energy—including renewables.

Implementing Decarbonization Strategies

Now that you understand how we can categorize solutions and the criteria we can use to evaluate them, there are two more questions you need to consider: How do we get these solutions into widespread use? And who needs to help make them a reality? While these questions are still under debate, we can offer some likely answers.

First, we will need to stimulate innovation to develop solutions that aren’t yet ready for widespread use, and to make them cost competitive. This innovation may come from businesses as well as from government policies that support research and development and fund big, risky projects. In the case of nuclear, we need innovators and businesses to develop fusion technology, and we need policymakers to develop big answers to this big solution. This isn’t a solution that you can put on your roof like solar energy or buy with government rebates like heat pumps. This will require massive public works and funding programs at all levels of government.

Businesses and governments can use their purchasing power to promote solutions that are still in the early stages of development. This will help make them more competitive and, ultimately, more affordable for everyone. But individuals can make a difference, too. Consumer choices, like opting to buy green products even if they carry a slight premium, and behaviors like taking public transportation, can make a big difference.

So, now you have a framework for evaluating the many different solutions to the Grand Challenges, and you can weigh their relative value. And you know the fields of action we need to identify for each. Which solutions do you think are the most promising?