18.5: Summary

I’ve discussed a number of possible ways to achieve the negative emissions we will need to stay well below a 2°C total temperature rise. There is no single technology that can do it all—or even a small handful of approaches. We will need many different techniques, and all will need to achieve heroic scales—on the order of billions of tons of CO₂ per year—in relatively short times.

Figure 18.5.1 Summary of negative emissions technologies. From Sabine Fuss, Mercator Institute.

Figure 18.5.1 summarizes most of the technologies we have discussed in this chapter. Achieving 20 billion tons per year of negative emissions would require almost all of these operating at full capacity, and probably more beyond that.

Ultimately the removal of CO₂ from the air is very similar to trash collection in cities today. It is an activity that we must do to maintain a livable environment. We simply will have to pay for it. Some technologies to reduce CO₂ emissions, such as renewable energy, generate a useful product (electricity), and once renewable energy reached the price of fossil fuels it became easier to replace the fossil sources. But achieving negative emissions does not replace an existing technology, and so it is harder than developing renewable energy. There is no price incentive for negative emissions, because the price we have been paying to dump CO₂ into the atmosphere is zero!

Figure 18.5.2 Potential costs and capacities of a number of prominent negative emissions technologies. From Sabine Fuss, Mercator Institute.

Figure 18.5.2 from the Mercator Institute in Germany gives one current estimate of the range of costs, and potential volumes, for the major negative emissions options discussed here. At this point it is not possible to produce precise estimates; the impacts of land use, energy, and cost have not been established, and the technologies are still being developed. The natural options such as afforestation and soil carbon sequestration are most likely to be the least expensive but do not add up to the 20 billion tons we will need at the end of the century. Nor does this estimate give options like bioenergy with carbon capture and storage, or direct air capture, an unlimited estimated capacity; they will ultimately have limits due to land use and cost of capital to build them. It appears most likely that we will need many, if not most, of these approaches (and some not yet invented!) to achieve our climate goals.

We could estimate the average from Figure 18.5.2 as around $100/ ton of CO₂ removed (averaging the cost of the less expensive technologies and hoping that we need a minimum of direct air capture). At that cost, which seems achievable by the end of the century, the 10 billion tons required in 2050 would cost the world $1 trillion per year—a huge number, but only about 1% of today’s world gross domestic product (GDP) of $100 trillion. (By 2050, world GDP is expected to be about $220 trillion.) The United States, with a GDP today of about $18 trillion, spends on the order of $200 billion to manage its garbage—a remarkably similar 1%. Can we spend 1% of our world economy cleaning up the mess we have made of our atmosphere over the last 200 years? Let’s hope we can.

And the path that we follow is not just a function of negative emissions options. As you have learned throughout this book, there are dozens or even hundreds of choices that society has to make about the rate of carbon-free energy adoption, energy efficiency, land use, population, and many other factors. Each of these choices contributes to the pathway that we take through future climate space. That path is not yet decided, and society is grappling with the mechanisms to weigh and implement the various options. By reading this book, you have made yourself an educated contributor to that discussion. Whether they be technological, organizational, political, inspirational, or real muscles, you are now ready to apply your muscles to bending the curve.

Negative emissions technology and evaluation are just in their infancy today, rather like renewable energy was in the 1970s. Some of the directions we need to take are clear, but the details of technology combinations, system approaches, and overall trade-offs are not yet apparent. What is obvious is that cleaning up the atmosphere to levels we consider livable will be a massive effort—one that the students of today (you readers of this book) will spend their careers making successful. It is no small effort and will likely be the most important science and technology effort of this century. Go forth and succeed!