View course on architecturalrecord.com »

THE CLIMATE clock is ticking. Scien­tists say that to avert the worst effects of the climate crisis, we need to keep the increase in average global temperatures under 1.5 degrees Cel­sius, as compared to preindustrial levels. And we need to act fast, slashing human-caused greenhouse emissions by almost half by 2030 and reaching net zero emissions by midcentury.

Image © Martha Schwartz Partners

FOR THE DESERT surrounding an airport in the Middle East, Martha Schwartz Partners proposes a greened landscape combined with high-tech carbon-removal strategies.

However, many of those same experts say that we are on a trajectory to overshoot these marks, especially if we rely solely on avoiding emissions. The United Nations authority on global-warming science, the Intergovernmental Panel on Climate Change, says that all its models for meeting the 1.5 threshold rely, to some extent, on technologies that actually take carbon out of the atmosphere—an approach called CDR, or carbon dioxide removal.

Still, advocates of CDR emphasize that it can’t be considered a substitute for drastically cutting emissions. Phasing out fossil fuels, expanding renewable energy, and accelerating efficiency measures, they maintain, remain absolutely essential, but these mitigation methods alone will be insufficient to prevent climate catastrophe. “It isn’t ‘either/or’ but ‘both/and,’ ” says Giana Amador, policy director and cofounder of Carbon180, a nonprofit that promotes carbon-removal strategy. “The climate math is telling us that we will have to remove 10 gigatons of carbon annually by 2050, in addition to reaching net zero,” she says.

What qualifies as CDR? Also referred to as carbon drawdown, or negative-emissions technologies, the term refers to a host of strategies, including those that are nature-based and well understood, such as reforestation, wetland restoration, and improved agricultural practices, as well as still-emerging methods like direct air capture (DAC)—a higher-tech, and still very expensive, solution that relies on fans and chemical processes to suck CO₂ directly from the air.

All of these removal methods have different levels of permanence, or what is known in carbon-speak, as “durability”—the amount of time that the carbon is sequestered. The natural solutions tend to be relatively short-lived (plants eventually die and decay, releasing greenhouse gases), while some of the engineered ones, such as DAC, can be used to store carbon essentially forever, but it depends on how the collected CO₂ is disposed of.

Carbon collected in this way can be used in the manufacture of a variety of products, including fuels and building materials. And, according to Carbon180, there is the potential for a nearly $6 billion global market for this so-called “waste carbon.” But the most durable end use for carbon captured via DAC, and the best one from a climate perspective, says Amador, is geologic storage—putting it underground in rock formations. Though some observers might worry about the potential for induced seismicity, groundwater contamination, and leakage with this method, Carbon180 says that these “are unlikely to occur and can be easily mitigated.”

Image © SOM

SOM’S URBAN SEQUOIA (above) incorporates CDR technologies such as algae-filled facades and DAC (below).

Image © SOM

Image © SOM

Over 60 years, the tower would absorb 350 percent of its embodied carbon, says the firm.