Human activity has emitted so much carbon dioxide (CO2) into the atmosphere that current reduction efforts alone—while still critical—aren’t happening fast enough to prevent significant and irreversible effects of climate change. Currently, the funds and technology required to get global emissions rates to net zero rapidly are insufficient or don’t exist. But by combining emissions reductions with carbon dioxide removal we can balance the carbon budget.
There are many methods of removing CO2 from the air and oceans, including creating new forests, burying wood, and making new carbon-based minerals. One approach, direct air capture, has grown in prominence, reflecting advances in climate science, technology, commercial practice, policy, and investments into companies and projects.
What is direct air capture?
Direct air capture works by sucking in air then filtering it to remove CO2 that has built up over time and still sits in the atmosphere. To be effective, direct air capture must draw a lot of air into separating equipment like filter banks or cooling towers (this is similar to the small-scale systems that have scrubbed CO2 from air in spacecraft and submarines for decades). From there, CO2 filtering typically involves a chemical process that binds the CO2 for release later. The most commonly used chemical compounds are liquid solvents or solid sorbents, but other chemical, electrical, and physical processes could also work.
After the filtering process, the captured CO2 is usually stored in one of two ways. The most important is geological storage, which keeps CO2 out of the air and oceans indefinitely in deep geological formations (more than half a mile down) and offers the clearest climate benefits. The second is by storing the CO2 into products like concrete, which offers clearer commercial benefits. In addition, CO2 can be recycled into fuels and chemicals, which prevents net-new carbon dioxide from being released but does not count as a carbon removal solution.
The advantages of direct air capture
Direct air capture has many advantages as a CO2 removal approach:
First and foremost, it’s scalable. In effect, there are no practical limits to our ability to scrub CO2 from the sky or store it in deep geological formations around the world. This means scaling can be fast and removals profound.
It’s straightforward. The devices remove CO2 from the air, a meter measures it, and operators store and monitor that CO2. It's clearly additional (meaning it only happens with financial and human intervention), easily verified, and durable (stored for many hundreds of years or more).
Direct air capture has a small physical footprint. Typical direct air capture systems do the carbon removal work of trees with 1,000 to 2,000 times less space. This leaves more room for conservation, agriculture, rewilding, and other important work.
It can be done anywhere with low-carbon energy and CO2 storage options. Globally, our atmosphere mixes fully every two weeks, meaning that CO2 released in China or Australia arrives over the US and vice-versa in this amount of time. Because of this, direct air capture facilities can be anywhere and still have a climate benefit—as long as there is sufficient available clean energy and options for CO2 storage or use nearby. This reduces competition for land and provides opportunities for economic development in regions with the right resources.
Finally, and most critically, direct air capture is a backstop technology. While reducing emissions remains the top priority, there are certain types of emissions that are either very hard or very expensive to abate. The last fraction of hard-to-abate emissions can be managed through direct air capture, effectively capping global costs to reach net-zero emissions. In fact, the more rapidly direct air capture scales and deploys, the less total energy and total cost needed to achieve key climate goals.
Challenges and concerns of direct air capture
Like all climate mitigation approaches, direct air capture has challenges. The primary challenge today is cost. Today’s systems have prices between $600 and $1100/ton CO2 removed. Although the costs will come down over time through deployment and wider adoption, today’s high costs are a barrier to investment and deployment.
Another challenge is around the energy requirements associated with direct air capture. Pulling one million tons per year of CO2 out of the air requires roughly 200-300 megawatts of zero-carbon energy (a combination of heat and electricity). Given the limited supply of zero-carbon energy available today, there is a valid question about whether this is the best use of that resource today.
Finally, there is the question of environmental risks and community burdens of direct air capture. Experience to date suggests that the total environmental burdens and consequences of direct air capture are among the lowest of any clean energy and climate technology. But since direct air capture systems involve heavy equipment and chemicals, questions remain over the full environmental risks and burdens to communities, especially given the limited commercial deployment. Although most direct air capture systems will be in remote locations, not near communities, and pose no serious environmental risks, reasonable concerns must be addressed before permitting and building future direct air capture projects.
Why the excitement now?
Although current climate science and added urgency from organizations like IPCC have driven interest in direct air capture, other important advances have fed broad interest and excitement about its potential. Since 2017, direct air capture technology has matured greatly, including the deployment and operation of many projects around the world. Costs have dropped, new pathways have opened, and investment has helped create over 50 companies in the last five years. Total investment to date has exceeded $1.5 billion. The world will soon have two new, large facilities, with one opening in Iceland in 2023 and another project under construction in Texas. Both facilities have substantial commercial offtake agreements from aviation, energy, insurance, and tech companies.
In part, interest results from new policy advancements. In the US, these include large incentives for direct air capture in the Inflation Reduction Act, including $3.5 billion for regional direct air capture hubs research and other research, development and demonstration. In addition, California has amended its Low-Carbon Fuel Standard to allow direct air capture as a compliance mechanism, and proposed legislation in the US would create government procurement programs along with a prize for direct air capture. The US Department of Energy is beginning a pilot program to purchase valid, durable carbon dioxide removal, including direct air capture.
Other programs around the world reflect this growing interest. In the UK and EU, governments have promised CO2 removal purchases this decade, which will likely include direct air capture. Research programs have begun in Canada, the UK, Germany, Japan, and China. Developing nations increasingly see direct air capture as a potential new industry and hope to take advantage of their natural resources to expand energy access while being paid to remove CO2 from the air and oceans.
Personal note on the future of direct air capture
I’m pleased to have played a small role in direct air capture’s new prominence. I’ve had the good fortune of being at direct air capture project groundbreakings and ribbon cuttings, led the first ever government grants program for direct air capture, worked with scientists to develop new direct air capture technologies, published analysis a decade ago on the need for direct air capture, and testified before the US congress on the benefits and needs of direct air capture on three separate occasions. Through my experience in direct air capture over 13 years, I believe that smart investment, policy, deployment, and community engagement will convert the promise of direct air capture into thousands of projects that will help avoid the worst outcomes of climate change and restore some of the natural balance to the world.