Human actions are releasing billions of tons of carbon dioxide into our atmosphere annually, contributing to rising global temperatures and increased incidents of extreme weather. As nations confront the challenges posed by climate change and explore effective strategies to drastically reduce carbon emissions, one promising avenue is the advancement of carbon dioxide removal (CDR) technologies. These innovations aim to extract carbon dioxide directly from the air and securely store it for extended periods.
Contrarily, carbon capture and storage (CCS) technologies focus on eliminating carbon dioxide at its production sites, such as fossil-fuel plants. In contrast, CDR seeks to eliminate carbon dioxide that is already present in the atmosphere.
A recentreport from the American Physical Society, led by a physicist from MIT, provides a comprehensive overview of the leading experimental CDR methods and assesses their fundamental physical limitations. The report emphasizes techniques with the highest potential for removing gigatons of carbon dioxide yearly, a scale necessary for climate stabilization.
Commissioned by the American Physical Society’s Panel on Public Affairs, this report was published last week in the journal PRX. Chaired by MIT physics professor Washington Taylor, this report sheds light on the physical limitations of CDR and underscores the importance of pursuing these methods in conjunction with global carbon emission reduction efforts.
Q: What prompted you to evaluate carbon dioxide removal systems from a physical science viewpoint?
A: The primary driver of climate change is our extraction of carbon stored in Earth for millions of years, releasing it into the atmosphere and causing global warming. Recently, there’s been escalating interest from both governmental and private sectors in developing technologies to directly remove CO2 from the air.
Understanding how to manage atmospheric carbon is crucial in mitigating our environmental impact. Thus, it’s vital to explore whether we can influence carbon levels not only by altering emission profiles but also by directly extracting carbon from the atmosphere. Physics plays a pivotal role here, as possibilities are significantly limited by thermodynamics and material constraints.
Q: Which carbon dioxide removal techniques did you examine?
A: Most methods are still in their infancy, resembling a ‘Wild West’ scenario with various companies proposing ways to mitigate atmospheric carbon. In our report, we categorize CDR processes into two distinct classes: cyclic and once-through.
To illustrate, picture being in a boat with a hole that’s causing it to take on water rapidly. We urgently want to seal that hole, but even after doing so, we must eliminate the excess water to prevent sinking or capsizing. Consider two methods to remove water:
The first is akin to using a sponge; this cyclic approach allows us to absorb water, wring it out, and reuse the sponge. An example is chemical “direct air capture” (DAC), where large systems draw air over materials that trap CO2. Once saturated, the system stores the carbon in a secure repository, enabling the material to be reused in a cyclic manner.
The second approach parallels using disposable paper towels. After soaking up water, we would throw them overboard after a single use. Once-through CDR methods, like enhanced rock weathering, speed up a natural reaction in which certain rocks absorb atmospheric carbon when exposed to air. This natural weathering process removes approximately 1 gigaton of carbon annually globally. Enhanced rock weathering involves mining specific rocks, grinding them down to a fine powder, and spreading them out to absorb CO2 all at once.
The key distinction between cyclic and once-through processes is that cyclic methods face limits imposed by the second law of thermodynamics, which dictates energy requirements. For example, our analysis shows that capturing a gigaton of CO2 through DAC would necessitate energy equivalent to the annual electric consumption of Virginia, while current systems require three to ten times that energy for far smaller carbon capture.
Conversely, once-through processes, while circumventing some energy limitations, encounter material constraints governed by chemical principles. For methods like enhanced rock weathering, capturing a gigaton of CO2 would require around a billion tons of rock.
Ultimately, installing engineered systems for gigaton-scale carbon removal necessitates significant physical materials, air movement, and energy. Yet, large-scale emissions reductions will also face similar challenges.
Q: What conclusions does the report draw about the feasibility of atmospheric carbon removal?
A: Initially, we believed CDR would demand excessive energy, a consequence of the second law of thermodynamics, irrespective of the method used. However, we found a nuanced understanding between cyclic and once-through systems. While one perspective suggests CDR can function as a panacea, allowing us to neglect emission reductions, the reality is that large-scale CDR will be both costly and energy-intensive. Conversely, some argue that even discussing CDR undermines emissions reduction efforts. Our report advocates a balanced stance: CDR is not an all-encompassing solution, nor should it be dismissed. If we genuinely aim to combat climate change, we will likely need substantial CDR alongside rigorous emissions reductions.
The report emphasizes the necessity of developing a policy framework that incentivizes both emissions reductions and CDR, facilitating market optimization of climate solutions. Since reducing emissions is often more straightforward and economical than atmospheric carbon removal, comprehending CDR’s complexities should motivate urgent emissions cuts.
Personally, I find it encouraging that we understand what it will take to lower emissions and utilize CDR to diminish CO2 levels. The challenge now rests in the societal and economic realms. Humanity possesses the potential to tackle these challenges, and I hope we can reach a consensus that leads to actions beneficial to both people and the planet’s ecosystems before we face even greater challenges.
Environment, Science, Technology
Photo credit & article inspired by: Massachusetts Institute of Technology
