 Illustration by Jaina Modi By Bradley Kelton 19th-century England stank–literally. In the era before sewage treatment became widespread, the burgeoning metropolis of London faced an unpleasant problem. As the city’s population tripled, the limited number of cesspools led to effluent leaking out of the system and accumulating on the banks of the River Thames. The smell had become so unbearable that Charles Dickens remarked in 1858 that even a short whiff was “of a most head-and-stomach distending nature.” The situation came to a head in August 1858 when the scorching summer heat propelled the smell into the air and the accompanying cholera outbreaks drove mass public outcry and disgust. Enter Sir Joseph Bazalgette, an early civil engineer who proposed using a network of drainage pipes to divert wastewater away from the city. The system he built drastically improved public health and ended the “Great Stink” for a reasonably low annual expense (Warburton, 2025). While others allowed London’s sewage problem to fester, Bazalgette recognized the importance of acting upon the crisis before it exacted a human cost. Today, humanity is facing a similar crisis, at least according to Columbia professor of Earth and Environmental Sciences Peter Kelemen. Kelemen claims that the accumulation of greenhouse gases, namely carbon dioxide (CO2), which warm the planet is analogous to the accumulation of sewage waste on the banks of the River Thames two centuries ago (Rathi, 2021). If this is true, then a long-term solution to global warming might demand some way to retroactively reduce the concentration of these gases in the atmosphere. It turns out that rock uptake on Earth’s surface does this naturally but at a very slow rate. In an effort to better understand this process, called carbon sequestration, Kelemen and his colleague Jürg Matter set out to the nation of Oman in 2008. There, they studied mafic rocks–rich in magnesium and calcium–and found something rather remarkable.
But even before Kelemen had set out, it was widely known that these mafic rocks had carbon storage potential because of the two minerals that make them up: olivine and pyroxene. Like most minerals on Earth’s surface, these minerals are silicates, characterized by the silicon tetrahedron. Olivine contains individual tetrahedra, while in pyroxene they form short chains. Each mineral also contains cations that are weakly bonded to the silicate structure. These cations range in type, but by far the two most common are calcium and magnesium. To react with atmospheric CO2, all that’s needed is the weak acid that forms naturally, especially when atmospheric CO2 levels are high–as they are today. In fact, it forms the same way that bubbles emerge when a child blows through a straw into a cup of water. The compound that results, called carbonic acid (H2CO3), is an extremely weak acid that dissolves in the presence of these mafic minerals, creating a salt such as calcite (CaCO3) or magnesite (MgCO3) along with some water and what is essentially sand (SiO2). In this carbonate form, CO2 gas is unlikely to re-enter the atmosphere for millions of years (Nilsen, 2023). Because of the complexity and extremely slow rate of this reaction, it was thought that the role of rocks in sequestering carbon was basically negligible, at least as far as humans are concerned. Part of the reason for this is that olivine and pyroxene are generally not found at Earth’s surface, as they usually form under conditions of intense heat and pressure, such as in the upper mantle. Kelemen found, however, that due to tectonic activity, there is actually far more exposed olivine and pyroxene at the surface than previously thought, suggesting an enhanced potential rate of up to 1 gigaton of carbon dioxide captured per year (Kelemen & Matter, 2008). This was a breakthrough in the field, as it provided a scalable blueprint to manage the carbon waste problem. Today, there are more than 50 commercial facilities across the world that have adopted this blueprint and dramatically scaled up carbon capture. These facilities, called Direct Air Capture (DAC) plants, draw in air using a massive system of fans and run it through an alkaline solution to produce carbonate compounds from atmospheric CO2. The resulting carbonate pellets are then stored in a large tank where they are heated to re-release CO2 gas which is most often transported underground and reacted again with the mafic minerals, olivine or pyroxene, for long-term sequestration (Budinis et al., 2024). The remaining “clean” air mixture is then released back into the atmosphere. Optimistic estimates state that this process could potentially negate 85-90% of annual emissions, but other recent studies suggest this figure may be as low as 11% (Kubota, 2019). Needless to say, there is still a great deal of uncertainty and debate within the scientific community regarding the efficacy of these technologies and the practicality of implementing them. For one, the numbers don’t favor carbon capture as the main solution to global warming. To put it into perspective, even if every single one of the planned 700 carbon capture facilities is operational by 2050, we will still be over 1,000 facilities short of sequestering enough CO2 to avoid a minimum 3 ℃ warming projected by the International Panel on Climate Change (IPCC) in 2023. What’s perhaps even more troubling is that many of these facilities aren’t running on renewable energy, so their net decarbonization effect is extremely limited (Kubota, 2019). Debates over carbon capture have made it clear that global warming is no “Great Stink,” and the solution won’t be as simple as building a system that manages our carbon waste while we continue to emit at current levels. The reality is that any solution to global warming must address emissions levels. The 19th-century Londoners couldn’t choose to stop producing sewage waste, but the same is not true for greenhouse gas emissions today. It is undeniable that solving this problem will require massive international cooperation and investment in renewable energy. Carbon capture is a remarkable technology that can be a part of that solution; ultimately, though, it’s clear our climate needs less, not more, human interference. References Dickens, C. In M. D. Cerjat (Ed.), Letters of Charles Dickens: 1833–1870 [Letter to M. D. Cerjat]. Google Books. https://books.google.com/books?id=INkAes9Y5AYC&pg=PP1#v=onepage&q=Head-and&f=false Warburton, S. (2025, March 28). Dickens and The Great Stink of 1858. Royal Museums Greenwich. https://www.rmg.co.uk/stories/maritime-history/library-archive/dickens-great-stink-1858 Rathi, A. (2021, September 21). We Pay to Treat Waste Water, Why Not Waste Carbon? Green Fiscal Policy Network. https://greenfiscalpolicy.org/we-pay-to-treat-waste-water-why-not-waste-carbon/ Kelemen, P.B. & Matter, J. (2008, November 11). In situ carbonation of peridotite for CO2 storage, Proc. Natl. Acad. Sci. U.S.A. 105 (45) 17295-17300. https://doi.org/10.1073/pnas.0805794105 Nilsen, C. (2023, May 23). Olivine Weathering. Works in Progress. https://worksinprogress.co/issue/olivine-weathering/ Budinis, S., Fajardy, M., & Greenfield, C. (2024, April 25). Carbon Capture Utilisation and Storage. International Energy Agency. https://www.iea.org/energy-system/carbon-capture-utilisation-and-storage Kubota, T. (2019, October 25). Stanford study casts doubt on carbon capture. Stanford Report, Stanford University. https://news.stanford.edu/stories/2019/10/study-casts-doubt-carbon-capture The Intergovernmental Panel on Climate Change. (2023, March 19). AR6 Synthesis Report: Climate Change 2023. https://www.ipcc.ch/sr15/
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