Enhanced weathering

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Enhanced weathering is a method of removing CO
from the atmosphere or oceans using processes which already occur in nature in which CO
dissolved in rain or sea water reacts with various minerals in rocks and soils eventually producing compounds which lock up the carbon.

Farming with crops and rocks to address global climate, food and soil security David J. Beerling, Jonathan R. Leake, Stephen P. Long, Julie D. Scholes, Jurriaan Ton, Paul N. Nelson, Michael Bird, Euripides Kantzas, Lyla L. Taylor, Binoy Sarkar, Mike Kelland, Evan DeLucia, Ilsa Kantola, Christoph Müller, Greg Rau, James Hansen; Nature Plants; 19 Feb 2018

The magnitude of future climate change could be moderated by immediately reducing the amount of CO
entering the atmosphere as a result of energy generation and by adopting strategies that actively remove CO
from it. Biogeochemical improvement of soils by adding crushed, fast-reacting silicate rocks to croplands is one such CO
-removal strategy. This approach has the potential to improve crop production, increase protection from pests and diseases, and restore soil fertility and structure. Managed croplands worldwide are already equipped for frequent rock dust additions to soils, making rapid adoption at scale feasible, and the potential benefits could generate financial incentives for widespread adoption in the agricultural sector. However, there are still obstacles to be surmounted. Audited field-scale assessments of the efficacy of CO
capture are urgently required together with detailed environmental monitoring. A cost-effective way to meet the rock requirements for CO
removal must be found, possibly involving the recycling of silicate waste materials. Finally, issues of public perception, trust and acceptance must also be addressed.

How Crushed Volcanic Rock in Farm Soil Could Help Slow Global Warming — and Boost Crops Georgina Gustin; Inside Climate News; 20 Feb 2018

Pulverizing volcanic rock and spreading the dust like fertilizer on farm soils could suck billions of tons of carbon from the atmosphere and boost crop yields on a warming planet with a growing population.

Why current negative-emissions strategies remain ‘magical thinking’ Nature; 21 Feb 2018

Decarbonization of the world’s economy would bring colossal disruption of the status quo. It’s a desire to avoid that change — political, financial and otherwise — that drives many of the climate sceptics. Still, as this journal has noted numerous times, it’s clear that many policymakers who argue that emissions must be curbed, and fast, don’t seem to appreciate the scale of what’s required.

According to the Intergovernmental Panel on Climate Change (IPCC), carbon emissions must peak in the next couple of decades and then fall steeply for the world to avoid a 2 °C rise. A peak in emissions seems possible given that the annual rise in carbon pollution stalled between 2014 and 2016, but it’s the projected decline that gives climate scientists nightmares.

The 2015 Paris agreement gave politicians an answer: negative emissions. Technology to reduce the amount of carbon already in the atmosphere will buy society valuable time. The agreement went as far as arguing that incorporating one such technology — bioenergy with carbon capture and storage (BECCS) — could even see the global temperature increase kept to 1.5 °C.

What would negative emissions look like? A Perspective this week in Nature Plants offers another glimpse, and it’s not pretty (D. J. Beerling et al. Nature Plants http://dx.doi.org/10.1038/s41477-018-0108-y; 2018). The review focuses on the idea of enhanced weathering, which aims to exploit how many rocks react with carbon dioxide and water to form alkaline solutions that, over time, find their way into the sea. It’s one of a number of proposed negative-emissions technologies.

In theory, enhanced weathering could lock up significant amounts of atmospheric carbon in the deep ocean. But the effort required is astounding. The article estimates that grinding up 10–50 tonnes of basalt rock and applying it to each of some 70 million hectares — an area about the size of Texas — of US agricultural land every year would soak up 13% of the annual global emissions from agriculture. That still leaves an awful lot of carbon up there, even after all the quarrying, grinding, transporting and spreading.

It’s not hard to see why many climate scientists have dismissed the near-impossible scale of required negative emissions as “magical thinking”. Or why the European Academies’ Science Advisory Council said in a report this month: “Negative emission technologies may have a useful role to play but, on the basis of current information, not at the levels required to compensate for inadequate mitigation measures.”

How green sand could capture billions of tons of carbon dioxide by James Temple; MIT Technology Review; 22 June 2020

Scientists are taking a harder look at using carbon-capturing rocks to counteract climate change, but lots of uncertainties remain.

Mineral weathering is one of the main mechanisms the planet uses to recycle carbon dioxide across geological time scales. The carbon dioxide captured in rainwater, in the form of carbonic acid, dissolves basic rocks and minerals—particularly those rich in silicate, calcium, and magnesium, like olivine. This produces bicarbonate, calcium ions, and other compounds that trickle their way into the oceans, where marine organisms digest them and convert them into the stable, solid calcium carbonate that makes up their shells and skeletons.

The chemical reactions free up hydrogen and oxygen in water to pull more carbon dioxide out of the air. Meanwhile, as corals and mollusks die, their remains settle onto the ocean floor and form layers of limestone and similar rock types. The carbon remains locked up there for millions to hundreds of millions of years, until it’s released again through volcanic activity.

This natural mechanism draws down at least half a billion metric tons of carbon dioxide annually. The problem is that society is steadily pumping out more than 35 billion tons every year. So the critical question is: Can we radically accelerate and scale up this process?

The idea of leveraging weathering to combat climate change isn’t new. A paper published in Nature proposed using silicates to capture carbon dioxide 30 years ago. Five years later, Exxon researcher Haroon Kheshgi suggested employing quicklime for the same purpose, and that same year Klaus Lackner, a pioneer in carbon removal, evaluated a variety of potential rock types and methods.

But enhanced weathering has gotten little attention in the decades since relative to more straightforward approaches like planting trees, altering agricultural practices or even building CO2-sucking machines. That’s largely because it’s hard to do, says Jennifer Wilcox, a chemical engineering professor who studies carbon capture at Worcester Polytechnic Institute in Massachusetts. Every approach has its particular challenges and trade-offs, but getting the right minerals at the right size to the right place under the right conditions is always a costly and complex undertaking.

More researchers, however, are starting to take a closer look at the technology as the importance of carbon removal grows and more studies conclude that there are ways to bring its costs in line with other approaches. If it’s cheap enough on a large scale, the hope is that corporate carbon offsets, public policies like carbon taxes, or sellable by-products from the process, such as the aggregate used in concrete, could create the necessary incentives for organizations to carry out these practices.

A handful of projects are now under way. Researchers in Iceland have been steadily piping a carbon dioxide solution captured from power plants or carbon removal machines into basalt formations deep underground, where the volcanic rock coverts it into stable carbonate minerals. The Leverhulme Centre for Climate Change Mitigation, in Sheffield, England, is running field trials at the University of Illinois at Urbana-Champaign to assess whether basalt rock dust added to corn and soy fields could act as both a fertilizer and a means of drawing down carbon dioxide.

Meanwhile, Gregory Dipple at the University of British Columbia, along with colleagues from other universities in Canada and Australia, is exploring various uses for the ground-down, highly reactive minerals produced as a by-product of nickel, diamond, and platinum mining. One idea is to simply lay them across a field, add water, and effectively till the slurry. They expect the so-called mine tailings to rapidly draw down and mineralize carbon dioxide from the air, forming a solid block that can be buried. Their models show it could eliminate the carbon footprint of certain mines, or even make the operations carbon negative.

“This is one of the great untapped opportunities in carbon dioxide removal,” says Roger Aines, head of the Carbon Initiative at Lawrence Livermore National Lab. He notes that a cubic kilometer of ultramafic rock, which contain high levels of magnesium, can absorb a billion tons of carbon dioxide.

“We mine rock on that scale all the time,” he says. “There’s nothing else that has that kind of scalability in all the solutions we have.”

In the wild

Project Vesta unveiled plans to move ahead with its pilot study in the Caribbean in May. That closely followed online payment company Stripe’s announcement that it would pre-pay the nonprofit to remove 3,333 tons of carbon dioxide for $75 per ton, as part of its commitment to spend at least $1 million annually on negative-emissions projects.

Project Vesta has secured local permission to begin conducting sampling at the beaches and intends to announce the location once it’s finalized approvals to move ahead with the experiment, says Tom Green, the executive director. He estimates the total cost for the project at around $1 million.

The central goal of the study, which will leave the second beach in its normal state as a control, is to begin addressing some of scientific unknowns that surround coastal enhanced weathering.

Research and lab simulations have found that waves will significantly accelerate the breakdown of olivine, and one paper concluded that carrying out this process across 2% of the world’s “most energetic shelf seas” could offset all annual human emissions.

But a major challenge is that the materials need to be finely ground to ensure that the vast majority of the carbon removal unfolds across years rather than decades. Some researchers have found that this would be so costly and energy intensive, and produce such significant emissions on its own, that the approach would not be viable. Still, others conclude it’ll remove significantly more carbon dioxide than it produces.

Project Vesta hopes to get scientists to the site to begin the actual experiment by the end of the year. After they spread the olivine across one of the beaches, they’ll closely monitor how rapidly the particles break down and wash away. They’ll also measure how acidity, carbon levels, and marine life shift in the cove, as well as how much those levels shift further from the beach and how conditions at the control site compare.

The experiment is likely to last a year or two. Ultimately, the team hopes to produce data that demonstrates how rapidly this process works, and how well we can capture and verify additional carbon dioxide uptake. All those findings can be used to refine scientific models.

Another area of concern, which they’ll also monitor closely, is https://www.frontiersin.org/articles/10.3389/fclim.2019.00007/full potential environmental side effects].

The minerals are effectively geological antacid, so they should reduce ocean acidification at least on very local levels, which may benefit some sensitive coastal species. But olivine can also contain trace amounts of iron, silicate, and other materials, which could stimulate the growth of certain types of algae and phytoplankton, and otherwise alter ecosystems and food chains in ways that could be difficult to predict, says Francesc Montserrat, a guest researcher in marine ecology at the University of Amsterdam and a scientific advisor to Project Vesta.