New XPrize Accelerates the Fight Against Climate Change

XPrize Carbon Removal aims to sequester 10 gigatons of CO2 per year by 2050

The XPrize Foundation recently announced the largest prize in its history. The foundation partnered with Elon Musk and the Musk Foundation to offer $100M for innovations designed to reduce carbon dioxide in the air and oceans. Registration for XPrize Carbon Removal begins on Earth Day 2021. The contest aims to spur innovation, raise awareness, and accelerate the development of new technologies and ideas. Teams will have just four years to obtain measurable results, but the timeline is tight for a reason. The effects of climate change are already being felt around the world. The question is whether the XPrize will successfully change the trajectory of climate change when so many other endeavors have stalled.

Carbon dioxide is a potent greenhouse gas and major contributor to climate change. Reaching carbon neutrality (where the amount of carbon emitted is exactly offset by the amount removed through natural or manmade processes) is not enough. In order to avoid the worst effects of climate change, we need to sequester 6 gigatons of carbon dioxide per year by 2030 and 10 gigatons per year by 2050. For that reason, XPrize Carbon Removal focuses on solutions that will actively remove carbon dioxide from the air and water. Teams will need to demonstrate that their prototypes can remove 1 ton of carbon dioxide per day with the ability to economically scale up to gigaton levels. The winning solution will be able to sequester carbon over a long period, ideally more than 100 years.

The idea of removing carbon dioxide (CO2) from the atmosphere to mitigate the effects of climate change is nothing new. Research teams and businesses around the world are already investigating carbon dioxide removal methods, and entrants to the contest could make use of existing technology. Here are just some of the ideas we might see vying for the top prize.

Enhanced Weathering

Weathering is a naturally occurring process which involves the physical and chemical alteration of rocks and minerals. Rocks rich in olivine, a magnesium-iron silicate, react with carbon dioxide in the air to form bicarbonate which is dissolved in groundwater and ultimately stored in the oceans. Enhanced weathering accelerates this process through human intervention, usually by grinding the rock to a very fine powder which is then applied to croplands or forests. A 2018 study estimated that enhanced weathering could remove from 4.9 to 95 gigatons of carbon dioxide per year. The wide range is due to the different rock types examined by the study, but even near the lower end of the range, this methodology could fulfill the XPrize requirements.

In addition to the formation of bicarbonate ions, rock dust also removes CO2 from the atmosphere by enhancing the productivity of agricultural lands by acting as a natural fertilizer. This could help to encourage the application of rock dust in poor areas unable to afford commercial fertilizers.

Enhanced weathering is limited by the availability of olivine-bearing rocks. Transporting large amounts of heavy rock dust over long distances would add carbon dioxide to the atmosphere through the burning of fossil fuels. The chemical reactions involved are most effective in warm, moist climates, which limits the effective extent of application to the tropics. However, rock dust can also be applied directly to the oceans where it may also help to mitigate ocean acidification. The cost ranges anywhere from $60 to $200 per ton of CO2 mainly due to the expense of milling the rock and transporting it to the application site. However, these costs could be mitigated by using waste rock from industrial facilities or locally sourced quarries.

Rock dust is gaining attention as a carbon reduction mechanism due to its simplicity and cost. Remineralize the Earth is a non-profit which promotes mineralization to restore soils and forests, produce more nutritious food, and remove excess CO2 from the atmosphere. For-profit companies — such as the Carbon Farm Project started by the Jersey Hemp Company in the UK — have already proven the use of rock dust to be economic when used in conjunction with sustainable agricultural practices.

Afforestation

Afforestation is the planting of forests where none existed previously. Trees draw carbon dioxide out of the air and convert it into sugars through photosynthesis. The more trees we plant, the more carbon dioxide we can remove from the atmosphere. It’s an all-natural, low-cost carbon removal system. However, the world is losing forest lands at an alarming rate. According to the Food and Agricultural Organization of the United Nations, primary forests have declined by 80 million hectares since 1990, mainly due to agricultural expansion.

The Great Green Wall project has the ambitious goal of planting new trees along an 8,000km section of the Sahel region in northern Africa in order to fight desertification and improve the lives of millions of people living in the region. Started in 2007, the project has already completed more than 15% of its goal. By 2030, the project expects to restore 100 million hectares of currently degraded land while sequestering 250 million tons of carbon in the process.

Afforestation is cost competitive. A 2013 study in Canada estimated the cost of carbon dioxide removal through afforestation at $3 to $12 per ton of CO2. The US Forest Service estimated the cost at $14 to $40 per ton of CO2.

While planting more trees seems like an easy solution, the reality is more complicated. Currently, newly planted trees do not offset the rate of deforestation. Forests are also victims of climate change as much as they are touted as a solution. Drought and rising temperatures are stressing forests around the globe and may limit where new trees can be planted. When forests burn, such as during the bushfires in Australia last year, carbon dioxide and other pollutants are released into the air.

Underground Injection

The ground beneath our feet is already the largest reservoir of carbon on the planet. Carbon is stored underground in rocks such as limestone and in oil and gas deposits. Carbon capture and storage makes use of these natural reservoirs by capturing carbon dioxide from smokestacks and injecting it underground. Once in storage, the carbon dioxide can react with the surrounding rock forming solid minerals such as calcite. In other cases, the CO2 is kept underground (either as a gas or dissolved in fluids) by the impermeable rocks above it.

On a human timescale, this method of carbon sequestration is as close to permanent as it gets. By taking advantage of a concentrated source of carbon (i.e. smokestacks), the process is more efficient than trying to remove carbon dioxide from the air where it is more dilute. This also allows the carbon dioxide to be removed before it can wreak havoc in the atmosphere.

The proximity issue is also one of its biggest drawbacks, too. In order for underground injection to be effective, the storage location needs to be close to the source of emissions. Power plants and factories usually aren’t constructed with carbon capture in mind. It can also be expensive. The CarbFix project in Iceland costs an estimated $49 per ton of CO2, but injecting into depleted oil and gas reservoirs is less costly at $5 to $15 per ton of CO2. But the biggest downside to underground injection as far as the XPrize is concerned is that it doesn’t remove carbon dioxide that’s already in the atmosphere. This is more of a carbon neutral approach than a carbon deficit approach (as currently implemented).

There are places where underground injection works well and the results are tantalizing. Petra Nova Carbon Capture in the US and Boundary Dam CCS in Canada both power generation plants using full-scale underground injection to offset their carbon dioxide emissions. Petra Nova is the largest carbon capture facility in the world. In Iceland, carbon dioxide is dissolved into “fizzy water” before being injected into volcanic reservoirs. The high geothermal gradient (that means the ground is really hot) helps to quickly convert the CO2 into calcite — 95% of it is mineralized after two years underground.

Direct Air Capture

It begs the question then: can’t we just pull carbon dioxide directly out of the air? The answer is yes, but it’s neither easy nor efficient (yet). For all the discussion of rising CO2 levels, it’s important to remember that in absolute terms, it makes up a very small percentage of the atmosphere, only 0.0407%. That makes it very difficult to pull CO2 directly from the atmosphere, but it is possible.

Most direct air capture methods use sorbents which are catalysts that can be used repeatedly to capture CO2. The resulting stream of CO2 can then be sequestered (through underground storage, for example) or used in manufacturing, although the latter may or may not serve as a long-term sequestration solution.

The big advantage of direct air capture is that it can be done anywhere. In fact, many small direct air capture plants might work better than a few larger ones. The biggest disadvantage is the cost. At present, the cost of direct air capture ranges from $250 to $600 per ton of CO2. However, the technology is only in its infancy, and the cost is likely to come down as it’s further developed. Direct air capture can also consume large amounts of water depending on the sorbent used, which adds to its cost and environmental impact.

These are just some of the methods we might see from entrants in the XPrize Carbon Capture. In practice, reversing climate change will likely require multiple approaches working in tandem. What is cost-effective and practical in one part of the world, may not work elsewhere. Global solutions are required.

Geoscientist, runner, and writer. I will never stop being curious about the world.

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