Can carbon removal save us?
29 April 2019
Under the 2015 Paris climate accord, 195 countries committed to limit global warming to 2°C above pre-industrial levels. In November 2018, the Inter- governmental Panel on Climate Change (IPCC) published a report stating what needs to happen if we want to keep warming below 1.5°C. But as PETER WADHAMS points out, both aims have an embarrassing fact in common: they cannot be achieved simply by reducing carbon emissions. They require us to actually remove carbon dioxide from the atmosphere.
THE PARIS AUTHORS recognized the need for carbon removal, but didn’t suggest how to do it. The IPCC authors went further: they explicitly rejected the use of geoengineering methods to cool the atmosphere on the grounds that there may be unknowable side effects. This leaves direct removal of carbon as the only method available to bring net emissions to zero.
To survive climate change, we have to develop technology to perform a massive CO2 removal economically. Success would bring two benefits: Not only would the rate of warming slow, but if the CO2 level dropped to a level lower than today’s, we would return to a climate of the past. This would allow us the luxury of tackling the other myriad problems facing the world, from food insecurity to water shortages to overpopulation.
The world now emits 41 billion tons of carbon dioxide per year, and the amount is rising. The current level of carbon dioxide in the atmosphere is already high enough to bring about a warming of more than 2°C. What this means is that if we want to save the Paris Agreement—and we cannot reduce our emissions to zero— we must combine a significant emissions reduction with the physical removal of at least 20 billion tons of carbon dioxide from the atmosphere per year indefinitely.
Currently, the best proposed way to remove carbon dioxide is through direct air capture, which involves pumping air through a system that liquefies and stores the carbon dioxide or converts it into a substance that is either inert or useful. Enterprising researchers have already developed systems that work by passing air through anion-exchange resins that contain hydroxide or carbonate groups that, when dry, absorb carbon dioxide and release it when moist. The extracted carbon dioxide can then be compressed, stored in liquid form and deposited underground using carbon capture and storage technologies.
The usual immediate objection is to ask how we can cope with 20 billion tons of CO2 per year. One proposed solution is to convert it into artificial limestone and then crush it to form an aggregate. Every year the world uses tens of billions of tons of sand and aggregate in construction, especially concrete production, using vast amounts of energy to do so and depleting the environment of sand. This would be a use of CO2 where the magnitude of the demand matches that of the supply.
The challenge is to bring the cost of this process to below US$40 per ton of carbon removed, since this is the estimated cost to the planet of our emissions. At the moment, most methods cost more than $100 per ton, but there are dramatic developments with great promise under way. Three companies have already opened pilot plants: Global Thermostat (United States), Carbon Engineering (Canada) and Climeworks (Switzerland). Carbon Engineering, operating in Squamish, British Columbia, employs a complex process that uses solar power to cause absorbed CO2 to react with hydrogen to produce a biofuel that can replace fossil fuel.
But Climeworks is the trendsetter. After building a small plant that fed absorbed carbon dioxide into a greenhouse, it opened a small-scale commercial plant in Iceland aimed at removing carbon dioxide from the air and using water to pump it down into basalt rocks underground, harnessing Iceland’s abundant geothermal power as a source of energy. Here the carbon dioxide is literally turned to stone—it mineralizes rapidly because of the type of rock and the pressure. Once turned to stone, the carbon dioxide is out of the planet’s energy system for millions of years. This is an enormous breakthrough.
A compelling criticism of carbon removal is that it may discourage us from trying to reduce our carbon dioxide emission levels, shifting our focus to unproven “emit now, remove later” strategies. Even the IPCC talks about “overshoot” whereby the CO2 level is allowed to rise beyond a safe limit and is later brought back down (by unspecified means). It doesn’t help that as a global population, especially in the West, we are reluctant to give up the comforts and conveniences of a fossil fuel world. Education is needed to make people at all levels (including US presidents) realize that we cannot continue as we are.
Effective carbon dioxide removal operations will need to be in place very soon. We need to immediately assess which direct air capture method offers the best chance of success, and check out other gentler methods that have been proposed, such as afforestation on a gigantic scale, or methods involving marine CO2 absorption on algal mats.
If, as I suspect, a direct chemical method is all that will do the job in time, then we’ll need to develop the equipment, funding and logistics for extracting about 20 billion tons of carbon dioxide each year, indefinitely. If we can manage this, we can save our society and our children’s futures. After all, if carbon dioxide is the chief cause of climate change, its removal would be our salvation.
PETER WADHAMS is an oceanographer, glaciologist and professor of ocean physics in the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge, UK. His research focuses on sea ice and climate change processes in polar regions. His book about the loss of ice on Earth, A Farewell to Ice, was published in 2016.
WWF's position on carbon removal
WWF believes that relying heavily on CO2 removal to mitigate global warming is a high-risk undertaking because we still don’t fully understand the reliability, costs, benefits, impacts or risks of many carbon capture approaches.
For that reason, our position is that the world’s immediate priority should continue to be cutting greenhouse gas emissions rapidly and deeply, since cutting emissions faster reduces our future need for CO2 removal.
That said, WWF acknowledges that some CO2 removal will likely be needed to limit the global temperature rise to 1.5°C—both to cancel out hard-to- mitigate residual emissions and/or to reduce the atmospheric CO2 concentration in the event of temperature overshoot scenarios.
In that context, it’s important to understand that all CO2 removal approaches have potential trade-offs or limitations. To the extent that they are used, we recommend prioritizing approaches that permanently sequester CO2 in natural systems—especially approaches with proven benefits for people, nature and climate.
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