Commentary: Cutting carbon emissions isn’t enough

With carbon dioxide emissions continuing to grow, it’s becoming obvious that the world is incapable of abandoning fossil fuels quickly enough to avoid some of the worst impacts of climate change. Even after most nations made pledges as part of the 2015 Paris agreement, CO₂ emissions from fossil energy sources and cement manufacturing have risen. Last year’s figure of 37 gigatons was 2.7% higher than in 2017.

Some studies say that, at current rates, in as little as 10 years global emissions may blow us past the Paris accord’s goal—a 1.5 °C increase in the average world temperature since the dawn of the industrial era. In a 2018 report , the United Nations’s Intergovernmental Panel on Climate Change writes that to have a 66% chance of staying “well below” a 2 °C increase, humankind should spew no more than about 800 gigatons of CO₂. Achieving that will require CO₂ emissions be brought to zero as early as mid century. Some sources, such as air travel and agriculture, will be extremely difficult to decarbonize by then.

Enter negative-emissions technologies. As reviewed earlier this year in a National Academies of Sciences, Engineering, and Medicine report, there are many ways to extract CO₂ from the atmosphere. Replanting trees where they once grew or planting them in new areas is the simplest, though that alone won’t solve the climate crisis, nor will any other single measure. A related option is to grow trees and crops to extract atmospheric carbon and then to burn them for energy, with the emitted CO₂ captured and stored in geological formations. There are various techniques to accelerate the natural process of rock weathering, such as crushing and spreading basaltic or other reactive materials on soils, to expose more surface area for CO₂ absorption. Improved farming practices can greatly enhance soil’s carbon uptake.

There is also direct-air capture (DAC), which involves blowing huge volumes of air past contactors that contain compounds with an affinity for CO₂. Those chemicals are then heated to release pure CO₂, which can be stored in geological formations. Considered quixotic until a few years ago, the process is now, with some irony, attracting attention from the petroleum industry, albeit not entirely for altruistic reasons. Oil producers routinely use CO₂ to help force oil out of mature reservoirs, a process known as enhanced oil recovery. Within the last year, three US oil producers have invested substantial undisclosed sums in the two North American companies that are building DAC systems.

Making negative emissions happen at the needed scale and degree of urgency will require vastly enhanced R&D investments to mature nascent technologies. The National Academies report notes how an estimated $22 billion in federal R&D in renewable energy over 35 years has paid off handsomely by lowering utility-scale solar- and wind-energy costs to levels that make renewable energy competitive with fossil-fuel electricity generation.

But making negative-emissions technologies a reality will require more than R&D. It will take government loan guarantees and tax credits as well as early-stage and venture capital. It will take millions of square kilometers of arable land for growing trees or biomass, and it will require payments to farmers to reforest their acreage. To maximize its potential, DAC will require vast amounts of new renewable energy.

Most of all, governments will need to put a price on CO₂ emissions. The National Academies report says that as much as 1 gigaton of CO₂ per year in the US and 10 gigatons per year globally could potentially be extracted using currently available technologies for a cost of $100 per ton or less. (No estimate was given for DAC because the report authors deemed it not ready for prime time.) One need only look at the experience of clean coal to see the need for a carbon tax or an equivalent. Although technology has long existed to scrub CO₂ from the flues of coal- and gas-burning plants, it’s far too costly to be deployed in the absence of a sufficient carbon price or through regulation.

The US has a clear moral obligation to take the lead on negative emissions. Sadly, that won’t be happening under the current administration. The White House boasts of declines in US emissions during recent years. And indeed, US energy-related CO₂ output has been on a downward trajectory since its peak in 2007, largely due to natural gas supplanting coal in power generation. Yet despite China and India leading the world in emissions growth, the US remains the second-largest emitter, and at 16.2 tons per person, it continues to spew the greenhouse gas at more than twice China’s per capita rate. Since the Industrial Revolution, the US has been responsible for a full quarter of global CO₂ emissions.

Last year the Republican-controlled Congress took a small step to encourage carbon capture and storage with passage of the 45Q tax measure, which provides a credit of $35 per ton of CO₂ captured for use in enhanced oil recovery, carbonated drinks, and other industrial processes, and $50 per ton for CO₂ captured and stored underground. It’s a start, although the amount is well below the price that will be needed to encourage wide-scale capture and storage. Global Thermostat, a DAC company that in June announced a joint development agreement with ExxonMobil, claims its process can capture CO₂ for $100 per ton, but it has yet to demonstrate that in a commercial setting. The sole capture system that’s been sold for small applications is made by the Swiss company Climeworks, which puts its cost at $600 a ton.

Some have argued that pursuing negative emissions presents a moral hazard : that relying on CO₂ removal options would rationalize inaction on emissions cuts. Now, however, it’s clear that both slashing emissions and extracting carbon will be required. As more than one climate scientist has told me, the moral-hazard argument against negative emissions is itself a moral hazard.