Direct Air Capture: How the fight against climate change will be won or lost

Fifteen years from now, when the Great Barrier Reef is a thing of the past, when downtown Atlantic City, Bangkok, Boston, Charleston, Dhaka, Galveston, Honolulu, Jakarta, Lagos, Manhattan, Miami, Mumbai, New Orleans, Newark, Rotterdam, San Francisco, Seattle, Tampa, and Venice relocate, and when Australia and California burn, everyone — from farmers to stock brokers, peasants to politicians– will be asking the same question: Are the machines working?

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Those machines will be sucking carbon out of the air and burying it deep in the ground or under the sea. We don’t know exactly where they will be, what they will look like, or even how well they will work. All we know is that we need them (Lackner et al 2013).

Reducing our carbon emissions, which humans have proved incapable of, is not enough now. Even reducing to zero emissions tomorrow is insufficient. We are too far gone in the wrong direction. What’s more, like a ship heading for the end of the world where the water falls off the edge, our foot is still on the accelerator. Slowing down is good, but insufficient to avert disaster; we must turn the ship around and head the other way. We need to not just reduce emissions, we need to reduce the amount of CO2 already in the atmosphere. That means negative emissions– sucking carbon out of the air.

Direct Air Capture vs Flue Capture; Sequestration vs Re-Use

Carbon capture from ambient air, also called Direct Air Capture (DAC), is different from conventional carbon capture at factory chimney flues (i.e. point source carbon capture). First, it’s a lot easier to capture carbon from flues because the CO2 is concentrated. Second, typically the goal of flue carbon capture is to minimize CO2 emissions and often to re-use the CO2 in a process that reduces the need for fossil fuels. If it is re-purposed, you’ve reduced CO2 emissions from fossil fuels, but the CO2 is still released into the atmosphere. This is a process to reduce emissions; it is not net-negative.

There are also plans to capture carbon, from the air or from flues, and use it in a variety of other industrial processes, from putting bubbles in soda to (wait for it)… extracting more oil. These plans are merely meant to reduce emissions and also to incentivize the private sector to capture carbon. But it’s not net-negative.

Feasibility

Back to direct air capture. Here’s the catch: we don’t know if we can do it at the scale needed. Fortunately, humans have been much better at finding technological solutions than political ones. There are more than a dozen pilot projects in Iceland, Switzerland, and elsewhere showing it can be done– on a very small scale. There are a host of questions, but the biggest challenge is sucking it out of the air in an efficient and cost-effective way.

Funding

Feasibility aside, there’s the question of how to pay for it. Suppose we wanted to capture and sequester 7 billion metric tons of CO2 annually, which is the IPCC goal by 2050. Currently we emit 43 billion. Early estimates are that it would cost $700 billion/year (at $100/ton) and require an enormous amount of energy, up to a 12% of annual worldwide energy use. But those are early estimates. Technology gets better and cheaper with time. The Center for Negative Carbon Emissions at Arizona State University thinks it can be done for $210 billion/yr (using $30/ton) and require only 1% of worldwide energy use.

For context, worldwide military spending is $1.8 trillion/yr (or $1,800 billion), nearly half of which is by the US. If the armies of the world ever wanted to save a city, let alone a village, they have the money to do it.

Ultimately, governments will have to pay for carbon capture and sequestration. There is no way to incentivize the private sector to bury a product rather than re-use it. In the near term, we can benefit from private sector carbon capture and re-use because, although it is not net-negative, it can incentivize research into DAC technology. And it does reduce emissions.

DAC on a meaningful level requires international coordination and, of course, cost sharing. The two most obvious models would be to apportion cost share based on current or past CO2 emissions.

Each nation will likely be up to its own to develop their own funding mechanism. A carbon tax is an obvious solution. If DAC costs $100/ton, that translates to 88 cents/gallon at the pump. Other fossil fuel uses would also have to be taxed as well. While this sounds affordable, there are two complicating factors: 1) we can’t just address the gallons of gas we are buying now; we have to address all the gas we have ever bought and all our parents have ever bought; and 2) carbon taxes are regressive, hitting the poor more than the rich (as a percentage of their income). There are ways around that, a subject for another blog post.

The enormity of the task means that technological innovations to lower the cost are critical. This should not be left to small policy initiatives like research grants and tax incentives. This requires the full weight of all the major governments and universities in the world. Progressive governments in Europe and California (where Democrats have super-majorities in both houses of the legislature) could and should embark on DAC projects immediately.

The Free Rider and Moral Hazard Problems

CO2 released anywhere in the world spreads everywhere, and DAC done anywhere reduces CO2 everywhere. This is both good and bad. It means that DAC can be done anywhere, allowing us to select the most expedient locations. For example, a DAC pilot study in Iceland uses clean geothermal energy to capture carbon and inject it into porous volcanic rocks.

But it also means there’s a potential free rider problem, where countries will shirk their obligations in the hopes that others will take care of it for them. One can imagine rogue nations that refuse to pay their fair share and free ride on the public service provided by other countries. The US, whose share would be large by any measure, is a candidate for such recalcitrant behavior. Public support for DAC could overcome this.

It is possible that Republicans would support DAC. The US Congress recently passed a $50/ton tax credit for DAC removal, the most ambitious such incentive in the world. Republican support, however, probably came from the associated $35/ton tax credit for carbon captured from the air and used for enhanced oil extraction. Regardless, Republicans could see DAC as an opportunity to extend fossil fuel use into the future. And therein lies the moral hazard problem. If we’re doing DAC, one could argue that we don’t need to reduce emissions as much. And if DAC became cheap and easy, fossil fuel use (aside from the spill risks and air quality impacts) could arguably continue.

But, like with a penny saved rather than earned, carbon not emitted is carbon you don’t have to capture and sequester. There are two more reasons why reducing emissions must still happen: 1) at the moment, it’s still cheaper to reduce CO2 emissions than to capture it; and 2) we are nearing the edge of the world, when it’s too late even to capture carbon.

Positive Feedback Loops

This brings us to the gremlins in the room– positive feedback loops. These are additional sources of global warming that are caused by the current global warming. They are force multipliers, accelerators, that can make global warming much worse very fast. It’s hard to predict when they will kick in. If they do, our job will become much much harder. We will lose ground, a lot more ground (read human suffering) before we win. They put victory in doubt.

Some positive feedback loops, such as increased water vapor in the air and dark seas and mountains exposed from melting ice and glaciers, have been accounted for in climate models. More pernicious are the more unpredictable “time bombs”, such as permafrost melt and massive wildfires.

Melting permafrost is the proverbial elephant of the gremlins in the room. Research suggests that rapid methane releases from melting permafrost may have been the final driver in runaway climate change that led to past mass extinction events, including the End-Permian Extinction in which 97% of all life on earth perished. This effect is already happening. NOAA recently reported that melting permafrost now contributes as much as net 0.6 billion tons of carbon (equivalent to 2.2 billion tons of CO2) to the atmosphere each year; “the feedback to accelerating climate change may already be underway.”

Forests are normally carbon sinks, taking in CO2. However, in 2006 Westerling et al warned that “forests of the western United States may become a source of increased atmospheric carbon dioxide rather than a sink, even under a relatively modest temperature-increase scenario.” Since then, wildfires have increased dramatically.

These positive feedback loops are like an increasing current threatening to pull the ship over the falls. If we are waiting for technology to save us, we may have waited too long.

Controlling the Climate

In the long run, Homo sapiens might eventually hopefully maybe win the climate battle and be able to capture and sequester enough carbon to return the earth’s atmosphere to normal conditions. But there will be suffering in the short-term, for the next two hundred years, thru sea level rise, heat waves, droughts, powerful hurricanes, and agricultural disruption. The poor will suffer most. Turning the climate around is like turning a cruise ship. There’s a lot of lag time between cause and effect. That’s why humans have found themselves in the current crisis. Only the scientists saw it coming. Nobody felt the impacts until now, and now it’s too late to avoid them. The same is true regarding corrective measures. A lot of sea level rise, caused by ice melt in Greenland and Antarctica, is already built into the system. It is coming and coming at an increasing and exponential rate. We may have to actually cool the planet beyond the recent historic level to stop it. And that may take 150 years. In the meantime, hundreds of coastal cities will go under water. This appears inevitable, even under the most optimistic scenarios.

The graphs below present the most wildly optimistic scenario, achieving the Paris goal’s peak emission in 2020 (this year), DAC of 7 billion tons of CO2 per year by 2050, plus optimistic net removal thru reforestation and new soil management practices, all of which help to get us to net-zero emissions by 2050, another Paris goal. After that, we remove more than we emit; we are net-negative, returning the earth to under 400 ppm.

It would be great to just use natural approaches to sequester carbon (e.g. reforestation and soil management). But the numbers just don’t add up fast enough. During past global warming events (e.g. the Paleocene Eocene Thermal Maximum), it took the earth’s natural processes tens of thousands of years to restore balance. We have put so much carbon up so fast thru industrial processes that we need the same kind of speed sucking it back in. Nevertheless, looking at the graph below, reduced carbon emissions are still the biggest player, followed by DAC and the natural processes. We need it all to the maximum extent possible as soon as possible.

But this wildly optimistic scenario still has us peaking at 510 ppm in 2050, high enough to hit 2.0 Celsius warming, which is perilously close to unleashing enough carbon and methane from permafrost and other positive feedback loops to launch us toward 3 or 4 or 5 C warming and create another mass extinction event  (which we know from the past the world will recover from, re-evolving new life forms, in a few million years).

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The graph of CO2 levels below is derived from the assumptions regarding CO2 emissions and removal above. This is a best case scenario.

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But suppose humanity gets past this. Successful implementation of carbon capture and sequestration would mean that Homo sapiens can control the earth’s climate. That brings with it a host of other questions. At what level do we set atmospheric CO2? Do we return to 300 ppm or lower? Who decides? Because carbon released or captured anywhere affects everywhere, who will police it? These are questions for our children, if they are fortunate.

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