The limited case for direct air capture

Nascent tech that pulls CO2 from the atmosphere could "significantly" reduce the costs of fighting climate change, but achieving scale is hardly a sure thing and massive deployment would consume lots of energy, a new peer-reviewed study warns.

Why it matters: The paper in Nature Communications arrives amid increasing attention to direct air capture (DAC) and other negative emissions technologies. They're important because it looks pretty unlikely that nations will cut emissions enough to meet the goals of the Paris climate deal.

• The firm Carbon Engineering — whose backers include Bill Gates and oil giants Chevron and Occidental — recently announced plans for a big DAC plant in Texas.

What they found: According to the study, widespread deployment down the road would create a longer cushion to achieve steep emissions cuts.

• In one scenario they modeled for holding global temperature rise to 1.5°C, it pushes the horizon for achieving "net-zero" emissions back from 2050 to roughly 2070, which would be "compensated by larger negative emissions thereafter."

Threat level: If policymakers wrongly bet on large-scale deployment, it could lead to a global temperature "overshoot" of up to 0.8 °C. That's a lot, given that Paris aims to limit the total increase to 1.5°C–2°C above preindustrial levels.

• And large-scale deployment (think tens of thousands of big machines under one tech scenario), if even proven feasible would need to be really large, and that's not without consequences.

• In theory, a huge buildout would consume as much as a fourth (!) of global energy demand to power and heat the systems by 2100, the paper notes.

The bottom line: The paper warns that DAC should not be viewed as a crutch, but rather as complementary to emissions-cutting strategies.

• The authors recommend that policymakers speed up development and deployment, but "without easing near-term mitigation efforts" due to risks of the tech underperforming or failing.

Go deeper, via Carbon Brief: Direct CO2 capture machines could use ‘a quarter of global energy’ in 2100