The National Academies of Sciences, Engineering and Medicine is looking into another controversial tactic to fight climate change.

This time, it's carbon dioxide removal and sequestration.

The term encompasses several techniques that pull greenhouse gases out of the atmosphere and keep them from going back, thereby reducing warming. And scientists say the world needs to figure out what works and when to use it.

“Can we pull it out again and stick it someplace where it won't do any harm?” asked Princeton University professor Stephen Pacala, who is chairing the National Academies committee for carbon dioxide removal and sequestration. “This is a tall order, because we've put a lot of CO2 in the atmosphere.”

Scientists are concerned about the unintended consequences of nurturing ecosystems to breathe in more carbon dioxide or building machines that react with greenhouse gases and sequester them. There isn't much research out there on the economics and effectiveness of these strategies.

Many activists are worried that carbon dioxide removal technologies will detract from climate change mitigation efforts, that they will cost too much, or that nations will see them as a license to keep polluting.

“The No. 1 outcome we wanted to make clear is there is no substitute for mitigation and adaptation,” Waleed Abdalati, a professor at the University of Colorado, Boulder, said at a public meeting of the National Academies yesterday in Washington, D.C.

The pace of humanity's greenhouse gas emissions output continues to grow, and even with international targets for curbing emissions, many scientists project that the world will overshoot a target of limiting global warming to 2 degrees Celsius.

Keeping warming in check would require methods that result in negative greenhouse gas emissions, whether using air capture systems or bioenergy coupled with carbon capture and sequestration setups (Climatewire, March 24).

This poses an immense engineering challenge to counteract humanity's influence on the planet, so the National Academies is chalking out a plan that could bridge the divide between where the technology stands and where it needs to go (Climatewire, May 19).

“It took the entire fossil fuel infrastructure of the world to put it all there, and if you're going to do it at scale, you're going to need a lot of stuff, a lot of people, and it's going to be expensive,” said Pacala. “So you want to figure a way to minimize the energy, materials, consumption and lower the costs.”

DOE spending $2.75M

The new research is supported by the Department of Energy, the U.S. Geological Survey, the National Oceanic and Atmospheric Administration, U.S. EPA and the V. Kann Rasmussen Foundation.

The work on carbon removal builds on past analyses at the National Academies examining contentious geoengineering techniques, like seeding oceans with iron to spur the growth of organisms that take up carbon dioxide.

Removing carbon dioxide gets at the root of the climate change problem, unlike geoengineering, which masks it. But there are some unique challenges.

Carbon dioxide itself is not a very reactive molecule, so many proposals for sucking it up require an energy input. This means careful life-cycle accounting to make sure that more carbon dioxide comes out of the atmosphere in deploying these systems than goes in.

In addition, carbon dioxide is extremely dilute in the atmosphere, with concentrations peaking around 400 parts per million, so a machine that scrubs it out of the atmosphere would have to go through an immense amount of air to make a meaningful dent in rising temperatures.

DOE is taking a stab at this with two projects launched last year: a $1.5 million system in Canada that uses a hydroxide solution to react with carbon dioxide and a $1.25 million project at Ohio State University that uses membranes to separate carbon dioxide from the air.

DOE was allocated $250,000 to look at the commercial viability of carbon dioxide removal strategies, including participating in the National Academies study.

However, DOE's Office of Fossil Energy took a hit in the White House budget proposal released this week, with funding cut from $668 million to $280 million. That could limit further funding for pilot-scale projects.

“We are going through some transitions, but there is still CCUS [carbon capture utilization and storage] activities in that budget,” said John Litynski, the carbon capture program manager at DOE's fossil energy office. “We are shifting our efforts to look at more early-stage R&D in our program.”

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at