Tuesday, April 5, 2016

Can We Reduce Carbon Emissions Enough to Meet Targets or Do We need Technology to Extract It Directly?

The suddenly urgent quest to remove carbon dioxide from the air (Chris Mooney, The Washington Post, Feb.26, 2016)

Also discussed here: Four ways to suck carbon out of thin air (Tim Meko, The Washington Post, Feb. 27, 2016)

Today we review an article that looks at the pros and cons of directly removing carbon from the air, in addition to the various plans to reduce emissions, which will be needed if the world is going to meet the goals (but not action plans) agreed to at the recent COP21 climate conference in Paris. Four approaches are described: Direct air capture, Bioenergy combined with carbon capture and storage, Afforestation and Enhanced weathering. While each can extract some carbon, the question remains if that is enough to meet the challenge which, in simple terms, means comparing the CO2 emissions of 17 tons/year/person (in the USA) with the extraction of a ton/day promised by technology. No question that something is needed in addition to the very modest targets that many countries are planning to reduce emissions at source. No surprise either that pricing carbon use is seen as essential. direct air capture  

Key Quotes:

 “the goals set at last year’s Paris accord on climate change, of keeping the planet’s warming “well below” 2 degrees Celsius, may not be achievable unless such technology comes to fruition.”

 “If you want to balance the books at this point, I don’t think you have a choice but to pull CO2 back that has already made it out…Or is about to make it out, because we are not overnight shutting down all the coal plants.”

“scientists have roughly calculated the remaining carbon “budget” for how much we can emit while still keeping below a 2-degree increase. And it’s extremely tight – well under 1,000 additional gigatons (or billion tons) of carbon dioxide. The world emits about 32 gigatons annually from energy use alone.”

Four ways to extract carbon from air:
  • Direct air capture …Carbon dioxide is pulled out of ambient air using absorptive substances that selectively bind to CO2. A company called Carbon Engineering uses fans to pull air across an absorbant membrane. There, CO2 is converted into a carbonate solution, which can be processed to trap the carbon.
  • Bioenergy combined with carbon capture and storage (BECCS)..Trees or other forms of biomass are burned in power plants and replanted. Power plants capture, compress and send carbon dioxide to sequestration sites, where it is buried or used for enhanced oil recovery.
  • Afforestation …Trees are planted in an area where a forest does not exist. Trees and vegetation consume carbon dioxide as they grow.
  • Enhanced weathering ..Slightly acidic rain falls on silicate rocks and they slowly break down to a carbonate solution. The carbon in the rain eventually winds up embedded in limestone rocks.
“I’m skeptical there is a technology that will cheaply capture CO2 at 400 parts per million when it’s expensive to do at 400,000 parts per million in a smokestack… It’s tougher thermodynamically. Carbon dioxide in air is a thousand times less abundant.”

 “simply planting huge amounts of trees where they currently do not exist, faces a similar hurdle. There’s no doubt more trees means less carbon dioxide in the atmosphere. Yet once again, vast areas could be required — and in the future, people will need even more land to grow food than at present.”

 “With all these technologies and ideas, then, the question becomes how to lower the cost and when the world will truly start investing. A boon to all of them, of course, would be setting a global (or for the U.S., national) price on carbon, thus making its removal more valuable.”

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