If we care about our earth (and the readers here are most likely to) the story is quite simple: We emit 40 billion tons of carbon annually, and little is being done to reduce it. There is also not much likelihood of any action from our leaders, given the Senate vote on the Green New Deal and President Trump's well-known views on the subject . So how do we get rid of the carbon about to turn earth into a living hell? Deadlines have been clearly laid down by experts.
The October 2018 IPCC report on limiting global warming to 1.5C above preindustrial levels notes human-caused CO2 emissions would have to achieve 'net-zero' by 2050. According to the report, this would necessitate 'far-reaching transitions' not just in how energy is used and produced but also in the use of Negative Emissions Technologies (NETs) such as carbon recapture from the air. We have to stabilize earth or eventually a self-reinforcing feedback loop will lead to uncontrollable warming and a "Hothouse Earth" without any means of reducing earth temperatures.
Scientists
assessing NETs find that restricting global warming to 1.5C requires
large-scale deployment of NETs; in fact, a major national effort.
Moreover, any single NET is unlikely to be sustainably adequate, rather
multiple NETs each on a more modest scale is the most effective
scenario. A comprehensive analysis is therefore both illustrative and illuminating.
Direct air carbon capture and storage (DACCS) is an
enticing prospect until one examines the costs. Scientific scenarios
project DACCS capacity to remove 10-15 billion tons of CO2 per year by century's end.
Optimists up it to 35-40 billion tons solving the CO2 problem in one
fell swoop. Not so, say those who have examined costs.
A group from the Mercatur Research Institute on Global Commons and Climate Change
and Humboldt University of Berlin and in particular Sabine Fuss have
examined costs reporting on different NETs in Environmental
Research Letters (ERL, June 2018). They put the cost at $100-300 per
ton
for DACCS and estimate sustainable removal at 0.5 - 5.0 GtCO2 per year
-- a Gt is approximately a billion tons. The upper level would still
cost $500 billion to $1.5 billion according to them.
The
other major problem with DACCS is the sheer energy required. Removing a
million tons a year would consume 300-500 MW according to Jennifer Wilcox of Worcester Polytechnic. The power needs to be clean energy
for a coal-fired plant would generate more CO2 than would be extracted.
Climeworks is a company based in Switzerland that has developed a DACCS process. Its
pilot plant in Hellisheidi,
Iceland, is using geothermal energy to remove CO2 from the air and
store it in basalt. They have also announced a commercial scale venture
in Zurich, Switzerland.
In
addition to active air capture as described, there is a passive
approach. An Arizona State University professor has developed a resin that
when dry absorbs CO2 from the air, relinquishing it when
immersed in water. The team envisions artificial trees made from the
resin each capable of capturing a daily ton of CO2.
As
an addendum to afforestation one might note an investment by Apple on a
project by Conservation International to restore and protect 27,000
acres of mangroves in Columbia. This will capture a million tons of CO2 annually as 'blue' carbon stored in coastal marshlands and mangroves can be up to ten times more dense than in forests.
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