Direct Removal Of CO2 Impractical
According to a new report from the American Physical Society, Direct Air Capture (DAC) of CO2 using chemicals is not a viable solution for removing greenhouse gases from Earth's atmosphere. DAC involves a system in which ambient air flows over a chemical sorbent that selectively removes the CO2. It is one of a small number of strategies that advocates say could allow the reduction of atmospheric CO2. Prepared for the APS Panel on Public Affairs (POPA), a collection of scientific experts, the report claims to be a technology assessment containing no policy or funding recommendations. Unfortunately for its advocates, the APS report finds the approach untenable for technical reasons.
The American Physical Society was founded in 1899, with a mission of advancing and diffusing the knowledge of physics. APS is now the nation’s leading organization of research physicists with more than 48,000 members in academia, national laboratories, and industry. POPA routinely produces reports on timely topics to promote informed debate about relevant issue, including energy and the environment. The 100+ page report was quietly released on April 28, 2011, and gives as its purpose the following.
The goal of this report is to enable scientifically literate non-specialists to think independently about DAC, whether they are primarily interested in advancements in DAC technology or in placing DAC in a policy context. Throughout, the report seeks to demystify, to explain unfamiliar vocabulary, and to work through representative calculations.
The assessment is the outcome of a two-year study conducted by a 13-member committee whose members work in industry, academia, and national and government laboratories. It concludes that DAC would play a very limited role in a coherent CO2 mitigation strategy for many decades. It lists as its key messages:
- DAC is not currently an economically viable approach to mitigating climate change.
- In a world that still has centralized sources of carbon emissions, any future deployment that relies on low-carbon energy sources for powering DAC would usually be less cost-effective than simply using the low-carbon energy to displace those centralized carbon sources. Thus, coherent CO2 mitigation postpones deployment of DAC until large, centralized CO2 sources have been nearly eliminated on a global scale.
- DAC may have a role to play eventually in countering emissions from some decentralized emissions of CO2, such as from buildings and vehicles (ships, planes) that prove expensive to reduce by other means.
- Given the large uncertainties in estimating the cost of DAC, century-scale economic models of global CO2 emissions that feature ―overshoot trajectories and rely on DAC should be viewed with extreme caution.
- High-carbon energy sources are not viable options for powering DAC systems, because their CO2 emissions may exceed the CO2 captured.
- The storage part of CO2 capture and storage (CCS) must be inexpensive and feasible at huge scale for DAC to be economically viable.
- This report provides no support for arguments in favor of delay in dealing with climate change that are based on the availability of DAC as a compensating strategy.
Reported in an article on ScienceDaily, study co-chair Robert Socolow, a professor of mechanical and aerospace engineering at Princeton University, commented, “we humans should not kid ourselves that we can pour all the carbon dioxide we wish into the atmosphere right now and pull it out later at little cost.”
According to the report, direct air capture could at best be deployed slowly. On its own, DAC might be able to reduce the CO2 concentration by 50 parts per million (ppm) over a century, a relatively small amount. Moreover, DAC is not suited to the task of reacting quickly to an abrupt climate emergency. Climate alarmists looking for a magic bullet solution to the perceived problem of climate change are barking up the wrong tree.
“We ought to be developing plans to bring to an end the carbon dioxide emissions at every coal and natural gas power plant on the planet,” Socolow continued. Beyond using electricity more efficiently, options are to modify plants so their emissions are kept from the atmosphere or to shut them down entirely and replace them with low-carbon alternatives.
Imagine thousands of chemical air processors, each more than 30 km long.
Even though climate scientists have not been able to identify all of the factors involved in climate regulation, or even develop trustworthy values for the ones they do know about, some eco-activists are proposing that we actively try to alter Earth's climate. There have been numerous calls for this type of post emission solution in recent years, part of the nascent field of geoengineering.
Indeed, after international negotiators at a recent UN climate conference repeated the demand that global warming this century be limited to no more than 2˚C, a report sponsored by the Canadian government found this goal unrealistic. The most extreme scenario studied called for the use of unproven and highly questionable geoengineering carbon sequestering technology. What level of effort would be involved to implement such a system? Here is an example culled from the report that was spotted by one of our readers:
The physical scale of the air contactor in any DAC system is a formidable challenge. A contactor through which air flows at two meters per second and that removes half of the CO2 from the contacted air will capture about 20 tons of CO2 per year for each square meter of frontal area. A 1,000-megawatt coal power plant emits about 6 million metric tons of CO2 per year, and to remove CO2 from the atmosphere as fast as this coal plant emits CO2, such a system would have a total length of about 30 kilometers if it were based on structures 10-meters high. Large quantities of construction materials and chemicals would be required.
To put this in perspective, simulations done by researchers at Carnegie Mellon University in 2010, suggest that for every 100 billion tons of carbon removed from the atmosphere, average global temperatures would drop 0.16° C (0.28° F). Of course, these projections, estimates and concerns com with a number of big ifs.
Terraforming, it's not just for alien worlds anymore.
These concerns only matter if anthropogenic CO2emissions are going to rise as predicted, if they will have the effect the computer models say they will, and if that turns out to be a bad thing after all. Then maybe, just maybe, we should allow some of the environmental loonies to start messing with the atmosphere we all live in and breath. Or not. Such muzzy-headed thinking has always bothered me.
If you assume that we humans are messing up the planet so badly by accident, then letting some group of wild-eyed mad scientist types modify the climate on purpose seems like a real invitation to disaster. Given that we cannot predict what Earth's climate will do in the future with any certainty, how do we know what tweaks to make to the atmosphere to yield the desired outcome. For that matter, who gets to say what the desired state of nature should be? I think we should wait a bit longer to see what develops before filling the world with ten meter high 30 kilometer long chemical plants—one for each coal fired power plant on Earth—in an attempt to remanufacture the atmosphere.
Be safe, enjoy the interglacial and stay skeptical.