Stopping Global Warming By Taming Acid Rain
Harvard's wily Center For The Environment has upstaged its geoengineering competitors in the race for the $25,000,000 CO2 reduction X-Prize offered inventors by Al Gore & Richard Branson of Virgin Airlines.
Electrochemical Acceleration of Chemical
Weathering as an Energetically Feasible Approach to Mitigating
Anthropogenic Climate Change
Kurt Zenz House, Christopher H. House, Daniel P. Schrag & Michael.J. Aziz
We describe an approach to CO2 capture and storage from the atmosphere that involves enhancing the solubility of CO2 in the ocean by a process equivalent to the natural silicate weathering reaction. HCl is electrochemically removed from the ocean and neutralized through reaction with silicate rocks.
The increase in ocean alkalinity resulting from the removal of HCl causes atmospheric CO2 to dissolve into the ocean where it will be stored primarily as HCO3− without further acidifying the ocean. On timescales of hundreds of years or longer, some of the additional alkalinity will likely lead to... permanent storage of the associated carbon, and the return of an equal amount of carbon to the atmosphere. Whereas the natural silicate weathering process is effected primarily by carbonic acid, the engineered process accelerates the weathering kinetics... replacing this weak acid with HCl.
...A range of efficiency scenarios indicates that the process should require 100–400 kJ of work per mol of CO2 captured... It may also be useful on a regional scale for protection of coral reefs from further ocean acidification. Application of this technology may involve neutralizing the alkaline solution that is coproduced with HCl with CO2 from a point source or from the atmosphere prior to being returned to the ocean.
Great Stuff if economically feasible ,so congratulations to the authors . But the deliberate timing of the announcement is disturbing. Having a new found candidate of their own will allow professional Greens and Carbon Traders to exploit the media circus following the Harvard workshop, allowing them to pretend the silliest alternatives, like orbital sunshades are paradigmatic , while ignoring the serious questions Paul Crutzen and other have raised as to the feasibility of low-mass aerosols as a means of saving polar ice.
"Engineering feasibility" and economic practicality are quite different mattters . Zenz and his coauthors ( Schrag n chairs the Harvard Center) are proposing an electrochemical scheme, in which salt water is hydrolyzed to make chlorine and sodium hydroxide. The chlorine yields hydrochloric acid, which can leach basic metal ions like magnesium out of rock far faster than the mild carbonic acid in rainwater, while the sodium hydroxide can be used to absorb CO2 from air and generate extra bicarbonate ions in the ocean, buffering its ability to absorb yet more CO2. Using these combined reactions, the authors estimate it will take roughly 10 to 40 thousand watt-seconds of power to harmlessly transfer a gram of carbon from the atmosphere to the ocean.
In other words, a watt of electrical power devoted to the Zenz idea could hopefully remove about two kilograms (~4.4 pounds) of carbon a year . Since mankind presently burns about a ton of carbon per capita annually, halting warming by stripping CO2 from the air and leaching rocks would require on the order of 500 watts times six and a half billion people's worth of dedicated electrical capacity. That is to say some 3 trillion watts.
As Californians know, a spare trillion watts is not always easy to come by- the authors would like it to be geothermal , but in present reality it equals a thousand nuclear plants or coal burning thermal power stations. At a dime per kilowatt hour ( given current fuel prices, allowance for inflation may be prudent), that's roughly a quarter trillion dollar monthly power bill , which would make the cost of offsetting all the carbon added to the atmosphere around a dollar a day per capita
A thousand dollars a year for a family of three may seem a comfortable figure considered as a fraction of the total US tax burden , but it remains rather dear for the billion or more people elsewhere who subsist on a dollar a day--or less. I cannot claim to have estimated the capital cost of this modest proposal, but its thermodynamically dictated power budget seems as macroeconomic as the rest of the Macroengineering schemes, from injecting sulfate aerosols into the stratosphere to paving suburbs with solar cells, and yes, the authors other carbon sequestration proposals.
On Nov.9, Science reported :
The degree of scientific uncertainty was clear throughout the 2-day meeting. In a discussion of existing models, climate modeler Ken Caldeira of the Carnegie Institution of Washington in Stanford, California, concluded that reducing the intensity of sunlight hitting Earth by about 2% could "markedly diminish" the massive warming effects of an atmosphere with a carbon dioxide content of 560 parts per million (ppm). (The current level is about 385 ppm.) But over lunch, researchers debated the analysis. "You know you can get some sea ice back," Caldeira said to David Battisti of the University of Washington, Seattle. "I don't know that," Battisti retorted, explaining that Caldeira's model assumed a so-called slab ocean, which does not include the heat circulation patterns that help determine the fate of polar ice.
And then there are the risks. Harvard paleoclimate scientist Peter Huybers told his colleagues during one session that understanding of the world's climate may not be sufficient to properly wield geoengineering tools. "We should be humble about how much we know about the climate system," Huybers said.
Most of the discussion focused on whether to jump-start what has been an anemic research agenda with no public financing. Some participants said that they were spurred into action by a paper that appeared in Climatic Change last year, in which Nobelist Paul Crutzen called for geoengineering research (Science, 20 October 2006, p. 401). Others were swayed more recently. Just 2 weeks ago, modeler Raymond Pierrehumbert of the University of Chicago in Illinois, writing on the RealClimate blog, compared discussing geoengineering to "having a shiny new toy" and told climate scientists to "get back to the serious business of trying to figure out how to economically reduce global CO2 emissions." At the meeting, however, Pierrehumbert urged scientists to study the problem as a supplement to cutting greenhouse gas emissions, although he called for a 10-year moratorium on any geoengineering. "To the extent I've changed my mind a little bit," Pierrehumbert explained to Science, the reason is the ease with which countries could embark on geoengineering.
Harvard climate researcher James Anderson told the group that the arctic ice was "holding on by a thread" and that more carbon emissions could tip the balance. The delicacy of the system, he said "convinced me of the need for research into geoengineering," Anderson said. And 5 years ago? "I would have said it's a very inappropriate solution to the problem."