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Climate Change: Hot Debate over Green Concrete


Climate savior or potential green-washer? Los Gatos, Calif-based startup Calera Corp has a bold idea to do something concrete about climate change—literally. With venture funding from Vinod Khosla, the company plans to take carbon dioxide emitted by coal-fired powerplants, and combine it with seawater to make a ‘green’ concrete. The process is similar to the formation of coral reefs, the company says. It even arranged for an exhibit showing the process at the California Academy of Sciences.

Not so fast, says Ken Caldeira, climate scientist at the Carnegie Institution of Washington at Stanford University. “Their claim that they can put CO2 in sea water and create minerals makes no sense to me at all. When coral does make reefs, Caldeira points out, CO2 is

actually released to the atmosphere. Making concrete-like minerals through the process “is backwards to the chemistry the rest of the world is accustomed to,” Caldeira says.

So in an email message on March 22, Caldeira took on Calera, company founder and CEO Brent Constantz (also an earth sciences professor at Stanford), and the California Academy of Sciences.

He wrote: “From the publicly available information it seems that Calera's process goes in the wrong direction and will tend to increase and not decrease atmospheric CO2 content. Furthermore, when I raised these concerns to Calera, they would not respond openly to my critique, asking me instead to sign a non-disclosure agreement.”

“I call upon the California Academy of Sciences to withdraw the Calera exhibit until such time that Calera demonstrates (i) that its process does not remove cations from the ocean in a way that will ultimately drive a CO2 flux from the ocean to the atmosphere that exceeds the amount of fossil fuel stored in the carbonate mineral and (ii) that its process does not acidify the ocean.”

“I am not sure whether Calera is ignorant or intentionally misleading, or whether they actually have a basis for their claims. If they do have a basis for their claims they should state them now. If not, the California Academy of Sciences should remove their exhibit from the museum…. I believe Calera and the Academy of Sciences are now misinforming schoolchildren, and that is not a good thing to do.”

The Academy promptly responded by saying “we are looking into the issue, and if we have incorrect information on display, we will certainly remove it.”

Calera’s accused CEO, Brent Constantz, wasn’t so accommodating. In an angry email response, he accused Caldeira of trying to force his company to license a patent that Caldeira holds. “Based on this thinly covered, transparent attempt to disguise a need to get information for a greedy hope of a royalty stream as a concern for schoolchildren, I would question your personal imtegrity (sic), and tell you Callera (sic) wants nothing to do with you [and] your bogus science,” Constantz wrote.

Ouch. “Instead of providing facts, they launched an ad hominem attack on me,” Caldeira says. “Maybe they have an explanation. Maybe they have figured out some chemistry that’s magical I don’t know about, But they should come back explaining that, and not attacking me.”

What’s really going on? Caldeira suspects that “there is still a bubble in the clean tech world. The bubble may have popped in the rest of the economy, but it looks to me that, in this segment, there still a bubble and things that not seem to make much sense are attracting venture capital funding.”

As for Constantz, he downplayed the tiff in an email reply to BusinessWeek: "I think this has already blown over, as many people have forwarded Calera's published patent applications and water discharge permits to Caldeira, who apparently was unaware of all the detailed public information about our process. Needless to say, Caldeira has no leg to stand on, as our process has been in the public domain since last year, and the detailed information about inputs and outputs are in public records related to operating permits as well as the published patent applications."

"The chairman of our Scientific Advisory Board is willing to write a response to Caldeira's ungrounded claims - but we can't decide if it's really worthy of a response. I guess you have to ask yourself what the guy's motivation has been on attacking Calera - I certainly have no idea."


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