Posted by Jeff Condon on July 31, 2010
I’ve put in a few days time now studying carbon sequesterization in limestone. This morning I’ve run several calculations based on raw data dug up in Al Gore’s house – a.k.a. the internet. Joking aside, I flatly disagree with the IPCC two hundred year shelf life of CO2. It makes zero sense to me, and of course basic numbers don’t agree. My hypothesis is that limestone production is a strong feedback mechanism to CO2 production. It’s nearly a self proving result because of the very low concentration of plant food in the atmosphere for so many millions of years, but most don’t seem to consider that as evidence.
This paper is an estimate of limestone sedimentation rates across the ocean based on biological origin, other papers provide similar numbers. An estimate of 10 grams per meter squared per year gives a result of 3.3 GT of sequestered carbon per year across the whole ocean. This 10g rate of deposition is at the lowest end of the scale for what I’ve found. Since our industry oututs about 7gt of CO2 per year that amounts to about half of the total human output.
Climate science has struggled with defining the feedback response of this natural carbon sequesterization to increased CO2 concentration. Claims of acidification slowing down sequestration are not uncommon. We do have an extreme event though in history where CO2 was estimated to be 12% and limestone deposition rose to a massive 1mm/day or .36 m/year ending the global ice age called snowball earth. This was determined by simple geological evidence in sedimentary limestone from that timeperiod which makes it pretty hard to refute.
If we consider that today at 380ppm we have an estimate of .1 mm/year and at 120,000 ppm we have 360mm/year we can estimate the feedback to CO2 from ocean limestone creation.
380ppm / 0.1 mm/year = 3800 CO2 concentration vs sequesterization
120,000ppm /360 mm/yr = 333 CO2 concetration vs sequesterization.
So at much higher CO2 concetrations the oceans were on average 9 times more efficient at carbon capture than they are today.
A linear plot looks like this:
I’m not silly enough to believe a simple linear projection can solve this problem but IF we consider that these numbers have basis in measured rock formations, we are forced to realize this is evidence of strong natural feedback to CO2 concentration in the atmosphere. To put it further into perspective, if these historic numbers are to be believed, and we linearly interpolate between them, a doubling of CO2 from 380 to 760 would result in an increase in deposition rate to 1.06 mm/year or ten times today’s rate. I doubt very much that this is an accurate number but it shows the magnitude of the feedback from measured data vs CO2 concentrations.
Were strong feedback the case, why wouldn’t we have seen a stabilization of CO2 levels or a reduction in the buildup? Time for some handwaiving on my part.
- atmospheric CO2 and ocean Co2 buildup are separate issues. The ocean concentration is what affects ocean plants so there could be a long lag time before the feedbacks become fully active.
- The deposition may have already increased but the increase is masked by atmospheric output of global industry.
- Variance in ocean concentrations may drive some atmospheric concentrations. Ice cores blend CO2 over a fifty to a hundred years before the CO2 is encapsulated, perhaps some of what we are seeing in rise is due to release from oceans.
- Historic deposition numbers are overestimated for unknown reasons.
What we cannot discount though is that there was substantially greater deposition rates by biological processes at 15% CO2 concentration as compared to .038%. This huge deposition happened in what (according to today’s climate science) had to be higher acidity oceans, which means life somehow adapted to the CO2 and managed to create shells and limestone even in high carbon environments.
Of course, I don’t know much more than this but find the whole concept of natural CO2 capture both interesting and poorly understood in climate science. This could very well explain why the ‘sinks’ are not saturating as has been predicted by many in climatology.