Perhaps it’s all about the trees and pond scum…
There have been several anecdotal reports of trees with larger leaves this year or of increased crop yields (up to 20%) being attributed to the larger CO2 fraction of the air giving us CO2 fertilization of plants (this effect is known to exist – greenhouses will run the ppm of CO2 up to about 1000 to enhance growth).
http://www.soils1.cses.vt.edu/djp/4344hp/4344handout/unit2/photolimit.pdf has a few nice notes about CO2 fertilization.
http://www.soils1.cses.vt.edu/djp/4344hp/4344handout/unit2/photoplant.pdf has detailed description and a couple of graphs.
http://bomi.ou.edu/luo/pdf/sensitivity_and_acclimation.pdf has a more detailed look with partial pressures instead of ppm.
http://scholar.simmons.edu/bitstream/handle/10090/4026/145.pdf?sequence=1 is an interesting honors paper that looks at peat and the response to fertilization (not just CO2) but includes a CO2 response plot down at the very bottom. It gives an idea how complex it can be to try and figure out where all the carbon goes and why.
A couple of other interesting charts and a photo showed up on WUWT:
Are We Short of CO2?
This lead me to wonder if there might be a CO2 shortage in the air at 350 ppm which lead me to wonder just how fast an acre of forest might be able to pull the CO2 out of an acre of air. Forests are pretty good at putting up mass on an acre of dirt (though algae in pond scum can do it about 10 times faster…) so I thought I’d use a forest as my muse.
“Fast growth” species can yield up to 50 tons per acre (those are ‘wet tons’ – it’s about 25 tons of dry carbohydrate per acre as a mix of lignin, cellulose, etc. in the wood component. I’m ignoring the fraction in leaves because it’s wood that I have the statistic for. Just remember that the actual total biomass is significantly higher since we’re ignoring the leaves and roots… but conservative estimation is your friend.)
I must admit, my initial guess was “way off” in that I thought it would be something like 2 or 4 years for a forest to scrub the air above it. (Though I had the worry that it might be more like 10 or more…) The reality is a bit different.
I’ll be doing this in acres, feet, pounds, etc. because I happen to know key numbers in those units. Those of you who live in metric land, well, when we get to the end it’s just ratios and those don’t care what units you started with. At some point I may come back and turn this all into those weird seized metric units. (Tea takes two teaspoon of sugar, not 10 ml after all… since I don’t have an ml spoon nor the patience to put 10 of them in my tea 8-)
An acre is a little less than 209 feet by 209 feet ( 66 x 660 was the traditional measure – which makes more sense as one “chain” by 10 “chains” or 1 chain x 1 furlong or what an ox could reasonably plough in a day) , more or less. A common shorthand is to say that an acre has about 44,000 square feet minus 1% (43560 square feet). An acre is about .4 or 40% of a hectare. Since I’m only interested in a single unit of precision (years) having a bit of fuzziness in the 2nd, 3rd, or 4th digits doesn’t matter.
Now at 25 tons (figure 2000 lb tons, not the 2200 Tonnes that match the metric ton, again, just to put in a 10% conservative fudge – if you are estimating, you want all the errors to go against your thesis. Then if shown true, the thesis will only get more support as you ‘tighten up the numbers’…) that will work out to be 50,000 lbs per acre per year of carbohydrate.
So what’s that carbohydrate as CO2?
Carbohydrate is a repeating unit of a carbon and a “hydrate” or H2O so it’s molecular structure is made of H2CO repeating units. We’re going to skip a bunch of fine detail about end of carbohydrate chains and the presence of some nitrogen and a few other things. (We do, after all, have some “fudge” the other way built in all ready with 2000 lb tons and such). At the first digit of precision, you can estimate a tree (dry tree) as being made of H2CO monomers. But air has CO2. So how to convert?
Take your CO2 and figure it’s weight: C is 12 and O is 16, so it’s molecular weight is 44. (12 + 2 x 16) H2CO is made of hydrogen at 1 and the same C and O but only one O (the other one went into the air for us to breath). So the monomer molecular weight is 2+12+16 = 30. So for every 30 of dry tree we pulled 44 of CO2 out of the air. Our “carbohydrate” conversion factor is about 1.46 which means that for each ton of dry tree we pulled about 1.46 tons of CO2 out of the air.
That 50,000 lbs / acre-year of dry tree is 73,3333 lbs / acre year of CO2.
Divide that by 43,560 and you get 1.68 lbs of CO2 pulled out of the air per year for each square foot of forest.
What’s in the air?
So how much CO2 is on a square foot?
Well, we have about 14.7 lbs / sq. inch of air pressure, so that’s, about 2117 lbs / square foot. But only 350 or so parts per million of that is CO2, so we need to multiply that 2117 by 350/ 1000000 to get about 0.74 lbs / sq.ft of of CO2 in air. (Assuming ppm by mass, if ppm volume it will be different by the ratio of 44/28 or 1.5 times that much, roughly)
So a Forest scrubs how much air?
OK, so we’ve got 1.68 being pulled out, but only 0.74 available. I make that a ratio of 2.27. Lets just call it “2” so we don’t have a lot of False Precision, OK?
So a “fast forest” species like Poplar or Eucalyptus can completely deplete about twice as much volume of air as sits above that forest (all the way to space) and a fertile pond growing pond scum could completely deplete about 20 times the volume of air as sits above it. In one year.
So let me think about this for just a minute… If I grow a fast forest for 50 years, it will completely deplete 100 times the volume of air that sits above it. So 1% of the planet surface being these fast species would completely scrub all present CO2 from the air in one lifetime… 75 years in the PPM by volume case.
And pond scum could do it in 5 years. 7 and a bit years if CO2 is ppm volume. (Which I think it is, per wiki).
I think I know now why plants are CO2 limited in their growth. They have scrubbed the CO2 down to the point where they are seriously unable to grow well. Otherwise they would have removed it all not very long ago in geologic (or historical) time scales.
I come to 4 conclusions from this:
1) We desperately need more CO2 in the air for optimal plant growth. Plants must have depleted the air to the point of being seriously nutrient limited.
2) Any time we want to scrub the air or CO2, we can do it in a very short period of time using nothing more exotic than trees and pond scum on a modest fraction of the earth surface.
3) Biomass derived fuels will be CO2 from air limited in their production, especially if we start some kind of stupid CO2 “sequestration” projects. Siting biofuel growth facilities near CO2 sources (like coal plants) ought to be very valuable.
4) Any CO2 sequestration project that does get started by The Ministry of Stupidity needs to allow for CO2 recovery in the future. Things like ocean iron enrichment that sink it to the “land of unobtainable ocean depths” are a very bad idea. We are one generation away from CO2 starvation for our crops at any given time.
Not quite where I’d expected to end up, but enlightening all the same. Not only is CO2 increase not a problem, it is a valuable feature. And not only could we use plants to reduce CO2 in the air (if we wanted to), but we are in danger of them overdoing it all by themselves. Our biosphere is limited by the CO2 in the air and probably has been for some time.
One could speculate that the historical CO2 levels would indicate when CO2 was rate limiting for life and tell us when it was not; and thus indicate when plants were less stressed and growing much faster. It would be interesting to see if these times were followed by CO2 crashes to lower “modern” levels. I would further speculate that we all owe our lives to vulcanism dumping lots of CO2 into the air globally, because without it, the plants would have had a CO2 crash some time ago…which implies that when the planet U and Th runs down and vulcanism slows, we’re in a world of hurt…
Some words on Volcanos
It would also seem that in the midst of all the “settled science” the AGW True Believers like to talk about, we’ve just learned that we might not actually know how big various eruptions have been in the past. In discussing Chaitén (the volcano that gave the lightening rich eruption in the picture up top), some new research shows old estimates of eruption size can be very wrong; so we don’t really have a good estimate of past volcanic impacts…
Chaitén is still being active, and the pictures are nice too; but there are a bunch of other volcanos active right now. More than I’d expected… With a fair number of them in Ecuador.