CO2

Currently, we just step outside and measure it. Do so in a place where local sources and sinks dominate, a wide range of values can be found. But all that has been seen to.

Paleo CO2 is more challenging. Half a million (maybe a million) years of ice-core bubbles, but before that is from proxies. Warts and all, I am tempted to attach a graph.

Between 350 and 300 million years ago CO2 crashed. It went into coal, and the mechanisms are pretty clear. Photosynthesis soundly beat decomposition. You might be amazed how little coal has formed since those good ol' days.

Most interesting thing since then was PETM, 55 Mya. CO2 had a big bump, probably from marine exhalation. It was warm then also.

Since then it has been downhill for CO2, apparently related to new groups of plants that got ever better at extracting it from the air

Damn plants don't seem to care if they cause ice ages! Thoughtless. And yet they are edible (where nothing else is) so we have to put up with them.

Only most recently have we extensively burned fossil C amd turned the tide. Now CO2 is back on the up at 400 ppm, and we can probably get to 600 by the end of the century. With how much associated warming? Well, that's the question eh?

But don't let it slip your notice that most of the CO2 is in the oceans. Depending on how you count, it can be 95% against the atmosphere's 5%. Those sound like how warming is distributed between these fluids, and so they should.

Cautious to avoid fear mongering, I can only say that it would be very wise to try to avoid anything like the PETM.

Very very wise.

Meanwhile plants are growing better. Crops might not be putting on as much protein, but people are working on that. Herbivores (some competing with humans for food) are getting more frisky, but people are working on that also. We will probably patch to together the agricultural enterprise for the rest of this century.

But if CO2 later increases even more, well...

People not yet alive might be very very wise to keep that from happening.

Anyway, what is your favorite CO2 concentration, and why?

 

Comparing CO2 and air T can be done directly over a (few) century scale, or for much longer, using proxies for one or both of the variables. It makes a big difference in the slope of the correlation. On a century scale the slope is small. I think all here would agree. This is our source of hope that near-certain future +CO2 won't make things unpleasantly warm. I suppose it has a lot to do with the thermal inertia of the vast ocean blue.

On longer time scales the slopes are greater. Those could be doubted, since proxies are indirect. They are being improved though. It seems clear that to reach (Mann-ish) levels like 6 oC per CO2 doubling, other factors (like Earth albedo with very different ice coverage extents) need to be invoked.

In other words, CO2 is not everything, people get that, and the effects of CO2 depend on the time interval being considered. The notion of 'only CO2' is, I am afraid, an imaginary construct unappealing to people who study the subject.

This won't prevent me from discussing CO2 though, because it is fascinating. Next up for y'all will be a couple of chemistry lessons. Get your dread ready

 

Yet another purpose for the graph mentioned here again @3 is to illustrate how much T does vary over 1000-ish time scales when CO2 is not varying much.

T does jump around, say the proxies, by 1 oC or so. On longer time scales, it varies more, but then you get back to CO2 concurrent changes.

 

...

 

Bob disagrees about the short-term correlation slope, but IPCC summarized research is 2.x degrees +/- large. That 'large' is one reason why coal remains king.

 

So, I pretend that somebody here is interested in measuring CO2. This has been in the realm of ‘bench chemistry’ pretty much since people knew what acid and bases were. Chemicals are not expensive, and widely available because they are insufficient to make dr*gs or b*mbs.


A bit of care is required, mostly so you don’t get NaOH or KOH in your eye (risk of loss of visual input function). With a bit of practice you can obtain 10 ppm accuracy. If you go hardcore, 5 ppm. Students laugh when they see me do titrations while breathing through a long tube. That’s because they don’t appreciate that we exhale CO2 at 10 percent. A little of that goes a long way.


So this is achievable, and has been for a couple of centuries. Some famous older studies showed urban concentrations (Paris, etc.) to be above 500 ppm. This is (and was) not incorrect. Unfortunately those studies are famous because they did not know what we do now, that cities are places where burning and respiration outweigh photosynthesis.


Brings us to Charles Keeling, famous for CO2. He started his grad school research to find out what CO2 concentrations are and how they varied. He went all over California and was stymied by aspects of ‘local biology’. He ended up on top of a Hawaiian mountain, where the ‘free’, well-mixed troposphere could be analyzed. He did the chemistry a much more difficult way, by manometry. Can get 1 ppm accuracy like that, but it’s really hard to do.


The initial finding of an annual CO2 cycle was a big deal. Naturally some folks thought he was wrong. But no, here was an excellent chemist measuring (for the first time) something that the Earth simply does. After a few years, the longer upward trend because apparent and now, that is almost the only thing we talk about.


Next technology after manometry is infrared spectroscopy. Keeling resisted that for years, and only after extensive inter comparisons made the switch. The first IR spectrometers were huge and expensive, but now they are neither.


You have your choice of the $200 unit from a company in Florida that specs 20 ppm but can be set up better for 10 ppm. That is about what you’d spend on your chem. lab, and with no risk of putting your eye out. It is fast. Plugs into a USB port. Anybody who is generally capable of tying their shoelaces can operate it.


Your next choice is $3000 from a company in Nebraska that specs 1 ppm. This and from a competitor in UK are the most common science choices, because ‘white coats’ often have that kind of money to spend. Has a bit of a learning curve, but I have taught 9 yr olds.


The infrared technology is based on selecting two, appropriate IR wavelengths. One where CO2 absorbs and the other not. Measure light extinction (it does not disappear, it gets converted to a little bit of heat), let the box do math, and there’s your data. Both the above do something like that, but details of design are key in getting 1 ppm resolution.


Interestingly, if you choose three IR wavelengths, you can measure water vapor as well. The one does not interfere with the other (wavelengths well chosen). You can measure CO2 up to at least 5% with no water interference. Of course this contradicts notions ‘CO2 is saturated’ and ‘water vapor already absorbs all the IR’. But such notions do not arise from chemistry and physics.


Spend even more and you can do even better. Free path CO2 analyzer looks like a big claw. Something like $10,000. It tells you how much there is in 10 cm of air just passing by; you don’t have to move a chunk of air into a magic box. Rich carbon-cycle researchers will buy several of these (presumably instead of Ferraris) and hang them off towers. This reveals CO2 dynamics of your forest or cornfield in exquisite detail. Some people want to know such things…


One more and we’re done. Laser cavity ringdown spectrometers also work in the IR, but they slice up wavelengths extremely finely. With this, you get not just real time CO2, but also the stable isotope ratios of 13C and 18O. Now you can figure out exactly where those molecules of CO2 came from. Gotta tell ya, this is the thing for carbon cycle research. Unimaginably beyond 19th century titrations. About $120,000 for the box, so one really has to want to know.


The last two were hitting the scene just about when Charles Keeling died. Too bad. He was one of the greatest 20th century chemists stubbornly clinging to 19th century techniques. He deserved to have nice toys.


I’d much rather have an LCRDS than a Ferrari, but unfortunately my friends in Santa Clara CA won’t ‘loan’ me one. Love ya anyway Picarro!

 

Don’t have Picarro but still want to know isotope ratios? Fine, revert to 19th century chemistry. Trap the CO2 in alkali and precipitate it with strontium chloride. Sr sounds bad because the 90 isotope is such a bad boy in atmospheric nuclear testing. However, Sr by the bottle is much less toxic than Barium also used for this. No idea why chemists allow ‘kids’ (grad students) to work with Barium; kids are apt to put fingers in eyes and mouths.


Anyway, the amazingly fun part of this is adding the SrCl2 to the trapping solutions. The ‘snow globe’ effect immediately occurs. I was unprepared for the beauty. Much dancing and clapping.


Then it gets mundane, centrifuge and mass spectrometer, which are common ‘appliances’. Carbon cycle gets traced on the cheap, with a beautiful step you must not miss in the middle.

 

If CO2 had no climate effects, it would still be worthy of study. This planet is populated solely by carbon-based biologicals. It is necessary for photosynthesis and (nearly) unavoidable for respiration. The photosynthesis guys already got their Nobel prizes for darn good work. The decomposition guys (like me) are way behind the curve.

This behindness, and how it might get fixed, is THE THING. I am inclined to ask this to be a 'climate-free' thread just so we can talk about the carbon cycle. It is more fun than you can imagine.

 

If CO2 goes way up to 600 ppm and then no more added, how fast might it come down?

Next time, me hearties.

 

Nah you don't. You only know how fast new volcanic minerals and those exposed by erosion has removed CO2, based on paleo. Comes down to it, nobody knows how fast geology and biology could do this, if we turned our attention to the processes.

We need numbers. New net addition of CO2 to the atmosphere is 5 Pg C y-1, with half of the gross (10) already consumed biologically. Which we don't understand, because DECOMPOSITION, as I said above.

Moving the atmospheric load from 600 to 400 ppm means 400 Pg C needs to be 'sunk'. Well, OK, where and how fast?

Handling wood differently, and afforestation, and soil carbon in ag systems, and charcoal in soils could each sink about 1 Pg C y-1. Costs for these vary. Marine iron fertilization has yet to be accounted in this way, but it has an added advantage of countering marine pH reductions. Direct geological down-injection of CO2 has yet to be accounted in this way. Grinding up pyroxene mineral (which loves CO2) has yet to be accounted in this way.

I simply want to say that were it an accepted goal to remove 400 Pg C from the atmosphere, it could be achieved at a century scale. But then, there is the cost.

Governments and companies have their own preferred ways to use funds. The main goal, thus far, has been to make rich people richer, and I have no standing to dispute that. If the West Antarctic Ice sheet dumps a half meter of sea level, then more powerful voices than mine will be heard.

The main thing for optimists (like me) is to not miss the accounting. We (collectively) have pumped up CO2 by such an amount over a century and a half. We could by choice, reduce it as much in the same time or possibly a bit less.

Part of the engineering problem remains. But mostly it is a money and political-will problem. And there it will remain, unless and until somebody important says "we should all care about this'.

The crap would be if we did all such above and still got an undesired climate. Friendly_jacek has hinted at slow T/CO2 responses (perhaps without meaning to do so), and there are many climate studies that have suggested the same. This is what fear-mongering alarmists mean when they say ' it is already too late'.

But hey, we don't know that, and maybe 20 years hence we'll feel obliged to put on the brakes. Maybe, it will work.

I SO DID NOT WANT this to be a climate thread. I want to talk about biological CO2. My version of re arranging Titanic deck chairs.

 

Just above
"Most of the CO{2} is sucked up by photosynthesis every year only to return by plant decomposition." If this is the only thing you got from coursework, it would be enough How could we possibly get this into the mind of John Q. Reader. It informs EVERYTHING.

Land ecosystems do X. Marine ecosystems do Y. X and Y are about the same.

If one wants biological processes to reduce atmospheric CO2, the decomposition needs to be made smaller than photosynthesis. #1 it already is, by about 5 Pg C y-1. #2 Widen that gap wherever you care to spend the money.

I love the idea of making dead wood decompose more slowly, but unsuccessful in the attempt. When dead wood lingers in forests, it hosts much biodiversity, Three books written on that. Bury or sink it instead? Read Ning Zeng in Carbon Balance and Management. Or Scholz.

Our agricultural enterprise would be better served by sinking carbon there. Researchers are all over this but I must say that no big money is in support. Yet, farmers don't want Ferraris, they want a big crop to sell next year. They are still paying for the land and harvest equipment.

Biological C sequestration won't work, on net, if forests have above-average burns. I don't like this year in that regard. ENSO is still deciding how big to be. You know what's weird? Nobody has counted CO2 from fire fighting against (plane fuel etc.) against CO2 not released because of the fight. NOBODY. You want to get a paper into a top journal, well there you go.

We can just sit here and talk about this or that aspect of the carbon cycle. But a day may come when people actually want to make CO2 go down. It would be good to put some numbers on whatever scheme, hairbrained or otherwise.

 

Austin_G I think we are shooting for 600 ppm. If,along the way, it gets too warm or seas too high, some sort of serious actions will follow.

The carbon pool of most interest to me is in soils. How this will 'behave' in the future is included in most global climate models, but not in a way I find satisfying. Too many things dramatically change soil organic carbon (SOC) on local time and space scales, that are not yet in models. And we only know how to do experiments on those global scales. In the interest of increasing local boredom, I want to show one figure from one model comparison:

Earth Syst. Dynam., 6, 435–445, 2015
http://www.earth-syst-dynam.net/6/435/2015/
doi:10.5194/esd-6-435-2015
Decomposing uncertainties in the future terrestrial carbon budget associated with emission scenarios, climate projections, and ecosystem simulations using the ISI-MIP results
K. Nishina, et al.

I talk about it first. The third set of panels refer to SOC. Please note that the aggregate uncertainty of future SOC is higher than anything else on the page. And this is with many SOC-changing processes not yet in the models! These 100 to 200 petagram C uncertainties could be compared to net annual fossil C increase in the atmosphere, which is 5. This is why people like me don't find soils boring.