Global carbon cycle

We might set aside the question of CO2 effect on climate, and just think about the global sources and sinks of this gas, and how they compare. It certainly is of interest to me, and might be so for others at PC. For this purpose I link a recent publication

http://www.earth-syst-sci-data-discuss.net/5/1107/2012/essdd-5-1107-2012.pdf

Not because of its delightful writing style, because there are several papers on this and they all get bogged down in much the same ways So you are completely forgiven for skipping the text entirely and proceed directly to the figures. I think they are very nice and even, perhaps, user friendly.

Pretty much at a glance, you can see how fossil-C burn, land-use changes, and terrestrial and marine uptake compare in the recent decades. Older than that the accuracy of several of these terms drops off. A lot.

What I hope people can appreciate from these figures is how much terrestrial uptake varies from year to year. For example, the 'land' green-shaded in Figure 2. In strong El Nino years (like 1998) land uptake is zero. In contrast it was about 5 petagrams C in 1993. That range is huge! None of these other big fluxes have anything like that variation.

Sure, this is discussed in the literature and post-hoc reasoning abounds, such as warmer air and altered rainfall in El Nino years favors decomposition over photosynthesis. I find this unsatisfying, and a strong motivation to figure out why it happens. Field observations, manipulative experiments, and models based on biological mechanisms. Things like that. In no small way this is my reason to study terrestrial carbon cycling. It is hugely variable and a string of 5-petagram trapping years would be 'just the ticket' to keep atmospheric CO2 from increasing faster in the near future.

In that regard, in the same figure you can see that terrestrial uptake has had a string of nearly 10 pretty good years. Nice. And deserving of mention whenever Van Mantgem tells of global increase in tree mortality or Dai, the increase in drought. Both of those are accurate and I hold both researchers in high regard, but darn it, the land plants are really doing a good job.

Except, in some years, they don't and it is a sad admission that we really don't know why that is. I think it is important to understand it much better.

So, what do y'all think?

I said I would not talk about climate change, but I will in this one regard. In those models, the ocean heat storage jumps about from year to year, so the air T record looks all bumpy. But (I say) it is their problem to figure that out. In contrast, the ocean carbon sink (blue area in the same figure) just hums right along. As air concentrations have increased, the ocean (phytoplankton) just eat more. Compared to trees+decomposers, phytoplankton look very reliable. Maybe they won't appreciate lower pH water in the future, but they haven't said so yet.

 

The Gaussian approach bears similarity to how air T records from stations are converted to smoother geographical fields. Makes sense to practitioners, but smells like 'cookery' to people who can't or would not want to accept air T trends.

But as you say, the other covarying factors like sea-level rise, conspire to keep the practitioners honest.

 

Fair enough. I'd be very reluctant to pit my understanding against

Oceanic sinks for atmospheric CO2 - RAVEN - 2002 - Plant, Cell & Environment - Wiley Online Library

Which among other things, reminds us that there is a lot more bicarbonate in shallow ocean water than CO2 in the atmosphere. It would appear that the solubility (abiotic) pump is good to go, unless so much heating of shallow oceans causes thermal stratification that overcomes vertical mixing. Then, we'd be in a world of hurt.

BTW if you are interested in an expert on the biological carbon cycle who has published in a wide range of fields, John A Raven would be an excellent choice. I believe that the term 'polymath' applies.