Turned up to eleven: Fair and Balanced

Wednesday, June 18, 2003

Global Climate Change
David Appell's Quark Soup is a blog you should read every day, if you are interested in scientific topics of significance to the rest of the world. His style of description is lucid and entertaining, and he knows his stuff, about nearly everything, as far as I can tell. Anyway, an entry on Global Climate Change and Plants caught my eye, and I got into a very interesting discussion of the issues in his comments (full of unusually smart, pleasant, and eloquent commenters btw). The topic of the first article was the increase in net plant productivity (ie biomass) due to the rise in the earth's temperature, while the second article was that species diversity was being lost at the same time. In the comments, we discussed the questions of peer review (PNAS, in which the second artile is published, has an interesting peer-review process that allows National Academy of Science members to publish one paper per year with a much less stringent review), and the ways in which plants might react to changes in temperature or ppCO2 (partial pressure of CO2, essentially concentration). One of the things to note here, I think, is that not only is the climate a very complex system including a number of less than predictable variables, but plants and animals and ecosystems are complex systems, and in the later case, complex systems containing complex systems. This necessarily implies uncertainty in modeling and interpretation. As a general rule, you build models with simplifying assumptions (after all, if the model is as complex as the subject, it is a replica, not a model!). Just to start at the most basic level, consider a plant. Now, a plant's life is considerably simpler than ours, in many ways- it doesn't have to move, it makes its own food using sunlight and CO2 from the atmosphere, it replicates by sending out seeds by various mechanisms (wind born, insect vectors).
But if we look closer, some complexities arise (puts on microbiologist hat). Plants are colonized by a number of species of bacteria, some with beneficial effects, some harmful. For example, while I said plants make their own food, that is technically a lie (hey, maybe I could be a White House Press Secretary someday!). Bacteria need other things besides carbon and energy to live. We usually (that is, us microbiologists) think of organisms using carbon, nitrogen, and energy to live. "But wait", you might say, thinking you have caught me again, "the atmosphere is 80% nitrogen; so the plant can just use that, right?". No, you silly little person, it can't, so there! The "fixation" of nitrogen from the atmosphere is the conversion from N2 gas to ammonium, which is then used to synthesize amino acids, which are the building blocks of proteins, which all living things need to live. This fixation of nitrogen is only carried out by bacteria. The best studied of these is Rhizobium, a plant root symbiont which forms a nodule in which the bacteria convert N2 to ammonia. The symbiosis is complex, but vital to the survival of both species.
What does this have to do with the "greenhouse effect"? Well, possibly nothing, but I suspect that we have a lot more to think about when we posit ideas like "more CO2 in the atmosphere will make more plants grow, which will take the CO2 out of the air, leading to homeostasis." When I was in college, and I took a course in Environmental Bio, I thought something along these lines. And, incidentally, I am certainly not convinced that this is totally off base. However, if there is one thing geology and paleontology teach us, it is that over the long term, the earth is not homeostatic. The changes are massive, and they clearly result in extinction on a massive scale. So the suggestion that we can blithely go on without trying to figure this out, because the planet will right itself, is bullflop, grade A bullflop. The planet may well right itself, but we may not be around to see it (or, lots of other things that we really like may not be around to see it). So here's the question-suppose plants are capable of increasing their uptake of CO2? Will it be all plants (not bloody likely)? Will it be plants we like (who knows?)? How will it affect other parts of the ecosystem, and what will be the rate limiting step?
All of this says nothing, of course, about how plants and animals will fare under a changed climate. Again, however, I think this misses the point. If the climate changes as predicted (a big if, naturally), the equatorial regions will get hotter and deserts will expand. Storm activity will intensify, endangering people who live on coasts (and conceivably making inland areas coasts-hey that could be a good deal for me!). Optimal farm climates will shift northward, and the regions for various types of cultivation will shift (this could affect sharply niche commodities, say that only grow on very high altitude, very wet regions, or some such). All of this will not matter one bit to the planet-it will keep circling the sun just as it has for eons. It will matter to many creatures that live here, however, not least us.
On a related note, most of the big fish are gone. Like I said, its not the planet we should be worried about, it's us.