In fairness, I need to admit that some researchers do try to come a little closer to Real World experimentation when speculating on the effects of rising CO2.
A reader on Free Republic brought to my attention a study conducted by the Marine Biological Laboratory of Woods Hole, Massachusetts that actually went through the trouble of conducting its simulation outside (in a North Carolina forest owned by Duke University). As summarized by Nature.com, May 30, 2006:
In the study, Mohan and her co-workers pumped extra CO2 over three large circular plots of North Carolina pine forest. For six years, the plants inside were exposed to an extra 200 parts per million of CO2 over today's atmospheric concentration of about 380 parts per million, roughly what we might expect from pollution by the middle of this century.I think this team did a much better job of trying to approximate natural conditions than did the team in the other study. But... two thoughts come to my mind pretty quickly:
Other research has suggested that vines tend to grow particularly fast in response to higher CO2 levels, and that vines are increasing in abundance all over the planet. Unlike trees, which use extra carbon to grow more wood, vines use it to produce more leaves. The extra leaves help the plant to harvest even more CO2, the cycle continues and the vines flourish.
Mohan's experiment sought to check whether the plants shoot up in the wild, as they do in greenhouse experiments. "Yes, dramatically," was the answer. The poisonous ivies grew at double the rate of plants grown under regular CO2 levels, whereas woody species on average tend to grow around 31% faster. The elevated CO2 also created a nastier version of urushiol poison, the team showed.
[...] By extracting urushiol from the plant's leaves, the researchers found that poison ivy grown in high CO2 churned out more than 150% more of one nasty, unsaturated form of urushiol and around 60% less of the mild, saturated form.
The researchers aren't sure why this chemical shift took place, but one idea is that the increased availability of carbon somehow favours the chemical reactions that produce the unsaturated forms of urushiol.
- The study was premised on the IPCC guesstimate that atmospheric CO2 would rise from the current 380-ish ppm to 570-ish ppm by mid-century. As much of IPCC's work has given me reason for skepticism, I decline to swallow this prediction uncritically.
- The planet's ecosystem is so complex, I don't think a study performed in this manner can authoritatively tell us what would happen in the Real World if atmospheric CO2 did rise to this level.