Stanford Report, December 5, 2002
High carbon dioxide levels can retard plant growth, study reveals
The whole article is interesting, here are few tidbits:
“The logic is straightforward: Plants need atmospheric carbon dioxide to produce food, and by emitting more carbon dioxide into the air, our cars and factories create new sources of plant nutrition that will cause some crops and trees to grow bigger and faster.
But an unprecedented three-year experiment conducted at Stanford University is raising questions about that long-held assumption. Writing in the journal Science, researchers concluded that elevated atmospheric carbon dioxide actually reduces plant growth when combined with other likely consequences of climate change — namely, higher temperatures, increased precipitation or increased nitrogen deposits in the soil.” (emphasis added)
“In the past, people have argued that perhaps we don’t really need to worry about fossil fuel emissions, because increased plant growth will effectively pull elevated carbon dioxide concentrations out of the atmosphere and keep the world at the appropriate equilibrium,” he added. “But our experiment shows that we can’t count on the natural world, the unmanaged world, to save us by pulling down all the atmospheric carbon dioxide.” (Emphasis added.)
“Our study demonstrates that there is still a lot to learn about the factors that regulate global climate change. But we also know a lot already, more than enough to engage in a serious discussion about action to reduce carbon dioxide emissions from burning fossil fuels and clearing forests.”
We probably need to learn a whole lot more about a lot of things. The article talks about measuring growth in the presence of rainfall, nitrogen, warmth and CO2, finding CO2 to be a limiting factor. I don’t think the reporter has captured the concept however.
For their initial arguement, they use the following predictions from climate scientists “a doubling of atmospheric carbon dioxide; a temperature rise of 2 degrees Fahrenheit; a 50 percent increase in precipitation; and increased nitrogen deposition — largely a byproduct of fossil fuel burning.” If you think about it, that pretty much describes the inside of a greenhouse, warmer than the outside by a couple of degrees, CO2 levels forced to 1000 ppm (on purpose), nitrogen fertilizer and daily watering. Plants seem to do fine there or we wouldn’t use the greenhouses right? I know that’s simplistic, but close enough.
This where the reporting falls down, misleading the readers. Their results on yields of plant biomass are 84% over control plots for plots where nitrogen, water and heat are applied; and 40% in those plots where CO2 was enhanced. The authors of the study say “We got exactly the same results when we applied carbon dioxide alone, but when we factored in realistic treatments — warming, changes in nitrogen deposition, changes in precipitation — growth was actually suppressed.” Hmmm growth was actually suppressed. No, if the CO2 enhanced plots with heat, water and N2 got 84% increase, and similar plots with enhanced CO2 produced 40%, then there is still a 40% increase in growth. Their original paper didn’t make any claims of suppressed growth, only lower yield.
Here are their exact words “The three-factor combination of increased temperature, precipitation and nitrogen deposition produced the largest stimulation [an 84 percent increase], but adding carbon dioxide reduced this to 40 percent,” (emphasis added) The reporter seems to have taken this as retarding growth, a completely different thing.
“The mean net plant growth for all treatment combinations with elevated carbon dioxide was about 4.9 tons per acre — compared to roughly 5.5 tons per acre for all treatment combinations in which carbon dioxide levels were kept normal.” Either by oversight or by design, the reporter fails to say what the tons per acre were for the control plots. But wait, if the low CO2 plots got 5.5 tons/acre and the CO2 enhanced plots got 4.9 tons/acre, that’s about 89% of the maximum yield (4-9/5.5=0.8909= 89%) not 44% less, only 11% less yield. More sloppy reporting.
So, even in a worst case scenario, plant growth will still be higher by 40% in a CO2 enriched environment. How can that be considered to be retarded plant growth?
This looks like a case of poor reporting rather than junk science. The original report is in Science and is quite clear on the 84% vs 40% growth increase. Their methodology is quite inventive as discussed below.
Control, warming, elevated CO2, and warming plus elevated CO2 treatments were each applied to eight plots. Infrared heat lamps were suspended over the centers of the warming plots, heating the plant canopy by 0.8° to 1°C”, [not the 2°C quoted by the reporter.] “Atmospheric CO2 concentrations were elevated to ~680 ppm with a ring of free-air emitters surrounding each plot and delivering pure CO2 at the canopy level.
Bad reporting makes good studies look like junk science. Did the reporter have an agenda? I can’t say, but from reading the press rlease only, one gets a much different view than the authors had in mind. A lesson for all of us.
Just a little information on the atmospheric CO2, assuming that we are at about 380 ppm today and the observable increase is 0.5% per year, it will be 2122 when we can expect to see a CO2 concetration of 680 ppm. And by calculating the logarythmic effect of CO2 on temperature, that will give us maybe another 0.6 to 0.8 degrees C in warming. I think we might be ok for a while. And we might just find some alternate non-carbon energy by then.
