Chaos theory holds that the flutter of a butterfly’s wings can have far-reaching effects. So, too, can increasing plant defense mechanisms, upsetting the natural order of things and threatening innocent species with extinction.
Could increased carbon dioxide (CO2)—a boon for plant health—be harmful to the organisms that feed off those same plants?
Not likely. Take butterflies, for example. Their future looks sweet indeed. Goverde and colleagues collected different types of a wildflower in and around Paris and grew the low-spreading plants at the natural level of 350 parts per million (ppm) and at 700 ppm. This particular plant produces cyanide compounds that fight against insects’ making a meal out of it.
One insect that does feed on this wildflower, however, is the common blue butterfly, which has an enzyme that detoxifies the plants. So these butterflies were introduced into the study to determine how elevated CO2 will ultimately impact this cherished member of the biosphere.
The scientists found that elevated CO2 increased plant biomass but decreased the concentration of leaf cyanoglycoside without impacting leaf water, sugar, protein, or nitrogen contents. The butterflies enjoyed the better-tasting wildflowers, and those in the elevated CO2 chambers increased their consumption of leaves, their mass increased, and the larval developmental period decreased. Furthermore, mortality decreased for those butterflies feasting on the CO2-enriched plants.
Indirectly, the common blue butterfly is benefitting already from the CO2 emissions of the Industrial Revolution; this butterfly (and probably many others) would certainly be blue if CO2 emissions were stabilized.
Funny how those supposedly disappearing butterflies in Mexico made global warming headlines worldwide a few years ago, yet the Goverde study received essentially zero publicity. When it comes to butterflies and global warming, only bad news seems newsworthy.
The effects of global warming on insects are also failing to make headlines. If plants put down their defenses, won’t other herbivores come along and gobble up all the increased plant biomass? Well, a second recent paper shows us that not all insects will emerge as lucky as the common blue butterfly; consider the future of the bird cherry-oat aphid.
Newman and colleagues grew tall fescue plants for two weeks in open-top chambers with atmospheric CO2 levels maintained at 350 ppm and 700 ppm. At that time in the experiment, the tall fescue was inoculated with 20 aphids per plant and grown for an additional nine weeks with the differential CO2 levels.
The team found that the doubling of CO2 increased plant dry matter production by 37 percent, but the total number of aphids decreased substantially. Unlike the butterflies, the aphids seemed to lose out.
Hmmm. . . . Be good to butterflies and emit CO2—or be good to aphids and adopt the Kyoto Protocol?
From these two studies, we learn that increased atmospheric CO2 concentrations will cause a) wildflowers and fescue to grow bigger and healthier, b) beneficial butterflies to grow bigger, more quickly, with lower mortality rates, and c) the number of rose-ruining aphids to decrease. These hard facts come from reproducible studies that have survived the peer-review process.
It’s as simple as the birds and the bees—increased CO2 will strengthen the biosphere and make the Earth a better place.
When I see a picture of the Earth from space, I do not see a fragile world with its climate system hanging on a thread. I see a global ecosystem crying out for higher levels of CO2.
Robert C. Balling Jr., Ph.D. is director of the Laboratory of Climatology at Arizona State University and coauthor of The Satanic Gases.
References
Goverde, M., et al., 1999. Influence of leaf chemistry of Lotus corniculatus (Fabaceae) on larval development of Polyommatus icarus (Lepidoptera, Lycaenidae): Effects of elevated CO2 and plant genotype. Functional Ecology, 13, 801-810.
Newman, J.A., et al., 1999. Elevated carbon dioxide results in smaller populations of the bird cherry-oat aphid Rhopalosiphum padi. Ecological Entomology, 24, 486-489.
