Greening the Earth with CO2: A good thing?

Despite what skeptical websites like this would have you believe, our uncontrolled experiment in CO2 enhancement (35% and rising!) is unlikely to end favorably on our already overstressed planet. Even without considering a radiative forcing of ~1.5 W m^-2 and its heating,the enhancement of CO2 is likely to have many negative impacts on our environment.

Plants are likely to be subject to so-called CO2 fertilization, wherein the additional gas added by humans allows plants to grow more quickly. It's a physiological fact that vegetation needs CO2 to enact photosynthesis. But different plants react differently. Some show a strong response while others react more slowly. Recent observations and research are beginning to discern some of the details of how this fertilization works.

• Poison ivy seems to be particularly responsive to enhanced CO2. It and other vines are have shown an increase (by a factor of 10!) in South Carolina. In general, weeds seem to respond especially robustly to this effect.

• Mixed aspen-and-birch stands bathed in extra carbon dioxide grow about 45 percent faster than their untreated neighbors. To sustain that speedy growth, the experimental trees had to find a way to extract more of the essential nutrient nitrogen from the soil.

The birch trees seem better at nitrogen foraging than aspens... In mixed stands of aspen and birch subjected to elevated carbon dioxide levels, birch trees increased recent nitrogen acquisition by 68 percent, compared to a 19 percent increase among the aspens.

• As atmospheric carbon dioxide levels continue to climb shrubs and other woody plants will likely dominate grasslands, altering pastoral lifestyles around the world...

...some of the ecosystems that are potentially most responsive to CO2 are grasslands and savannahs in the South[ern Hemisphere]... these are also some of the biggest ecosystems globally.

The effects of elevated CO2 may already be in play, as indicated by fairly consistent evidence of "bush encroachment" or "shrub encroachment" in many grasslands of the world...

While these changes may seem quite benign on the surface, they actually pose many subtle threats. By altering the composition of forest and savanna ecosystems, we affect the biodiversity in that particular biome. The effects of this alteration are unknown but are unlikely to be positive. Such changes can contribute, among other things, to species extinction, enhance summer flooding by altering water uptake and/or change the fire regime. These effects can act as further feedbacks on the environment, further accelerating change.

The fact is that we humans remain quite ignorant about the workings of the ecosystems of the Earth. It is quite arrogant of us to think that we can alter our environment willy-nilly and not expect problems to arise. We certainly don't know enough to manage the problems; any 'solutions' we try are just as likely to worsen the problem as they are to fix it. Even discounting the warming effect of CO2, the evidence suggests that our “enhancement experiment” is not going to end well. The best thing we can do is to act to slow down or even stop the experiment by reducing our emissions of greenhouse gases. It is the responsible thing to do for future generations.