To sequester all of the annual atmospheric increase in CO2 with a citrus forest having a 30 tons per hectare per year CO2 uptake, an area equivalent with 0.8 that of Australia would need to be in active cultivation. A juvenile forest would sequester for some 20 years until the forest reached maturity. Henceforth, trees would need to be replanted and if the dead wood were left to decompose and return carbon to the atmosphere, the sequestration value would be for ‘just’ 20 years. …Hypothetically it does not sound like such a bad deal, 20 years. Yet again, the Australian outback is indeed enormous, equivalent with 50 times the area of New Mexico or 20 times Oman. Clearly massive scale reforestation should be widespread globally. Ambitious? God yes! Worth it? Hell yes!
The effects of elevated CO2 on plants can vary depending on other environmental factors. While elevated CO2 makes carbon more available, plants also require other resources including minerals obtained from the soil. Elevated CO2 does not directly make these mineral elements more available and, as noted above, may even decrease the uptake of some elements. The ability of plants to respond to elevated CO2 with increased photosynthesis and growth may therefore be limited under conditions of low mineral availability. This effect has been best documented for nitrogen. In FACE experiments, there is less enhancement of photosynthesis by elevated CO2 under low than high soil N conditions (Ainsworth & Long 2005; Ainsworth & Rogers 2007). Crop yield in FACE also appears to be enhanced by elevated CO2 to a lesser extent under low-N than under high-N (Ainsworth & Long 2005; Ainsworth 2008; Long et al. 2006). Across studies using all types of CO2 fumigation technologies, there is a lower enhancement of biomass production by elevated CO2 under low-nutrient conditions (Poorter & Navas 2003). Crops grown with low amounts of N fertilization also show a greater decrease in protein concentrations under elevated CO2 than crops grown with higher N fertilization (Taub et al. 2008).
Another environmental factor that interacts with elevated CO2 is atmospheric ozone (O3), a gaseous toxin. Ground-level O3 concentrations have been increasing worldwide (and are expected to continue to increase) due to increased emissions of pollutants that react to produce O3 (Vingarzan 2004). High atmospheric concentrations of ozone can cause damage to leaves and decreased plant growth and photosynthesis (Feng et al. 2008; Morgan et al. 2003). The primary location of O3 injury to plants is the internal tissues of leaves. Decreased openness of stomata under elevated CO2 can therefore decrease exposure of sensitive tissues to ozone. Elevated CO2 substantially decreases the negative effects of high ozone on photosynthesis, growth, and seed yield in both soybeans and rice (Feng et al. 2008; Morgan et al. 2003). Across experiments with all plant species, the enhancement of growth by elevated CO2 is much greater under conditions of ozone stress than otherwise (Poorter & Navas 2003).
Current evidence suggests that that the concentrations of atmospheric CO2 predicted for the year 2100 will have major implications for plant physiology and growth. Under elevated CO2 most plant species show higher rates of photosynthesis, increased growth, decreased water use and lowered tissue concentrations of nitrogen and protein. Rising CO2 over the next century is likely to affect both agricultural production and food quality. The effects of elevated CO2 are not uniform; some species, particularly those that utilize the C4 variant of photosynthesis, show less of a response to elevated CO2 than do other types of plants. Rising CO2 is therefore likely to have complex effects on the growth and composition of natural plant communities.
Most of the proposed solutions to climate change such as substitution of fossil fuels require large investments, policies that are politically contentious or difficult to enforce, and years to fully implement. However, some of the most effective and lowest cost opportunities for greenhouse gas (GHG) reductions are lifestyle choices that can be made today that cost little, and that are actually good for us. Chief among them is the decision to adopt a healthier, less meat intensive diet.
The significance of this opportunity was emphasized in a recent presentation at the World Bank by Jonathan Foley, director of the University of Minnesota Institute on the Environment. According to analysis by the Institute, every pound of meat is equivalent to about 30 pounds of grain production in its contribution to climate change when allowance is made for the full life cycle of livestock production. This is primarily because methane emissions from ruminants have a GHG impact roughly 25 times that of carbon dioxide.
Another expression of the resource intensity of meat production, Foley explained, is that even highly efficient agricultural systems like that in the US only deliver about the same calories per hectare in human consumption terms as poor African countries with more grain based diets. The surprisingly large role of livestock in global warming was explored in a 2009 article by Robert Goodland, formerly a World Bank economist, and Jeff Anhang, an IFC environmental specialist. They estimate that when land use and respiration are taken into account and methane effects are properly calculated, livestock could account for half of current warming when using a 20 year time-frame. According to Goodland and Anhang, replacing 25% of livestock products with alternatives would liberate as much as 40% of current world grain production with comparable benefits in reduced burdens on land, water, and other resources.