Could genetically altered trees and plants help to counteract global warming? Christer Jansson and a research team at Lawrence Berkeley National Laboratory and Oak Ridge National Laboratory just published a proposal for genetic engineering phytosequestration as the lead paper of a special section in the October 2010 issue of the journal BioScience.
Their quantitative analysis indicated that forests of genetically altered trees and other plants could sequester several billion tons of carbon from the atmosphere each year. That would help to ameliorate global warming, whatever one’s ideology on genetic engineering and one’s ideology on climate change.
[“Could Genetically Altered Trees, Plants Help Counter Global Warming?”]
The special issue of BioScience includes several points of view on the prospects for enhancing biological carbon sequestration. Other papers, beyond the scope of this story, analyze significant ecological and economic constraints that limit such efforts. One might, for instance, sequester carbon by culturing algae to produce biofuel feedstocks, modify the regulatory stance of the government for producing genetically engineered trees in the United States, or understand societal perceptions of the issues surrounding the use of genetically altered organisms to ameliorate warming attributed to the buildup of greenhouse gases.
The relationships between plants and the global climate are complicated and imperfectly understood. On one hand, trees and other plants help to keep the planet cool. On the other hand, rising levels of carbon dioxide in the atmosphere seem to be turning down the controls on the global air conditioner. One new study by researchers at the Carnegie Institution for Science states that in some regions of the world more than a quarter of the warming from increased carbon dioxide is due to its direct impact on vegetation.
[“Carbon Dioxide’s Effects on Plants Increase Global Warming, Study Finds”]
“Plants have a very complex and diverse influence on the climate system,” says Ken Caldeira of Carnegie’s Department of Global Ecology. “Plants take carbon dioxide out of the atmosphere, but they also have other effects, such as changing the amount of evaporation from the land surface. It’s impossible to make good climate predictions without taking all of these factors into account.”
We know less about the organisms in the oceans and their role in climate change, but we have long known that plants on land perform evapotranspiration, a process that gives off water through tiny pores in their leaves, cooling the plant just as perspiration cools our human bodies. On a hot day, when dogs pant to cool themselves, a tree can release tens of gallons of water into the air, thus acting as a natural air conditioner for its immediate surroundings. Plants absorb carbon dioxide for photosynthesis through the same stomata (a type of pores in leaves). However, when carbon dioxide levels are high, the stomata shrink. Then less water is released, dialing down the tree’s cooling power.
The general warming effects of carbon dioxide as a greenhouse gas have been known for quite a long time, says Caldeira. He and fellow Carnegie scientist Long Cao were concerned that it is not as widely recognized that carbon dioxide also warms our planet by direct effects on plants. Prior work by Carnegie’s Chris Field and Joe Berry indicated that these effects were important. “There is no longer any doubt that carbon dioxide decreases evaporative cooling by plants and that this decreased cooling adds to global warming,” says Cao. “This effect would cause significant warming even if carbon dioxide were not a greenhouse gas.”
If Global Warming is real, as nearly all scientists believe, this is not itself caused by plants. In the words of the Science Daily article, “Global Warming: The Blame is not with the Plants”: “Details of calculations used [by scientists in a Max Planck Society study] linked global methane emission estimates to plant growth, which is generally quantified as net primary productivity (NPP). On a global basis NPP amounts to ~62 x 1015 g of carbon/yr, which corresponds to an uptake of 227 x 1015 g of CO2/yr. On the emission side, our study suggests annual global methane emissions by plants of 62-236 x 1012 g/yr CH4. Thus, for each kg of CO2 assimilated by a plant roughly 0.25 to 1 to 4 g of CH4 is released. During growth of a new forest, up to 50% of plant tissue is lost again in the short term through decomposition of plant litter of leaves and roots. This then doubles the estimate to 0.5 to 2 g methane emitted per kg of CO2 assimilated and stored in plants for longer periods. Over a 100-year horizon, the global warming potential of methane is ~20 times higher than that of carbon dioxide. Thus, for climate, the benefits gained by reforestation programs would be lessened by between 1 and 4 per cent due to methane emissions from the plants themselves.”
A more recent analysis led by scientists headed by one with the appropriate name A. Anthony Bloom, at the University of Edinburgh, [“Study Gives Green Light to Plants’ Role in Global Warming”] suggests that plant leaves account for less than one per cent of the Earth’s emissions of methane — which is considered to have about 20-25 times more impact than carbon dioxide in causing global warming.
The study by Christer Jansson, Stan D. Wullschleger, Udaya C. Kalluri, and Gerald A. Tuskan outlines a range of strategies for, in various ways, augmenting the processes that plants use to sequester carbon dioxide from the air and convert it into long-lived forms of carbon, first in vegetation and ultimately in soil. They emphasize that the potential use of genetically engineered plants, for carbon sequestration, as opposed to controversial food crops, is only one of many policy initiatives and technical tools that might increase the level of carbon sequestration which already occurs in natural vegetation and crops.
They consider genetically altering plants, thereby:
(1) increasing the efficiency of plants’ absorption of direct or scattered sunlight;
(2) making them send more carbon into their roots where some may be converted into soil carbon and remain out of circulation for centuries;
(3) making them better able to withstand the stresses of growing on marginal land, improving their yield, in terms of bioenergy and food crops.
A combination of such genomic improvement might enormously increase the amount of carbon that vegetation naturally extracts from air, according to the authors’ scientific estimates.
When it comes to discourse about genetic engineering, people are concerned about its use in humans, animals, [“Genetically Engineered Salmon Safe to Eat, but a Threat to Wild Stocks, Expert Says”]. Now, the debate is becoming more complex. The chaos of climate change combined with the political chaos of public policy by individual states, nations and global initiatives make the future very sensitive to initial conditions.
Who knows? Someday, humanity+ may walk beneath a canopy of leaves of trees+.