Can we avoid climate disaster simply by cutting back radically on the emission of greenhouse gases? Possibly not, and therein lies a problem. Because of the slow cycle time of carbon dioxide in the atmosphere and the thermal inertia of the oceans, we are almost certain to see a continued rise in temperatures over the coming decades even if we were to stop all greenhouse gas emissions tomorrow. It may well be that a temperature increase of just a couple more degrees is enough to kick off a catastrophic shift in climate systems. A wise strategy for dealing with climate disruption, therefore, relies on drastic reductions in carbon output but would need to include careful efforts to extract carbon from the atmosphere and store it for an extended period of time -- and researchers at the Emory University School of Medicine may have figured out a way to do just that.
We've talked about sequestration a few times here, and always with a skeptical eye. Many of the sequestration proposals are efforts to reduce the greenhouse footprint of otherwise carbon-intensive processes, like energy production from coal. Although it relies on carbon capture technologies, this version of sequestration is just another form of carbon emission reduction, no different (from the atmosphere's perspective) from a shift to renewable energy or higher efficiency use. What I'm talking about here is the active reduction of existing atmospheric CO2 -- intentionally decreasing the concentration of carbon dioxide, not just waiting for it to cycle out. It's another example of Terraforming Earth, but arguably one on the less-potentially-disruptive end of the spectrum.
The Emory University group has figured out a way to boost the efficiency of the key carbon dioxide-fixing enzyme in plants five-fold. The enzyme, known as RuBisCO, is a thousand times slower in its processes than most similar enzymes, and plants have to make a lot of it in order to consume usable amounts of CO2; increasing its efficiency means that plants can take in and use much more CO2. Interestingly, the basic process used by the researchers turns many expectations about biotechnology upside-down: directed evolution:
Dr. Matsumura and his colleagues decided to use a process called "directed evolution" which involved isolating and randomly mutating genes, and then inserting the mutated genes into bacteria (in this case Escherichia coli, or E. coli). They then screened the resulting mutant proteins for the fastest and most efficient enzymes. "We decided to do what nature does, but at a much faster pace." Dr. Matsumura says. "Essentially we're using evolution as a tool to engineer the protein."
Because E. coli does not normally participate in photosynthesis or carbon dioxide conversion, it does not usually carry the RuBisCO [carbon dioxide-fixing] enzyme. In this study, Matsumura's team added the genes encoding RuBisCO and a helper enzyme to E. coli, enabling it to change carbon dioxide into consumable energy. The scientists withheld other nutrients from this genetically modified organism so that it would need RuBisCO and carbon dioxide to survive under these stringent conditions.
They then randomly mutated the RuBisCO gene, and added these mutant genes to the modified E. coli. The fastest growing strains carried mutated RuBisCO genes that produced a larger quantity of the enzyme, leading to faster assimilation of carbon dioxide gas.
This isn't what most people think of when talking about transgenic biotechnology. The plant genes are transferred into E. coli not to make the bacteria into a carbon-consuming wonder, but simply to take advantage of the rapid pace of bacterial reproduction. The scientists can get orders of magnitude more generations of bacteria than generations of plants in the same time frame. The most efficient mutation of the RuBisCO gene can in principle then be re-introduced to the plant species.
It's possible that plants with the mutated RuBisCO gene could be deployed as sequestration groves operating, at least theoretically, at five times the carbon uptake speed of natural species. This could turn tree sequestration from a sideshow to a primary carbon mitigation methodology.
As with other Earth-Terraforming ideas, the proliferation of accelerated-CO2-uptake plants would have to be carefully monitored and controlled. The increased carbon capture rate means faster plant growth; this, in turn, could remove nutrients from the soil or require greater water availability than is sustainable. Ideally, the modified trees would have an "off" switch -- likely an engineered dependence upon a chemical not found naturally in the soil medium, the removal of which would make it impossible for the engineered seeds to sprout.
We will face an unpleasant choice in the years to come: the use of potentially-risky methods to prevent an undeniably catastrophic result. Although the risks from the introduction of accelerated-RuBisCO plants are likely minimal -- after all, the enzyme is a descendant of the naturally-occuring version, not an alien introduction -- the need to reduce global carbon concentrations will probably mean deploying such plants well before we can run life cycle tests. We'd want the sequestration plants to be long-lived, so that their eventual death and decay, releasing their captured carbon, will happen after the immediate threat is long past. This means, however, that we won't be able to see exactly how the lives of these trees change with the new version of the enzyme. Under normal circumstances, we'd definitely want to go through a controlled generation or two before widespread deployment.
Sadly, we're not likely to see "normal circumstances" again very soon.
(Via Green Car Congress)
