We humans always seem to be searching for the Holy Grail, the "magic bullet" that will solve all of our problems, or at least some of them. The funny thing is, in the case of one of our biggest problems today – climate change – we may be onto the path of finding it.
Don't get out the champagne yet, because there's still a huge amount of work to be done, and even if the work is done, there still is no guarantee.
So just what is this veritable Holy Grail for greenhouse gas induced climate change? An artificial leaf, which is being developed by a variety of scientific researchers.
In a sense, we already have the Holy Grail for climate change. It's called photosynthesis. Trees can take carbon dioxide and water and convert them into simple sugars and oxygen. You might even recall the equation for this from high school biology or chemistry:
6CO2 + 6H2O à C6H12O6 + 6O2
A tree can take six molecules of carbon dioxide and combine these with six molecules of water to create one molecule of simple sugar plus six molecules of oxygen. We humans, as well as other animals, expel carbon dioxide with each breath we take. Trees recycle that into oxygen and sugar.
For most of history that process has been in balance. Unfortunately, with the Industrial Revolution the burning of fossil fuels such as oil and gas has thrown more carbon dioxide into the atmosphere than trees can recycle. If we could plant enough trees and shrubs, in theory we could solve the greenhouse gas problem without changing our current fuel use habits. Simon Lewis, a climate expert at the University of Leeds in the UK, observed in 2009 that "tropical forest trees are absorbing about 18% of the carbon dioxide added to the atmosphere each year from burning fossil fuels."
Right now, worldwide we're generating about 40 billion tons of excess carbon dioxide. How many trees would it take to absorb all of that? The average mature tree can absorb about 48 pounds of CO2 each year, and a forest that covers one acre can absorb at 2.5 tons/year. For those of you more familiar with the metric system, one acre is 4046.8 square meters. Thus, if we could plant about 16 billion additional acres of trees, we could absorb the excess 40 billion tons of CO2 each year. This, of course, assumes that we won't keep increasing the amount of carbon dioxide into the air each year. That may be a bad assumption, at least at present, but let's be optimistic for a moment. How much land area would it take to soak up the current 40 billion tons?
- The total surface area of the Earth is 196.9 million square miles
- There are 640 acres in a square mile, so there are 126.016 billion acres of land mass on the Earth
- The required 16 billion additional acres of forest would cover about 12.7% of the Earth's surface.
That's an awful lot of surface area, but actually something that is feasible. Just very unlikely!
If we're not prepared or able to do that, there may a second Holy Grail in the works: the artificial tree mentioned before. Now I'm not talking about the kind of tree many of us decorate for Christmas. This would be a veritable "metallic cousin" to your artificial Christmas tree, just that it would have the amazing capacity to convert CO2 into something else.
Scientists have been working on this technology for a number of years. One place where such research has been underway is Harvard University. In fact, Scientific American and the World Economic Forum named Harvard's artificial leaf as the breakthrough technology of 2017.
Harvard isn't only place where such research is being done. Recently, scientists at the University of Illinois at Chicago (UIC) reported that they had developed an artificial leaf that has two very important characteristics:
- It is about ten times more efficient than an ordinary tree at removing CO2 from the air
- UIC's artificial leaf can absorb CO2 at the level of concentration typically found in the natural environment. It didn't need to be highly concentrated, as for instance from an exhaust pipe of a process plant.
As reported by the University of Illinois at Chicago, Meenesh Singh, assistant professor of chemistry, and his colleague Aditya Prajapati, a graduate student in his lab, proposed solving this problem by encapsulating a traditional artificial leaf inside a transparent capsule made of a semi-permeable membrane of quaternary ammonium resin and filled with water. The membrane allows water from inside to evaporate out when warmed by sunlight. As water passes out through the membrane, it selectively pulls in carbon dioxide from the air. The artificial photosynthetic unit inside the capsule is made up of a light absorber coated with catalysts that convert the carbon dioxide to carbon monoxide, which can be siphoned off and used as a basis for the creation of various synthetic fuels. Oxygen is also produced and can either be collected or released into the surrounding environment.
"By enveloping traditional artificial leaf technology inside this specialized membrane, the whole unit is able to function outside, like a natural leaf," Singh said.
According to their calculations, 360 leaves, each 1.7 meters long and 0.2 meters wide, would produce close to a half-ton of carbon monoxide per day that could be used as the basis for synthetic fuels. Three hundred and sixty of these artificial leaves covering a 500-meter square area would be able to reduce carbon dioxide levels by 10 percent in the surrounding air within 100 meters of the array in one day.
Of course, turning carbon dioxide into carbon monoxide is a "good news/bad news" proposition. Getting rid of the carbon dioxide helps with the climate change problem, but carbon monoxide is bad news, too. The UIC system will have to provide a way to turn that carbon monoxide into a usable fuel, otherwise it will need to be sequestered. The UIC researchers seem to think it can be done.
If the University of Illinois "artificial leaves" are ten times more efficient than natural trees at absorbing CO2, how many would it take to remove the 40 billion tons of excess CO2 presently being emitted each year?
- As mentioned earlier, the UIC researchers reported that a single array of 360 leaves covering 500 square meters could remove about one half ton of CO2 daily, meaning about 180 tons/year
- We would need 220 million such artificial leaf arrays to remove the 40 billion tons of excess CO2 each year (assuming each molecule of CO2 could be converted into one molecule of carbon monoxide (CO))
- The surface area of the Earth is about 510.2 trillion square meters
- The necessary arrays would cover a surface area of about 110 billion square meters, representing 0.02% of the surface area of the Earth.
If the UIC leaves are reportedly ten times more efficient than a natural tree, so it may take about ten times more of these arrays than the above calculations would suggest. If the natural forests would require 12.7% of the land, the UIC artificial leaves may require 1 or 2% of the land. Either way, that's a lot of surface area, but presumably substantially less than the area a natural forest would take to remove the comparable amount of CO2.
Once again, a Holy Grail is possibly in sight, but not anytime soon when you consider what it would take to build all these "natural leaf" arrays. The requisite land is one thing, but the capital cost would be another huge hurdle. Not only that, there remains the problem of converting that carbon monoxide into a usable fuel. This of course begs the big question, who is going to pay for this?
Economists will tell you that this is a perfect application of a carbon tax. The proceeds from such a carbon tax could be used to acquire the necessary land, as well as to pay to construct the artificial leaves.
Once again, don't get out the champagne.
So what conclusions can be drawn from this? If there is no practical way either to get all those natural forests planted, or to get artificial leaf arrays constructed, why pay any attention? The reason is because of the potential for additional research to produce even more efficient natural leaf arrays.
The obvious analogy is to Moore's Law. Back in the mid-1960's, Gordon Moore of Intel Corporation noted that the number of transistors that could be packed on a chip was doubling every 18 or so months. Based upon that observation, made using only a handful of data points, Moore forecast the creation of vastly more powerful computers in just a few years. Moore's Law has continued to work for 50 years! Today's computers can do things only in the realm of science fiction when Gordon Moore first developed his "Law". Moore's "Law" worked because of huge amounts of research done to pack ever more transistors onto a chip.
It seems reasonable to believe something similar could happen with respect to artificial leaves. If the University of Chicago's artificial leaves can operate at ten times the efficiency of a natural tree, is it beyond the realm of possibility that could be increased another ten or twenty fold? Following the logic of Moore's Law, a ten or twenty fold increase would be merely a "warm up". If artificial leaves have a Moore's Law "encore", in about 10 years the artificial leaves developed by UIC will be about 120 times more efficient. That doesn't mean you'd only need about 2 million arrays worldwide, because there's only so much CO2 any given array can pull out. However, a much more efficient array might be able to pull out a high percentage of CO2 exhaust from a power plant. As such, in 10 or 20 years it may be possible to have artificial leaves doing the bulk of removal of excess carbon dioxide. The Holy Grail might then be within our grasp.
Even if a "Moore's Law" solution can only make a given array capable of pulling only so much more CO2 out of the air, it might help reduce the capital cost of the array dramatically, making it much more practical to implement this solution.
Once again, don't get out the champagne just yet. Instead, this suggests that we should pursue a "portfolio approach" to CO2 removal. The various parts of the "CO2 removal portfolio" would include the following:
- More investment in alternative energy
- Additional research into artificial leaf technology
- Additional planting of natural forests
- Additional research into CO2 sequestration technology
- Additional investment in nuclear energy.
The latter has the problem of nuclear waste, so that portion of the "portfolio" might be a bit risky. The key point to make, however, is that just as the pros tell us to make sure we have a diversified portfolio of investments to ensure financial security, we should have a diversified portfolio of investments to deal with the greenhouse gas problem. Additional research into "artificial leaf" technology should be an integral component of the portfolio.
The latest news out of the University of Illinois at Chicago is certainly encouraging. However, the clock is continuing to tick. We don't have enough time to go about the task of greenhouse gas removal at a leisurely pace. Continued investment in alternative energy technology is extremely important. The alternative leaf may be an unexpectedly valuable tool in the fight against greenhouse gases – maybe even a Holy Grail.
