Solving the CO2 conundrum through charcoal burial

This document is hereby released into the public domain.

Ari Hypponen

Puruvesi, Finland, June 2009


The planet is fine, but it might shake us off like a bad case of fleas

The geologic record shows that the current balmy temperatures on Earth can change abruptly. There is compelling evidence that the planet has experienced sudden hothouse periods with global temperature increases of 6 degrees centigrade or more, and also super ice ages when all the oceans and the whole land surface of the planet have frozen to temperatures around 50° C below zero.

The global thermometer that usually keeps the planet’s temperature in check works through greenhouse gases, primarily carbon dioxide. These gases keep the planet warm by reflecting some of the heat radiated by the oceans and continents back to Earth, instead of letting the warmth escape to space. This greenhouse effect is what makes the planet habitable to us -- without it, the planet would freeze to a snowball.

Unfortunately, the balance of the radiation budget is very delicate, and a sudden introduction of superfluous greenhouse gases will make the whole system go haywire. It is a testament to our ignorance that this is exactly what we have accomplished. During the 20th century humankind developed machines to dig up huge amounts of coal, oil and other fossil fuels, and promptly released the carbon locked in these minerals into the atmosphere. The resulting human-induced CO2 pollution has started heating the atmosphere rapidly, and will continue to do so to the foreseeable future.

What makes this development particularly worrisome is the risk of kick-starting run-away warming through self-feeding processes which, when started, continue to accelerate in a vicious cycle. Several such positive feedback processes are known: melting of sea ice and glaciers expose bedrock and water, which absorb the warmth of sunlight approximately ten times more readily than high-albedo snow and ice; melting of permafrost in Arctic regions releases methane, which is a greenhouse gas 20 times more potent than CO2; and degassing of clathrates, i.e., methane ice deposits on the ocean floor, can potentially result in huge methane burps that would greatly accentuate the warming trend.

The risk of run-away warming can only be avoided by a swift reduction in CO2 production, which means that we will have to stop burning fossil fuels in our cars and power plants. Unfortunately, even complete success in this huge endeavour would be unlikely to be enough to let humanity duck climate change.

We already have an excess of approximately 100 ppm of CO2 in the atmosphere, which is enough to warm the planet by at least 2° C during this century, and probably more. This will result in large changes in weather patterns, with many densely populated areas of the world becoming inhospitable to humans. It would therefore be important to find a way to not only stop the production of greenhouse gases, but also to start the removal of the excess CO2 that is already there.


Learn from the master: enter Mother Earth

Several carbon capture and storage technologies have been proposed to help us release less CO2 from power plants or even to scrub the gas from ambient air. The problem with these technologies is that of scale: the carbon dioxide produced by burning carbon weights 3.7 times more than the original carbon, and, obviously, takes several times the volume even if liquified. We simply would not have enough space in the proposed underground storage for all the CO2 if we managed to capture it. Indeed, it would be much easier and cheaper to not dig up and burn carbon in the first place! CCS is at best a theoretical mitigation approach and at the worst case will divert our attention in the wrong direction until it is too late.

We should not abandon hope, though, as we can learn from the master: the planet has on its own succeeded in controlling the amount of CO2 and keeping the global thermostat steady for millions of years. Carbon is naturally removed from the atmosphere by two processes, namely the photosynthesis in plants and the natural erosion of rocks. The latter is based on weathering of certain minerals, which consumes carbon dioxide, primarily through CaSiO3 + CO2 CaCO3 + SiO2. Carbon bound to weathered rocks is however buried by very slow geological processes: rock erodes in the presence of water, rivers transfer the resulting oxides to continental shelfs, and subduction moves the material to Earth’s mantle. These processes work over geological timescales, so they will not help save humanity from the imminent danger of climate change.

Photosynthesis works much faster and therefore looks more promising. Together, the world’s plants, algae and cyanobacteria remove some 385 gigatonnes of carbon dioxide from the air every year, which is almost 20 times the amount that humanity releases by burning fossil fuels. These photosynthesizing organisms are indeed by far the most efficient geoengineers to bind carbon, and would clearly outperform any high-tech solution we could put together. The problem is that 99% of the carbon dioxide pumped out of the atmosphere by the biosphere is released back to air within a year through decay. The silver bullet to solving the carbon sequestration conundrum is within reach if we can only find a way to inhibit some part of this natural decomposition process.

One surprisingly simple method of accomplishing this has been repeatedly proposed by James Lovelock, the British scientist well known for his Gaia hypothesis and for being the first to detect the widespread presence of ozone-destructing chlorofluorocarbons, or CFC gases, in the atmosphere. He suggests that we should get farmers globally to collect their crop waste and burn it at low oxygen levels, which would turn the carbon compounds in the crop waste into non-biodegradable charcoal. This biochar would then be ploughed into the fields as a soil improver.

Biochar differs from normal biomass in that it is not readily consumed by bacteria or other organisms. Instead, it stays put in the ground, binding its carbon there indefinitely. This tilts the carbon cycle balance, resulting in slow pumping of CO2 out of the atmosphere, which would eventually restore it close to pre-industrial levels.

This scheme would not necessarily require subsidies as the biochar would in itself be valuable -- there are several companies whose business is in improving poor upper layers of earth such as tropical topsoil with it. Ancient South-American, African and European cultures already knew how to engineer this “terra preta” as it is known in Portuguese. In addition, one by-product of the combustion process is a liquid biofuel that could be sold for profit.

So, the question before us is not about finding a way to save the planet -- we already know how to do it, and our ancestors knew it too. The question is about will, and about execution. I hope that the 21st century will prove humanity better than the 20th.



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