Geoengineering techniques

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Physical means of amelioration, such as changing the planetary albedo, are the subject of other chapters in this volume and I thought it would be useful here to describe physiological methods for geo-engineering. These include tree planting, the fertilization of ocean algal ecosystems with iron, the direct synthesis of food from inorganic raw materials and the production of biofuels. I will also briefly describe the idea that oceans be fertilized to encourage algal growth by mixing into the surface waters the nutrient-rich water from below the thermocline.

Tree planting would seem to be a sensible way to remove CO2 naturally from the air, at least for the time it takes for the tree to reach maturity. But in practice the clearance of forests for farm land and biofuels is now proceeding so rapidly that there is little chance that tree planting could keep pace. Forest clearance has direct climate consequences through water cycling and atmospheric albedo change and is also responsible for much of the CO2 emissions. Agriculture in total has climatic effects comparable to those caused by fossil fuel combustion. For this reason, it would seem better to pay the inhabitants of forested regions to preserve their trees than plant new trees on cleared ground. The charity Cool Earth exists to gather funds for this objective. It is insufficiently appreciated that an ecosystem is an evolved entity comprising a huge range of species from microorganisms, nematodes, invertebrates, small and large plants, animals and trees. While ecosystems have the capacity to evolve with climate change, plantations can only die.

Oceans cover over 70 per cent of the Earth's surface and are uninhabited by humans. In addition, most of the ocean surface waters carry only a sparse population of photosynthetic organisms, mainly because the mineral and other nutrients in the water below the thermocline do not readily mix with the warmer surface layer. Some essential nutrients such as iron are present in suboptimal abundance even where other nutrients are present and this led to the suggestion by John Martin in a lecture in 1991 that fertilization with the trace nutrient iron would allow algal blooms to develop that would cool the Earth by removing CO2 (see Watson 1997).

Lovelock & Rapley (2007) suggested the use of a system of large pipes held vertically in the ocean surface to draw up cooler nutrient-rich water from just below the thermocline. The intention was to cool the surface directly, to encourage algal blooms that would serve to pump down CO2 and also to emit gases such as DMS, volatile amines and isoprene (Nightingale & Liss 2003), which encourage cloud and aerosol formation. The pipes envisaged would be approximately 100 m in length and 10 m in diameter and held vertically in the surface waters and equipped with a one-way valve. Surface waves of average height 1 m would mix in 4 tons of cooler water per second.

Our intention was to stimulate interest and discussion in physiological techniques that would use the Earth system's energy and nutrient resources to reverse global heating. We do not know whether the proposed scheme would help restore the climate, but the idea of improving surface waters by mixing cooler nutrient-rich water from below has a long history; indeed, it is at present used by the US firm Atmocean Inc. to improve the quality of ocean pastures. The idea of ocean pipes for geo-engineering was strongly resisted by the scientific community on the grounds that their use would release CO2 from the lower waters to the atmosphere. We were aware of this drawback, but knowing that the low CO2 levels during the glaciation were reached when the ocean was less stratified than now, we thought that algal growth following the mixing might take down more CO2 than was released. The next step would be the experimental deployment of the pipes, observations and measurements.

Planting crops specifically for fuel, although sometimes an economic necessity, is a source, not a sink, for CO2. Biofuels might be made green again if sufficient of the waste carbon from the plants could be permanently buried. Thus if any of the ocean fertilization schemes work, their value could be enhanced by harvesting the algae, extracting food and fuel and then burying the waste in the deep ocean as heavier-than-water pellets. This would remove a sizeable proportion of the carbon photosynthesized and place it as an insoluble residue on the ocean floor. The temperature of the deep ocean is close to 4 °C and the residence time of water there is at least 1000 years. The buried carbon would effectively be out of circulation. It might be possible also to bury land-based agricultural waste at these deep ocean sites. This idea may be even more unpopular than the pipes. Critics rightly fear that waste buried in the ocean might be a source of nitrous oxide or other greenhouse gases, but again we may before long reach desperate times; so should we reject an experimental burial of carbon now?

Another amelioration technique is the direct synthesis of food from CO2, nitrogen and trace minerals. When food was abundant, it seemed an otiose proposal, but not now since food prices are rising. Massive crop failure in future adverse climates would give food synthesis an immediately vital role. The procedure for food synthesis would involve the production of a feed stock of sugars and amino acids from air and water as an industrial chemical operation, using either renewable or nuclear energy. This basic nutrient would be fed to tissue cultures of meat or vegetable cells and then harvested as food. Something similar to this kind of synthesized food already exists in a commercial form. It is a cultured mycoprotein product and supermarkets sell it under the brand name 'Quorn'.

Misplaced fear stops us from using nuclear energy, the most practical and available geo-engineering procedure of all; we even ignore the use of high-temperature nuclear reactors for the synthesis of food and liquid fuels directly from CO2 and water.

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