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Practical ideas for tackling climate change

I am happy to see the Nature article by Prins and Rayner (see Approach to climate change 'needs radical rethink', 26 October) because the politically correct concentration on the Kyoto treaty has suppressed consideration of many practical ideas that can help us survive. I am working on the following:

1. Pumping cold ocean water up from 1,000 metre depth and distributing it at the surface. I have a very tentative design using one cold-water pipe with two pumping plants, each bringing up five cubic metres per second. We need to upwell about a million cubic metres per second to accomplish noticeable cooling of the ocean surface and the overlying atmosphere. Therefore 100,000 of these pumping stations are required.

Pumping power is derived from the solar energy stored in the ocean surface by means of a heat engine that uses the temperature differential between the surface water and the upwelled water. This ocean thermal energy conversion has been under development for more than 90 years with no real success because the developers have attempted to export net power. Even in the tropical ocean, the temperature differential is so small that the heat engine can just about run itself with enough power left over to support housekeeping functions. Much of the available temperature differential is lost in the temperature drops of the evaporator and condenser heat exchangers. Attempts to export net power increase these temperature drops, leaving less temperature differential for the turbine working fluid, which lowers the engine efficiency and requires excessively large structures.

The upwelling system maximises efficiency by exporting only cold water and the nutrients that are dissolved in it. This enables phytoplankton to increase their food production.

The benefits of cooling and increased primary production are spread over a large population, so the economic model provides no revenue stream to finance the development and operation of the system. So in addition to technical evaluation, we will need to improve the economics. Perhaps sufficient altruism will result from a proper appreciation of the global warming and fishery depletion threats to our collective survival. If the upwelling is done in the Caribbean, there would be economic benefit from the reduction of hurricane potential intensity, as explained in my third point below.

2. Using floating solar collectors to evaporate seawater to increase orographic rainfall.

Australia furnishes an ideal situation because it has a central desert, which heats up by afternoon during most of the year. Heated air, which rises, is replaced by air drawn in from the coast. A mountain range on the east coast causes this ocean air to rise and expand, causing precipitation that provides fresh water to the inland slopes of the mountains. This was a fertile area used for agriculture and water supply, but it is suffering from a drought. A large area of the southeast coastal waters covered with solar evaporator rafts could increase the moisture content of this air inflow and provide needed rainfall.

Of course, it is not easy to maintain a uniform depth of seawater on a solar collector tray that is heaving and tilting in a rough sea. You don't want to be heating some water only to have it slosh out of the tray when it rides a wave before it can evaporate. We will need some pumps operated by a photovoltaic panel to keep the water spread out over the evaporator tray. No battery storage is needed because the evaporator only works when the sun shines. The economic model is better here because the equipment and the benefits are concentrated near the heavily populated capital region of Australia. The development and operation could be supported through taxation.

3. Using ocean turbine arrays in the passages between the Antilles Islands to provide electric power for utility customers and desalination plants on the islands. In addition, the turbine arrays can provide sufficient back pressure to cause some of the water from the North and South Equatorial Current to flow around the Antilles island chain instead of entering the Caribbean sea and passing through the Gulf of Mexico. The outflow from the Gulf is restricted by a decrease in depth and a narrow channel between the Florida coast and the Bahama Islands. The flow in this portion of the path is driven by gravity. Reduction of the flow volume would allow sea level to be lower in the Gulf of Mexico.

My very approximate calculations indicate that extraction of three gigawatts from the current in the Antilles passages would lower the Gulf sea level by one centimetre. The proportionality between power extraction and sea level lowering might hold to greater values.

In addition to pollution-free power for the Antilles Islands, the lowering of the Gulf sea level would benefit New Orleans in the United States, and other cities. Furthermore, the reduction of the loop current transport through the Gulf of Mexico would decrease its direct interference with oil and gas operations in the Gulf, and reduce the amount of warm water accumulated inside the loop and warm-core rings which detach from the loop. Passing hurricanes gain strength from these warm water pockets, so this project would result in some decrease in the potential intensity of hurricanes in the Gulf, which would benefit the oil and gas industry. The economic model for this project looks encouraging.