Ann Vole wrote:
Geothermal (the type where you drill down to the hot parts of the earth's crust) is pushed as a great way to reduce the emissions of CO2 and thus global warming. Someone said that it was adding heat to the atmosphere that would not have been added naturally. This is not entirely true in that the heat is in fact heading to the surface which is why we need to drill down so far. We do of course make it easier to get to the surface so that might have an effect but I doubt that volume is much and of course the heat naturally heading to the surface is reduced in the same proportions as the heat extracted. What got my attention though was the plumes of steam that some geothermal operations have from the cooling towers. To make turbines more effective, you increase the temperature difference on each side of the turbines so they spray water on the cooling pipes. The best geothermal locations generally are in places with little water resources so other options are being used (including less efficient turbines). The most influential greenhouse gases is not CO2 but rather water vapor. The difference is that clouds also reflect sunlight and shade the planet and thus counter some or all of their heat capturing effects. This still leaves some doubt in my mind that geothermal is as great a solution to global warming as it is touted to be.
The problem is not that we are adding to much heat to the atmosphere but that we are not allowing the natural heat from the sun to escape as easily due to the addition of greenhouse gases.
The average time for water vapour in the air is about 8 or 9 days before it is rained out. The only way in which the atmosphere can hold more water is by increasing the air temperature. So if we add water vapour to the atmosphere it will saturate the air in that location and prevent further evaporation. Further to that the amount of water vapour from any steam driven generators is tiny compared to that which is naturally produced by evaporation from the oceans. To put this into perspective the worlds oceans on average evaporate a layer of water some 50 ins thick per year which of course comes back down as rain. The greatest man made source of water vapour would in fact be from burning fossil fuels but again is too small a quantity to have any detectable effect on the climate. The exception is jet aircraft which add water vapour to the atmosphere at high altitude where the levels are naturally extremely low.