At the same time as agreements like the Kyoto Protocol are being debated and signed, climatologists are studying ways to limit global warming.

Continued global warming could have very damaging effects. With C02 playing such a large role in this problem, steps to reduce its levels must be taken urgently.

Two things can be done: either carbon dioxide must be prevented from entering the atmosphere, or the C02 already there must be removed.

The Alternatives

1. Machines called wind turbines can convert wind energy to electric energy.
2. Solar cells can convert sunlight to electric energy, and various devices can convert solar energy to useful heat.
3. Geothermal power plants convert energy in underground steam to electric energy.

Unfortunately, these alternative sources are much more expensive than fossil fuels, and so are impractical for poor industrial countries. However, increased research into their use would almost certainly reduce their cost.

Increased fuel efficiency.

It's not too hard to see how much CO2 emissions are produced by cars and trucks. If you live in a big city, chances are your sky during the day isn't the cleanest or clearest. These polluting emissions could be greatly reduced if cars and trucks could use fuel more efficiently.

To this end, some scientists and engineers are working on engines with improved fuel efficiency. Others are developing replacements for fuel-burning engines, or to use with smaller engines. Cars labeled hybrids have already entered the market. A hybrid has everything a battery-driven electric car has, plus another power source, usually a small gasoline engine. In the future, fuel cells, which can convert chemical energy to electric energy, may be used.

Underground or underwater storage This would involve injecting industrial emissions of CO2 into underground geologic formations or the ocean. Suitable underground formations include natural reservoirs of oil and gas from which most of the oil or gas has been removed. Pumping CO2 into a reservoir would have the added benefit of making it easier to remove the remaining oil or gas. The value of that product could offset the cost of sequestration. Deep deposits of salt or coal could also be suitable.

The oceans could store much CO2. However, scientists have not yet determined the environmental impacts of using the ocean for carbon sequestration.

Storage in living plants.

As they grow, green plants absorb CO2 from the atmosphere. They combine the carbon from this with hydrogen to make simple sugars, which they store in their tissues as food. Ecosystems with abundant plant life, like forests and even cropland, could tie up much carbon.

However, when these plants die, their bodies decay and release CO2 again. It is up to us and future generations to keep the ecosystems intact. Otherwise, the sequestered carbon would re-enter the atmosphere as CO2.