According to the Oxford Dictionary, alternative energies are energies “fuelled in ways that do not use up natural resources or harm the environment.” Using this definition, there are some apparently environment friendly forms of energy which can’t claim they don’t harm the environment.
Just consider bio ethanol. It promised to reduce the independence on oil imports, to reduce CO2 emissions and more money would flow to farmers rather than to oil sheiks. But obviously, bio ethanol does neither reduce the dependence on oil imports nor does it decelerate global warming. Producing bio ethanol out of corn requires according to a study by the University of California in Berkeley 29% more energy than the fuel later contains. Besides, the production of biofuels harms the environment by converting vast areas of rainforests and grassland into fields for planting crops. Moreover, crops used for biofuels which could also be used to feed people contribute to the global food crisis. Food should not be in competition with biofuels as rising prices result in violence and starvation in many Third World countries.
In the US, bio ethanol accounts for about 5% of gasoline. In Germany, the proportion of biofuels in gasoline was planned to be increased up to 10% by 2009, but luckily the government recently decided to abandon this plan. Most of the biofuel would have been imported from Brazil where crop plantations for biofuels definitely threaten the rainforest which is of much greater use for the global climate than any form of alternative energy.
As most alternative energies lack of efficiency, the most reliable measure to conserve the environment is to increase the efficiency of our energy use and to save energy.