Without this effect the Earth's average temperature would be about -20o C, compared to the present +20o C (the planet Venus, with a surface temperature of about 450o C, is an example where the greenhouse effect is extreme). However, again mainly from burning fuels (but also from CFCs and their alternatives), it has been recognized that we are adding more greenhouse gases such as carbon dioxide to the atmosphere, which would lead to global warming.
As with the problem of acid rain, the solution to global warming is not so straightforward due to our heavy reliance on fossil fuels. Alternatives such as solar, geothermal, tidal, and wind power and nuclear fusion to generate electricity and battery-operated cars are being developed, but these are not expected to be available on a commercial scale for a few decades, if at all. Compounding this particular problem though is measuring how large an effect it actually is, as there are normal yearly variations in the Earth's average temperature and this effect, if real, would only show up over a larger time scale. As well, some argue that the Earth has a built-in compensation mechanism against global warming, in that increased heat would lead to increased evaporation, which would produce more clouds which subsequently block more sunlight from the Earth's surface. Although more studies of the magnitude of this problem are still being done, it is generally recognized that something should be done even if we don't understand all the details, as if we wait too long it may be too late.
