Global Warming
Certain gases absorb infrared radiation, and thus act as a blanket trapping the heat the Earth receives from the Sun. The four most important greenhouse gases, and their causes, are: Carbon Monoxide — burning fossil fuels, deforestation; Methane (CH4) — solid waste, agriculture, cow farts; Nitrous Oxide (N2O) – smog, chemical fertilizers; and CFCs / HFCs / PFCs—air conditioners, refrigerators, some styrofoam (note this is a separate effect from ozone depletion). This last category (halogenated chemicals – those which contain fluorine, chlorine or bromine), while accounting for the smallest amount of greenhouse gases by volume, is so extremely potent that it is responsible for the vast majority of global warming damage. These chemicals can and should be phased out. All of these are being pumped into the atmosphere at increasing rates; scientists expect a warming of 3-8oF by the middle of the next century. The greenhouse effect is already starting. The fifteen hottest years on record are all since 1980. Effects might include a sea level rise of 1-2 meters, severe droughts and floods, disruption of weather and ocean patterns, etc. More extremes of both heat and cold are expected—so individual cold winters are not proof that the greenhouse effect is not taking place.

The exact effects are highly uncertain—the Earth is full of complex feedback that could make the problem better or much worse. These effects are too complicated to reliably predict—and we have no time to refine our analysis, because the gasses we’re putting in the atmosphere now will affect us for decades to come. We can’t wait to see how it comes out.

Luckily, most of the things we need to do to reduce our output of these gasses are pretty sensible anyway. We need to stop deforestation, ban CFCs, control smog, and reduce our use of chemical fertilizers by moving towards organic farming. Since agriculture, especially livestock, is a major source of methane, eating lower on the food chain and controlling our population would help. Finally we need to reduce our use of energy and switch to alternative sources like solar and wind.