| MadSci Network: Environment/Ecology |
You sound concerned about ice ages. I think I can safely say that no one knows for sure whether or not we are going into an ice age. I think I can further say that you have nothing to worry about. Here's why.
Ice ages are common events in the Earth's recent history (the last several million years). Researchers in several fields believe now that they have a fairly good understanding of some of the major causes of these cold climate events. While some recently obtained evidence suggests that the change between a warm climate and a cold climate can happen suddenly (in less than fifty years), this has not been proven conclusively. If you are worried about giant ice sheets appearing from the north and squishing your house, I wouldn't bother. It's not likely to happen in your lifetime. It takes a long, long time to grow ice sheets on a continental scale.
Some of the possible causes of climate change on the scale of the switch to and from ice ages are the following.
(1) Changes in the amount of energy the Earth receives from the sun (the Solar Constant). This is caused by changes in the orbit of the Earth that happen very gradually over tens of thousands of years. These orbital changes are well understood and are given the name Milankovitch Cycles after the man who studied them extensively. It is also possible that the strength of the sun itself could change. Extremely small changes have been observed, but we have not been able to measure the sun long enough to observe any changes that take a long time to appear.
(2) Changes in the arrangement of mountains and continents on the Earth. We know that the continents shift about, altering ocean and atmosphere circulation and affecting climate. We also know that this sort of thing takes a long time (millions of years).
(3) Major volcanic eruptions could in theory lift a large amount of ash and particles (called aerosols) into the atmosphere. This could lead to the Nuclear Winter effect. In this case, climate change would be sudden, but short-lived. Things would likely return to normal after the aerosols settle back to Earth.
(4) Changes to the atmosphere. (I guess (3) fits in this category.) If something were to happen to the greenhouse gases that keep us at the cozy temperatures we enjoy now, the Earth might cool dramatically. I can't really see a way to get rid of a lot of carbon dioxide and water vapur though. In fact, the greatest problem facing the Earth now may be the rapid increase of greenhouse gases in the atmosphere since the beginning of the industrial age. This increase (of CO2 especially) is believed to have caused a small but measurable increase in the average temperature of the Earth.
The issue of climate change is an important and complicated problem. There are many different effects that all work together to produce the climate we enjoy now. Some of these effects act to cool the Earth and others to warm it. I don't think that we are very close yet to completely understanding the puzzle of climate change.