06-16-06I've talked to a few people and I should follow up on the thing I wrote about warming. Obviously I'm no expert on this so you should search around the net, but there's a key addendum I didn't know at the time.
Warming goes faster and faster as I described previously, but over a longer period (thousands of years) another factor kicks in : so much polar ice melts that a layer of fresh water forms on top of the northern oceans. This screws up all kinds of ocean current flow which is complicated and I won't fully go into. Among other things it actually causes the Gulf stream to reverse (!!). Warm water no longer flows north and the caps actually become cooler again. So, even though the Earth overall has warmed, the caps cool again and you have a very extreme state with heat trapped around the equator and cold caps. The ice caps reform and a cooling cycle begins. Now, cooling is also self-accelerating due to various factors, one of which is that ice is very reflective and reduces the amount of solar energy absorbed. A big factor here is that ocean mixing and ocean current changes is a very slow process (it takes thousands of years), while these other factors are much quicker (hundreds of years). The ocean response is a stabilizing counteracting force but it takes much longer to kick in, it's like a weight on a very loose spring - you shoot one way and it takes a long time to repond, then it way overshoots, then it swings way back the other way. Once the earth kicks into a cooling cycle, that's a much more stable state and the earth can stay in an ice age for a long time. The temperate/warming states are very unstable and the temperature can rapidly oscillate until it kicks back into an icy state.
Aside from our contribution to global warming, etc. at some point we'll have to think about the Earth's own natural temperature variations, and if we don't want to live in a drastically different environment, we'll have to do something very major to try to control the climate and keep the Earth in the unstable temperate state we like.