01-12-2009, 06:51 PM
David Guyatt Wrote:Everyone: I am a dummy when it comes to technical/scientific details so please treat me gently. It seems evident that global warming is happening over an extended period -- witness to this is that in the mid/late 1800's during winter times people use to light large bonfires on the iced-over Thames and huddle around them (no chance of that today -- too much effluence I guess).
So the question has to be, I suppose, is whether what we are witnessing is a natural warming cycle? After all, the UK used to have a tropical climate in the distant past, so it doesn't seem so odd it could revert to that again.
Children's stick-figure sketches in response very welcome. Anything more complicated gets lost in translation.
I'm no expert of course, but I think you've hit on the crux of the matter, David. It's about cycles. There is general warming because we are coming out of an ice age and are in an interglacial. On the more recent timescale, the Warming of ~AD 1000 gave way to the Little Ice Age when the Thames froze over and fur became a highly valued commodity across Europe. I have an audiobook of Bill Bryson's (probably butchered his surname, sorry) book "A Short History of Nearly Everything" which has a surprising amount of information on the history of geology as well as geological history. It makes plain how many of the divisions into geological ages, eons, epochs etc. were subject to much controversy at their birth, and are, essentially, arbitrary.
The earth has been much warmer before, and much colder. The rule seems to be that the climate is chaotic, and we for whatever reason inhabit the only known period of relatively stable climate changes. There are Great ice ages and Little ice ages, and there are points midway through interglacials when the climate turns cold. The periodicity seems to be 360,000 years and 60,000 years, and some smaller cycle, maybe of 6000-10,000 years, I'm not sure.
http://www.itsrainmakingtime.com/_recent...part1.html has an interview where various people talk about these and other cycles. Half of one equinoctal precession seems to be a key period in earth magnetism, according to one of the speakers.