In a message dated 1/7/2006 8:09:51 PM Pacific Standard Time, plantlady@beautifulblooms.ab.ca writes: I wonder how much the change in the magnetic poles has to do with our climate changes as well? It certainly can affect global weather patterns, as can a whole range of other phenomena! I recently watched a History channel special: The Big Chill: the Little Ice Age. For some 500 years in the Middle Ages, Europe (and much of the Northern Hemisphere) experienced a period of very cold weather. While there is disagreement about what caused this -- a period of unusually high volcanic activity or major changes in the warm water conveyor in the Atlantic Ocean -- there is no disagreement about the effect. The changes this caused in agriculture, living standards, war, migration, (even some speculation about why Stradivarius violins are the way they are -- formed of harder, denser wood grown in a cold climate), etc., was fascinating to hear and see. What is important is that it seemed to have occurred suddenly and very rapidly (although a mere blink in geologic time, of course!). Wine grapes, for example, (introduced by the Romans) were common in England prior to the Little Ice Age and produced the major beverage of the time -- wine. The extreme cold killed them off causing a major change from wine drinking to beer and hard alcoholic beverages, etc., that could be created from more cold tolerant cereal crops. Cereal crops, the mainstay of the population, were ultimately devastated by both the Little Ice Age and almost continuous warfare. One result was that the heretofore scorned potato became a major food crop because it grew underground protected from weather extremes, as well as being somewhat difficult to destroy/burn by marauding armies. The thriving Viking civilization in Greenland disappeared when the climate became too cold for agriculture and grazing animals. Heavy sea ice stopped shipping to and from Greenland and Europe, cutting off resupply of those colonies causing their extinction. One theory is that of the 400K man army Napoleon used to invade Russia, barely 1% survived to return to France having been decimated by an unusually cold period of weather -- much of it either starved or froze to death, or both. Excavations for a building in Vilnius, Lithuania, uncovered a mass grave of some 3000 Napoleonic troops that died there. How many others never got buried or lie in still uncovered mass graves? The most fascinating theory concerned the warm water conveyor that carries warm tropical waters northward (warming the whole region of the North Atlantic) that gradually cools, increasing in density. This colder, denser salty water sinks at the North end of the conveyor, gradually working its way back to the equator only to rise (to replace the warm water moving northward) again to keep the "engine" of this current functioning. The theory is that the warmer period prior to the Little Ice Age caused substantial melting of the polar ice caps. The resulting flood of fresh water, lighter than salt water, mixed with the saline water on the surface of the ocean, so diluting it that it ceased its former increase in density to the point where it no longer sank to create the southward flow of cold water to the equator to be warmed effectively ceasing the conveyor. There is a great deal of argument today about just what is going on with our climate. There can be no question that it is getting warmer (ever since the Industrial Age) and that CO2 and other "greenhouse" gases have increased in the atmosphere. Whether this increase is a recurring phenomenon and has little to do with the burning of fossil fuels is still being debated. For example, during the Carboniferous Era, CO2 was probably in greater abundance in the atmosphere than it is today. But, then, the composition of gases in the atmosphere was considerably different that it is today. I don't think there is any disagreement that the Earth's ice fields and glaciers are melting. Whether enough has done so to affect the North Atlantic conveyor, for example, remains to be seen and whether that will cause the sudden onset of another ice age is yet to be seen. Perhaps, if another volcano explodes and sends hundreds of thousands of tons of gas and ash into the stratosphere to cut the amount of sunlight reaching the Earth's surface (the explosion of Mt. St. Helens pumped only 1% of the materials that the explosion of Pinatubo blew into the stratosphere!) and that in conjunction with the NA conveyor is speculation, of course, but there should be no doubt about the outcome should both occur . . . Dave Karnstedt Silverton, Oregon