I am surprised that so many fine scientists are stampeded into saying humans caused global warming. I wonder who was the blame when the various ice ages ended -- did some poor Neanderthal family burn too much firewood while shivering in the cave? Those bonehead! The cry goes out that global warming is causing the Arctic tundra to thaw, releasing greenhouse gases that were locked in frozen vegetation. But where did that vegetation come from in the first place? Also, I have seen estimates of an average difference of half a degree per century attributable to global warming. How does one half a degree either way make any difference to the ice sheets? How many centuries has this been going on to make a significant difference? Do we attribute human-caused global warming to the thaw that allowed the Vikings to settle Greenland? Who was to blame when the climate got colder again? I have yet to see a convincing explanation of how civilization is doing all this. At one time after life emerged on Earth, an event called "Snowball Earth" took place. That is, our planet froze over completely. But somehow, it thawed. Maybe some microbe burned too much firewood. Or just possibly a great period of volcanism put out so much smoke and ash that it covered the ice and snow, and the dark material absorbed a lot of sunlight. Concerning our present warming cycle, I bet periodic changes in volcanism has a big role to play. Has any scientist come up with a volcanism budget? That is, weighed how much carbon dioxide and other greenhouse gases are expelled by huge volcanic explosions? Time and again, we see humans giving themselves far too much credit for long-term changes, good or bad. I think Nature is far stronger than tiny man. -- Joe B.