The...warming before our last ice age was much warmer than anything we've had since. We had a warming that peaked 9000 years ago, another warming that peaked 5000 years ago. Both were warmer than today. Probably the Roman warming and the medieval warming were both warmer than today -- and we've had 8 warmings of the earth since the last Ice Age.
So how can we, given our limited knowledge of how the climate works, attribute the extremely limited amount of warming we experienced over the last century to mankind? The honest answer is: We can't.
The earth was cooling from roughly 1940-1976: Despite the fact that widespread industrialization was occurring during that 30 year time period, temperatures dropped so much that there were claims we were going into a dangerous period of "global cooling." If global temperatures are tightly bound to man-made greenhouse gasses and those gasses were being rapidly introduced to the atmosphere, then the earth should have been warming, not cooling during that period. The obvious conclusion is that global temperatures are not nearly as closely associated with man-made greenhouse gasses as some people would have us believe.
So, if it's global warming, why isn't there any warming occurring now? One of the many revelations from Climategate is that behind-the-scenes, scientists who buy into man-made global warming are admitting what skeptics have been saying publicly for years now: The globe has been cooling since 1998. Again, if global warming has its bootlaces hitched to the amount of man-made greenhouse gasses that are being produced and those numbers are increasing, why hasn't the temperature gone up as well? There's a simple answer: Man-made greenhouse gasses are not a decisive factor in raising or lowering the temperature of the earth.
Climate models can't accurately project the weather 100 years in the future: The truth is that we don't fully understand how our planet's climate works and thus, our climate models don't work very well. Since the climate models can't explain the climate over the last 25 years and they can't explain the leveling off of temperature since 1998, why would anyone believe they can predict conditions in 100 years? As computer programmers say, "garbage in, garbage out."
The Doomsday predictions from global warming alarmists are absolutely meaningless because they're based on climate models that don't work very well in the first place. As Dennis Avery, co-author of Unstoppable Global Warming: Every 1500 Years has said:
I think they pull their predictions out of their hats and I don't think they have any validity whatsoever.
What the global warming alarmists are asking of people is no small thing. They want us to spend trillions of dollars, dramatically impact our economies, and change the way people across the world live for the worse. Those are not trivial changes and simply having scientists -- who've been put under enormous political pressure and make a living off global warming grants – say, "Trust us, it's real," isn't going to cut it for proof. If global warming alarmists can't even deliver plausible answers to the most obvious problems with their theory, then no one should take them seriously.