If you can divine historical global temperatures by examining a few tree rings, then you apparently can do anything — or at least imagine you can.
About the 400 ppm CO2 threshold just reached, AZStarNet.com reports:
The speed of the change is the big worry, said Pennsylvania State’s Mann. If carbon dioxide levels go up 100 ppm over thousands or millions of years, plants and animals can adapt. But that can’t be done at the speed it is now happening.
But what plants and animals have gone extinct because atmospheric CO2 went from 280 ppm to 400 ppm? Name one, Mike. And why do plants thrive in high-CO2 greenhouses and then survive when they leave them?