Atmospheric CO2 concentrations a thousand years ago were higher than it is now. It was also higher during the time of the dinosaurs. Increased carbon in the environment caused numerous adaptations in living things.. plants grew faster and bigger.. marine crustaceans grew thicker shells, etc.

In short, nature always compensates. There are always millions of feedback mechanisms that we do not know about. Up till today, climate modeling scientists are constantly tweaking their feedback mechanisms. We can't even model clouds and precipitation properly yet, and climate models of carbon sinking by limestone and soil is still pretty poor.

On an almost weekly basis, there'll be news about discoveries of new feedback mechanisms, or corrections to the common wisdom of known climate models' feedback mechanisms.

Personally, I think Anthropogenic Global Warming (aka Al Gore Warming) is terribly overblown and the standard IPCC models have "bad science" written all over them. There has been a lot of fear-mongering, ranging from the melting of the Antarctic or the Arctic ice shelves, to runaway greenhouse effect catastrophes.

Global warming alarmists are beginning to sound like the Jehovah's Witnesses. They keep shifting their doomsday prophecies further back. When a model's prediction failed, they'll cook up another excuse and another story. Well and fine, because that's what science is about, always discarding the wrong theories and coming up with more accurate and refined theories. But the problem is, with so many information gaps, how can we say 100% for certain that increased carbon output will lead to further warming, and further warming will cause catastrophes?

The global warming alarmists didn't even see last winter coming. It was the coldest winter in more than a decade. And they didn't even see the extra El Nino forcing coming up early this year. Neither did they even had any clue that the Earth's orbit eccentricity and tilt with respect to the Sun creates 10,000-year variations in global climate, which was only discovered last week.