It comes down to the evolutionary history of Earth throughout life's 4 billion year tenure on this planet. The climate has gone through EXTREME changes [1][2], including the Chicxulub impact, which radically impacted the atmosphere's composition and life on this planet. Yet, the biosphere has always adapted and life continued.

Assuming that mankind is destroying the biosphere at an unprecedented rate (we are), and burning hydrocarbons at an even faster rate (we are), are these two factors enough to turn the earth into a Mars-style wasteland, completely devoid of all life?

It just doesn't seem plausible to me on an intuitive level. We can use linear regression models of the atmosphere and show temperatures rising until life becomes impossible, but that is not how complex biospheres work.

In any case, climate science is definitely a worthy scientific discipline to study, but it is becoming akin to economics in the prediction department. As in, the principles are sound, but the predictions of the experts are laughably wrong on a regular basis.

Unfortunately, this is all due to Al Gore and his "moment of genius" which instantly politicized the scientific process, thereby destroying any potential for real scientific progress through the feedback loop of empirical testing and model formation. If you disagreed with Al Gore's version of climate change, Al Gore's version of climate models, and Al Gore's version of climate science, you suddenly became a heretic "climate change denier".

Alas, we humans really are terrible at science.

1. http://www.biocab.org/Geological_Timescale.jpg

2. http://earthguide.ucsd.edu/virtualmuseum/images/CO2History.h...