According to our most recent data, the climate has changed dramatically since last Tuesday. UN Conference on Climate Change
OK, once more, the rate of change is an important factor. Yes, climate has always changed but usually at a much slower rate which allows for biological accommodation. When rapid change has occurred, major extinction events happen, the worst one being the Permian in which some 95% of terrestrial species and 70 % of marine species disappeared, and that was over a time period of about 20,000 years (http://news.mit.edu/2011/mass-extinction-1118). Compare that to the rate of change we are seeing now occurring over a period of maybe 200 years which is unequivocally driven by human activity (https://en.wikipedia.org/wiki/File:T_comp_61-90.pdf). That’s change at a rate 100 times faster that the Permian Great Dying.
Bottom line: If we don’t change our activities we’re gonna be toast—literally.