People who minimize or deny the threat of climate change (or ocean acidification, as in part IV of Dr. Everett’s testimony) will often demand that the change be “unprecedented” – that nothing like it has ever happened before in Earth history. (eg, here) The reasoning seems to be that if there have been ecological events like anthropogenic climate change in the past, then current events must not be alarming, since life on earth has each time survived and recovered:
“We know that the Earth has seen these conditions before, and that all the same types of animals and plants of the oceans successfully made it through far more extreme conditions. ” – Everertt (part V)
This has always seemed to me like it’s setting the bar a bit low: Do we only become alarmed when faced with the possibility of sterilizing the planet? And considering the amount of violence which earth life has withstood over the ages, it doesn’t seem a very strong statement that human impact is unlikely to wipe it out.