"If we are to save humanity and the planet from the worst mass extinction of all time, worse even than that at the end of the Permian, we must stop at two degrees."

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Something bad happened on both Mars with its dried-up watercourses and Venus with its runaway greenhouse effect. Could something bad happen on Earth too? Our species currently turns row upon row of environmental knobs, without much regard to long-term consequences.

— Neil deGrasse Tyson