Earlier this month Stephen Hawking declared: “We are close to the tipping point where global warming becomes irreversible. Trump’s action [withdrawing from the Paris climate accord] could push the Earth over the brink, to become like Venus, with a temperature of two hundred and fifty degrees [Celsius], and raining sulphuric acid." Let’s unpack this a bit, using actual science. The proportion of carbon dioxide in the earth’s atmosphere is currently about 400 parts per million (ppm). The Cambrian ...