To get a full grasp of climate change, you need to take a geological perspective. Wind the clock back all the way through human history, past the Romans and through the Stone Age, to the time before modern humans evolved, and our ape ancestors roamed in Africa.

Roughly three million years ago, in an epoch called the Pliocene, was the last time carbon dioxide levels were as high in the atmosphere as they are now. In other words, today’s CO2 concentrations — at about 410 parts per million — are higher than at any time during the existence of Homo sapiens.

Sea levels were as much as 30 meters higher than now, suggesting that even today’s carbon dioxide levels will be enough to eventually (albeit over many centuries) melt so much ice from the polar regions that all major coastal cities will be drowned.

But it’s the rate of change that is really off the charts, even geologically. Humans are now transferring 10 billion tonnes of carbon from the earth’s crust — in the form of combusted coal, oil and gas — into the atmosphere each year.

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