'In the blink of an eye' Earth's deep history reveals pace of change

Climate records are tumbling at a galloping pace.

- Oliver Milman

The world has just experienced its hottest ever single day on record, amid a string of record-breaking months that followed the planet's hottest recorded year. But how does this cascade of new highs in the era of modern record-keeping compare with the Earth's deeper history?

Those who piece together what past climates were like in eras before thermometers and satellites - a practice known as palaeoclimatology - find that today's temperatures are, when narrowly viewed, unremarkable. For example, the Eocene, an epoch lasting from 56m years to 34m years ago, was "screamingly hotter" than today, by about 10-15C, according to Matthew Huber, an expert in historical climates at Purdue University in the US.

But, crucially, in the timespan in which humans evolved and formed organised societies, today's global climate - a bit more than 1C hotter on average than it was in the preindustrial period before people started burning huge quantities of fossil fuels is unparalleled. It has not been as hot as this for at least 125,000 years, prior to the last ice age, and most likely longer, potentially going back 1m years.

"Humans have not faced a climate like this over our long history; we are starting to hit temperatures that are unprecedented," said Huber. "It's not like we will all become extinct, but we are messing with a thermostat that is pushing [us] outside a window we have been in during all of human civilisation."

The Earth has had numerous climate fluctuations marked by ice ages over its long history but for the past 10,000 years or so conditions have been relatively stable. The agreeable temperature and stable coastlines have allowed humanity to flourish.

"The climate settled on an even keel, people could settle in one place and civilisation started," Huber said.