What two million years of climate history tells us about the future

Climate science has received a massive boost with the recreation of Earth’s climate history for the past two million years – the longest continuous timeline to date. But the data forecast a grim global temperature rise of at least 3 °C, and as much as 7 °C, if greenhouse gas emissions aren’t reduced.

Pieced together by climate scientist Carolyn Snyder from Stanford University in the US and published in Nature, the timeline is expected to provide insights into some of Earth’s climate mysteries.

While previous climate records only covered smaller portions of time, Snyder’s reconstruction spans ice age cycles without interruption, capturing the peaks and troughs of global temperature movement over the years.

The record compares the global average temperature with other important climate variables: temperatures of the poles, carbon dioxide levels and oxygen levels at the bottom of the sea.

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Snyder writes that the results suggest that stabilisation at today’s greenhouse gas levels may already commit Earth to an eventual total warming of up to 7 °C over the next few millennia as ice sheets, vegetation and atmospheric dust continue to respond to global warming.

So where is two million years’ worth of climate data found?

Snyder analysed 59 slices of sediment drilled from the ocean floor. They offer a glimpse into the past, where chemical clues to prehistoric climate changes exist in each layer.

From these slices, 20,000 sea surface temperatures were reconstructed, equipping Snyder with the tools to create her timeline.

Palaeoclimate scientist Russell Drysdale from the University of Melbourne in Australia, who was not involved in the study, says even a 3 °C rise – the lowest temperature rise this record has predicted – will see sea levels rise six to nine metres.

“Scientists are doing their best to produce science, but it’s up to the population at large who are the consumers, and the politicians who set the boundaries and laws to force change,” Drysdale says.

“We just have to force large scale change in the way we conduct our lives.”

Snyder’s study not only helps predict the future of climate change, it also begins to explain why ice ages changed from occurring every 41,000 years to every 100,000 years.

In her paper, Snyder suggests global cooling – which stalled about 1.2 million years ago – was a condition for the shift in ice-age cycles rather than the sole cause.

“It’s an impressive single-author paper and a massive amount of work for one person,” Drysdale says.

He adds the timeline gives the wider community a new reference curve to frame their own records and will help refine climate models.

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