A new 2-million-year history of our planet has some worrying news about the future

Hammock ocean

It isn’t news that our planet’s climate is warming and changing. But a new, 2-million-year history of Earth’s sea surface temperatures offers some alarming insight into what that change could mean over long time spans.

Published Monday as a letter in the journal Nature, it suggests that greenhouse gas emissions released since the Industrial Revolution may already “commit” Earth to as much as a five degree Celsius hike over the next several millennia.

A challenge in building very long histories of our planet’s climate is that it’s impossible to stick a thermometer in the air and know how warm it was 500,000 years ago.

Carolyn Snyder, a Stanford-affiliated climate researcher and a policy director at the EPA, collected 20,000 reconstructions of sea surface temperature from the last 2 million years of Earth history. These reconstructions use a range of proxies, like the density of micro-fossils in sediment from particular geological eras, to estimate changes in temperature over time spans of thousands of years.

The goal isn’t to offer exact weather reports for 783,245 years ago, but to paint with a fairly broad brush a picture of how our planet’s climate has shifted over time.

Snyder compared her findings about how sea surface temperatures have changed to ice core data on the long history of greenhouse gases in our atmosphere. She found that changes in greenhouse gases such as those we’ve already seen tend to associate with temperature increases of about five degrees Celsius over the course of a couple thousand years.

This research matters because it helps us peer into the long future of our planet’s history. Not only does Snyder’s research further back up more immediate work using different methods about how our planet’s climate is changing, it tells us how much it’s likely already changed in the big geological picture. Policy leaders like to talk about holding human-generated emissions within the range of a two-to-three-degree heat hike.

Snyder shows we may have already blown past that mark.

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