Earth’s last major warm period was as hot as today

The last time Earth’s thermostat was cranked as high as it is today, sea levels were high enough to completely drown New Orleans (had it existed at the time), new research suggests.

Ocean surface temperatures around 125,000 years ago were comparable to those today, researchers report in the Jan. 20 Science. Previous estimates suggested that this period, the height of the last warm phase in the ongoing ice age, was as much as 2 degrees Celsius warmer.

Climate scientists often use the last interglacial period as a reference point for predicting how rising temperatures will affect sea levels. The new results, the researchers write, will help scientists better predict how Earth’s oceans and climate will respond to modern warming. Warming 125,000 years ago raised sea levels 6 to 9 meters above present-day levels.

The global scale of that warming has been difficult to estimate. Chemical clues inside dozens of seafloor sediment samples collected from around the world provide only regional snapshots of the ancient climate. Combining 104 of these dispersed data points, climate scientist Jeremy Hoffman of Oregon State University in Corvallis and colleagues pieced together a global climate picture.

Average global sea surface temperatures around 125,000 years ago were indistinguishable from the 1995 to 2014 average, the researchers estimate.