Think about that for a moment: even if we eliminate 100% of all carbon emissions today, worldwide ... the existing CO2 in the air will still take us all to a planet where no human being has ever lived.

Determining long-ago levels of CO2 in the air is tricky business. The most straightforward way to do it is with ice cores. As snow falls, it traps little pockets of air that get squeezed down into tiny bubbles within what eventually becomes ice. If that ice is very old -- like in Greenland or Antarctica -- you can open up those bubbles and measure the gases within them directly, from the time when the snow originally fell.

The problem is that even the deepest ice cores in Antarctica only go back 800,000 years. Beyond that, you need to use a proxy of some kind. And up till now, those proxy indicators have been pretty fuzzy.

Author Tripati and her colleagues used the ratio between boron and calcium in fossil shells of formanifera (a type microscopic marine life) as their new proxy. They were able to validate this proxy using the existing well known ice cores during the past 800,000 years, and showed that their technique had an error of only 14 ppm, vastly superior to any previous proxy method.

Then they were able to reconstruct the CO2 levels much farther back using the same proxy. This confirms what most have long suspected: the current CO2 levels are higher than at any time in many millions of years -- long before the evolution of human beings, or of most of the species we rely upon for food.

The good news is, it takes a while for the oceans to warm up. The bad news is, we're not doing anything -- or not nearly enough -- to prevent it.

Abstract from Science Express:

Here.