Uncharted territory: Carbon dioxide expected to peak at levels last seen during Pliocene Epoch
In May 2013, the amount of carbon dioxide in Earth’s atmosphere hit a previously unthinkable milestone.
For the first time in human history, the concentration of carbon dioxide in Earth’s air reached 400 parts per million (ppm). The last time the planet experienced such high levels of the greenhouse gas was more than 3 million years ago, when conditions on Earth were unrecognizable from today and giant camels roamed a mostly ice-free High Arctic.
But what was once seen as an alarming threshold has now become business as usual.