On May 9, 2013, worldwide levels of carbon dioxide (CO2) -the chief culprit for global warming- reached 400 ppm at the monitoring station in Hawaii, which sets the global benchmark.

Humans have never been exposed to this level. The last time it happened was at least 2 million years ago, during the Pleistocene Era.

In 1958, when measurements of CO2 were first taken, the concentration was 315 ppm. Today levels are growing at about 2 ppm per year, 100 times faster than at the end of the Ice Age, when they stood at 200 ppm. At that time it took 7,000 years for CO2 to rise by 80 ppm; now, they’ve gone up by the same amount in just 55 years.

The speed of the increase is alarming; when concentrations change gradually, over thousands or millions of years, living organisms can adapt. But not at this rate; already thousands of species of all kinds have become extinct, and animals that can are migrating to higher altitudes and latitudes, seeking refuge from the heat.

The possible consequences are frightening. Sudden, massive changes to the ecosystem on which we all depend are bound to negatively impact our food and water supply and pit some nations against others.