Although short-term local measurements of 400 ppm have been recorded previously, this marks the first time since record keeping began that CO2 levels were above 400 ppm globally for a month in March this year.
Passing 400 ppm could be an ominous sign of what might come next — and it sends a clear signal that the world must act ahead of the UN climate talks in Paris this December. Already, deadly effects of climate change in the form of rising seas, monster storms, wildfires, and extreme weather of all kinds are common not an exception.
The safe level of carbon dioxide in the atmosphere is 350 parts per million. The only way to get there is to immediately transition the global economy away from fossil fuels and into renewable energy, energy efficiency, and sustainable farming practices.