“If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from [current levels] to at most 350 ppm.”
Dr. James Hansen
That’s Dr. James Hansen talking, former head of the Goddard Institute for Space Studies. Dr. Hansen is one of the most respected climatologists in the world, and when he says that climate change is incompatible with human civilization, we think human civilization ought to sit up and take notice.
That “350 ppm” is where 350.org gets its name. “PPM” stands for “parts per million,” which is simply a way of measuring the ratio of carbon dioxide molecules to all of the other molecules in the atmosphere. Many scientists, climate experts, and progressive national governments agree with Dr. Hansen that 350 ppm is the “safe” level of carbon dioxide.