The whole website 350.org was created what now... 6 years ago? Because Bill McKibben said that 350 ppm CO2 was a "safe upper limit" for CO2 in the atmosphere in 2007.
Since we are now well past 350ppm CO2 in the atmosphere: http://www.esrl.noaa.gov/gmd/ccgg/trends/
The IP-Cry-Wolf organization has to create a "new" upper limit. It's just more bullshit. They have no idea what any "safe upper limit" for CO2 is, they guess and publicize scary numbers every 5 years in order to secure future funding.