That’s it then we are stuck with 400ppm

 According to a new study recently reported in the journal Nature, atmospheric concentrations of CO₂ will stay permanently above 400 parts per million (ppm) this year due to El Nino. The follow on bad news is that the researchers do not expect that it will likely drop below 400ppm "within our lifetimes,"

Commenting on the research presented in Nature the lead author of the study Richard Betts from the UK's Met office said:

"Once you have passed that barrier, it takes a long time for CO₂ to be removed from the atmosphere by natural processes."

"Even if we cut emissions, we wouldn't see concentrations coming down for a long time, so we have said goodbye to measurements below 400 ppm."

The study is based on measurements taken at Mauna Loa Observatory in Hawaii. Scientists first began tracking daily CO₂ levels at the site, which sits atop a volcano, in 1958. The resulting record, known as the Keeling Curve, is one considered a pillar of modern climate science.

For grim reading go to:
http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3063.html#affil-auth