Antarctica melting?

This article refers to the potential collapse of the Wilkins Ice Shelf in Antartica, which may melt once CO2 levels get to 400 parts per million, a level that may be reached by 2050. This may be the best case scenario however as CO2 levels now stand at 385 ppm, and are increasing at around 1.7-2.3 ppm per year approx, meaning 400 ppm could be reached by 2017.... much sooner than suggested..?