That was debated in Congress and it was agreed that Congress would preempt EPA with a cap and trade program in 2009-10 but that failed so Obama move forward with his first CO2 regs, but they applied only to new permits/new plants.
That set off a bunch of law suits by many, many plaintiffs, which were combined and known as Utility Air Regulatory Group v EPA. As you link shows, the DC Court of appeals ruled for Obama/EPA in 2012. The plaintiffs would appeal that to SCOTUS in 2013 and in June 2014 SCOTUS ruled for Obama/EPA.
About that same time, June 2014, Obama would release his second set of CO2 regs(draft regs) except these apply to existing permits/existing plants. This is known as the Clean Power Plan, mentioned in the article above.
The comment period on this is over and Obama/EPA is supposed to issue the final rule in August, after which many lawsuits will be filed. It will have to go back to SCOTUS, but in the meantime, it will be implemented.