The Environmental Protection Agency took the largest step toward addressing Climate change in its history Monday when it unveiled a proposed rule to slash power sector carbon emissions 30 percent below 2005 levels by 2030.

The proposed rule, which also sets a nearer-term target to cut emissions 25 percent by 2020, is the centerpiece of President Obama‘s climate strategy in a policy arena that those close to the effort say is increasingly looked at as his legacy issue. It also builds on a September proposal to impose limits on new power plants.