Maryland and eight other Northeast states are moving to crank down on climate-altering emissions from power plants, aiming to lock in and continue reductions that have already occurred over the past several years as a result of coal-burning plants switching to natural gas, a weak economy and improved energy efficiency.

The Regional Greenhouse Gas Initiative, in which Maryland is a participant, announced this week it is lowering its overall cap on power plants' carbon-dioxide releases by 45 percent, to 91 million tons.  The multi-state compact also plans to keep reducing the cap by 2.5 percent a year until 2020, by which time it projects emissions to be half what they were in 2005.

Under the initiative, states since 2008 have been auctioning off emission "allowances" to power plants, requiring them to pay for the carbon dioxide they release into the atmosphere.  Until this year, the cap was loose, but emissions declined anyway.

In Maryland, carbon emissions from power plants subject to the greenhouse gas initiative declined from 35 million tons in 2006 to 22 million tons in 2012, according to figures supplied by the Maryland Department of the Environment.  Greenhouse gas emissions from all sources declined in Maryland, as they did nationally, during that period.

The