Power plants in Texas put out nearly twice the amount of carbon dioxide as those in Ohio and Florida, the group said.
Nationwide, power plants released 2.6 billion tons of carbon dioxide, or about the amount produced by 449 million cars, the group said. That accounted for 42 percent of carbon dioxide emissions in the U.S. in 2007. In Indiana, power plants released about 132 million tons of carbon dioxide.
The study found 73 percent of emissions came from older coal-burning power plants built before 1980, like Duke Energy's Gibson Power Station in Owensville that began operation in 1975, which the group said is the fourth dirtiest power plant in the United States. Nearly half of the nation's power plants were built before 1980, the report said.
"It's time for the oldest and dirtiest power plants to clean up their act," said Megan Severson, the group's Midwest field organizer. "In order to stop global warming and reap all the benefits of clean energy, we must require old clunker power plants to meet modern standards for global warming pollution."
But Duke spokesman Lew Middleton said it was "misleading" to characterize the Gibson plant as dirty due to carbon dioxide emissions since no technology is available to control that form of pollution. Technology that would allow coal-burning plants to capture their carbon dioxide is still being developed.
Middleton said Duke had invested more than $1 billion to outfit the Gibson plant with scrubbers and other devices to limit other types of pollution such as mercury.
Indiana gets about 95 percent of its electricity from coal-fired power plants.
Environment America said cleaning up aging power plants was critical to stopping global warming, which Indiana University-Purdue University at Indianapolis scientist Gabriel Filippelli said is already affecting rainfall patterns in Indiana.
A global temperature rise of 2 degrees Fahrenheit since pre-industrial times has caused a shift to heavier springtime rains, causing flooding and complicating agriculture, said Filippelli.
Severson urged Indiana Sens. Richard Lugar, a Republican, and Evan Bayh, a Democrat, to support a climate bill now working its way through Congress. The bill calls for greenhouse gases to be cut by 20 percent by 2020, a target scaled back to 17 percent in the House after opposition from coal-state Democrats.
Bayh has expressed reservations about costs of carbon cap-and-trade legislation, and said progress on the issue is unlikely without participation by countries such as China and India.
Lugar has said the U.S. must try to reduce greenhouse gas emissions but that the bill in the Senate and a version in the House would drag economic growth.
Environment America also said the EPA should finalize a proposal to require coal-burning plants and other smokestack industries to meet updated standards when new plants are built or old plants are upgraded.
The group also urged a shift to renewable sources of energy such as wind and solar power. Middleton said Duke also supports development of such resources.