Carbon emissions have fallen even as the economy has improved since the recession, according to a new report, bucking historical trends as well as arguments by opponents of President Obama's environmental and climate regulations who say the administration's policies would crimp the economy.

The unlinking of economic growth and emissions increases was a key takeaway in the report, said Dan Bakal, director of electric power with business sustainability group Ceres, which helped craft the annual study. So too were overall emissions declines in regions that have criticized regulations such as the proposed Environmental Protection Agency rule that would set carbon limits for power plants.

"You see some pretty consistent declines in areas like the Southeast and the Midwest," Bakal told the Washington Examiner. "It makes the case that more is achievable."

While the report demonstrates that electric utilities and states are already pursuing emissions reductions on their own, their pace is not aggressive enough to avoid locking in some of the effects of climate change, which most climate scientists say is largely caused by burning greenhouse gas-emitting fossil fuels.

The report, which was led by M.J. Bradley & Associates with assistance from Ceres, Bank of America, electric utility Calpine, the Natural Resources Defense Council and others, surveyed the top 100 electric utilities by generation, which covered 85 percent of the nation's electric power and 87 percent of the industry's emissions. It comes as the Tennessee Valley Authority, the government-run utility and sixth-largest emitter, announced a long-term plan Monday to add more renewable energy and natural gas by 2033.

While overall carbon emissions are above 1990 levels, a combination of the recession, falling natural gas and renewable energy prices and environmental regulations have pushed emissions downward in recent years. Between 2008 and 2013, power plant emissions fell 12 percent. Bakal said lower electricity demand accounted for about half of the initial carbon emissions drop in the first two years after the recession, but the other factors have kept emissions levels basically flat for the past two years even as the economy has grown, the report said.

"Even while we've seen some pretty solid economic growth for a while now, emissions have continued to decline," Bakal said.

Emissions levels in recent years have fluctuated based on how much power plants use coal, which is twice as carbon dense as natural gas. As natural gas prices trended rose in 2013, more utilities turned to coal and emissions rose 2 percent between 2012 and 2013, according to the EPA.

Although carbon emissions have increased from 1990, emissions of mercury, with a 74 percent drop, and sulfur dioxide (80 percent drop) are lower. And the emissions rate of utilities — pounds of carbon dioxide emitted per megawatt-hour of electricity produced — has decreased since 2000 as companies have shifted away from coal and boosted energy efficiency.

That has significant implications for the EPA's Clean Power Plan. The proposed rule sets targets for states to reduce their electric fleet's emissions intensity, which the agency says can be accomplished by improving power plant efficiency, shifting from coal to natural gas, adding renewable power and bolstering customer-side energy efficiency.

Duke Energy, the largest electric power company in terms of generation, underscores the development of utilities becoming more efficient.

The company uses the second-most coal in the country and produces the most carbon emissions from coal than any other utility — its carbon emissions "increased dramatically" since 2000 because of its mergers with coal-heavy Cinergy in 2006 and Progress Energy in 2012, the latter of which boosted the company's total generation by 60 percent.

Yet the company's carbon emissions intensity has risen just 10 percent, which the report partially attributed to "an increase in low- and non-emitting generation."

While Duke's emissions rate has increased, the bump is far less than the relative size of coal-fired generation it added to its fleet. At the same time, other coal-heavy stalwarts have shaved emissions. Southern, which at one point was almost synonymous with coal, has slashed its emissions rate 31 percent since 2000 as it shifted toward natural gas. Similarly, NextEra's emissions rate has plummeted 46 percent.

But it's not all rosy for utilities looking to slash carbon to comply with the power plant rule, which is due for finalization next month. Bigger utilities are large enough to make improvements to their fleets, and the state utility regulators who govern rate increases needed to pay for new investments might be forced to approve projects so states can meet the EPA rule.

Electric cooperatives, though, are a different story — and they're in a precarious position, as the report showed. Of the nine utilities with the highest carbon emissions intensity, seven are electric co-ops. Co-ops are small utilities that are owned, financed and operated by communities and exist largely in the West and in rural locations.

Co-ops have a difficult time paying for upgrades and have largely resisted the proposed power plant rule. Its trade group, the National Rural Electric Cooperative Association, is advising its members to tell states to submit a compliance plan to the EPA that would seek emissions cuts only through improving power plant efficiency. The group contends that is the only measure under which the EPA has authority to require cuts.

Bakal said that reducing the emissions rate at co-ops would be challenging. However, they're not large producers of electricity, as the biggest emitter was ranked 38th for overall emissions. That means states might be able to craft compliance plans that inflict less pain on them.

"There's still a lot of different options there. So some states will encourage increased energy efficiency and some will encourage solar or community solar ... they may look at options for trading either within or between states," Bakal said of states with a large presence of co-ops. "In some cases it could mean decreasing the utilization of some plants."