Late last month, the Energy Department released new energy efficiency standards for microwaves -- an important but dull rule that didn't raise much attention.

Until people started flagging something really unique.

Turns out, the economic benefits of those microwave standards were calculated using a significantly higher figure for the "social cost of carbon." It was the first time the Obama administration used the new calculations in a regulation -- and it surprised a lot of onlookers who didn't realize the administration had even updated its economic figures on carbon emissions.

The social cost of carbon is a way to calculate the environmental and health damage of one metric ton of carbon dioxide. The original standard, which put the cost of carbon at $22 in 2013, was agreed upon by a dozen government agencies in 2010. But after reviewing the latest science about the growing impacts of climate change, that interagency working group decided in May to significantly raise those costs. According to the new standards, the social cost of carbon is now $36 in 2013, and will continue to rise every year. 

And hardly anyone knew about those changes until the Department of Energy casually slipped the new figures into a press release on microwave efficiency.

"The regulatory impact analysis associated with the rule also incorporates an update to the interagency 'social cost of carbon' (SCC) values, based on the best available science, used to calculate the societal and health benefits of reducing greenhouse gas emissions, as discussed in this year’s Economic Report of the President. The present value of total net benefits from the microwave oven stand-by rule are projected to be $4.6 billion over the next 30 years with the new SCC estimates, up from $4.2 billion with the original estimates for SCC," wrote the department in a press release.

The calculations were based upon new findings about sea-level rise -- which is speeding up faster than scientists expected -- and on the projected cost of adaptation. 

This is a really big deal in the regulatory world.

The economic adjustments in the microwave standard are just a small example of how these calculations could impact new regulations on power plants, automobiles, industrial equipment and everything else that requires energy and creates carbon pollution. 

The most significant -- and most controversial -- impact will be on emissions standards for power plants.

In his State of the Union Address, President Obama promised to use his executive authority to reduce global warming pollution if members of Congress wouldn't use theirs. And with legal authorization to regulate carbon dioxide from power plants under the Clean Air Act, the Obama administration has been working for years on emissions standards for new and existing power plants. (The administration continues to miss deadlines for crafting the rule, however.)

The regulations have come under heavy fire from Republicans and industry lobbyists in Washington who call them part of a "war on coal." These increases in the social cost of carbon, which will make it more expensive for the dirtiest power plants to comply to new rules, may give them another reason to attack the Obama administration's efforts.

Climate advocacy groups praised the changes, saying they show the administration is starting to properly value the impact of global warming.

As the new calculations for pricing carbon are digested by regulators, they will undoubtedly create a more contentious political debate over climate action and new efficiency standards.

And to think it all started with a simple rule for microwaves.