The U.S. Court of Appeals for the District of Columbia Circuit could issue a decision any week now on four related challenges to the steps U.S. EPA has taken to limit greenhouse gas emissions.

The court issues its decisions between 10 and 10:30 on Tuesday and Friday mornings. It is expected to rule on the greenhouse gas cases, which were argued in late February, before its summer break.

The environmental community is waiting with bated breath to see whether the court will strike down some part of EPA's regulatory framework for carbon.

"The anxiety is pretty ever-present given the stakes," said Vickie Patton, general counsel for the Environmental Defense Fund. "There's so much at stake."

But Patton expressed confidence that the court would uphold EPA's actions.

"They are entirely anchored in the law and the science, and we expect that the D.C. Circuit will affirm these landmark policies," she said.

The court is considering challenges to EPA's 2009 finding that carbon dioxide endangers public health and welfare, which forms the basis for all the agency's carbon rules.

Also at stake are the agency's rules for tailpipe emissions from vehicles and permitting requirements for large new and expanded industrial sources.

EPA's tailoring rule, which limits regulation to the largest industrial emitters of carbon dioxide, is considered the most vulnerable to legal attack. The Clean Air Act lays out a threshold of 100 or 200 tons of emissions per year, but for carbon dioxide, EPA effectively changed that threshold to at least 75,000 or 100,000 tons per year, depending on the source.

Natural Resources Defense Council's David Doniger said in a message to reporters today that he expects the tailoring rule to be upheld.

"The challengers are unlikely to get anywhere with their complaint that EPA focused the permitting requirements on the biggest new and expanded industrial sources, and excluded small businesses and small structures like apartment buildings, hospitals and churches," he said. "To have standing to complain to a court, you have to show how you are harmed by the regulation, and how you will be helped by a judicial remedy."

The three judges who heard the case indicated that none of the challengers showed that excluding smaller sources had hurt them, he said.