As you know, California is all set to implement its tough tailpipe GHG emissions standards — and something on the order of 14 other states are ready to follow suit. All Cali needs is a waiver from the U.S. EPA, allowing it to supersede national standards. It first requested the waiver in Dec. 2005, but the EPA has been dragging its feet ever since, to the point that Gov. Schwarzenegger has threatened to sue.

Lots of political observers expect the Bush EPA to deny the waiver, perhaps based on upcoming boosts in national CAFE standards.

Now there’s a new development that could put Bush in a tight spot. The nonpartisan and widely respected Congressional Research Service has weighed in:

California “appears to have a strong case” in its campaign to secure federal approval to set its own greenhouse-gas controls on vehicles, according to an unreleased report from the Congressional Research Service, a non-partisan body known for its credibility on Capitol Hill.

The report found that the state met all tests in getting a waiver from the EPA to enforce its own standards, including “substantial flexibility” for the auto industry and the use of current technologies to meet the new rules, starting with 2009 models.

California also made a “persuasive case” that it has already been granted 53 waivers under the Clean Air Act, with no rejections, and demonstrated the adverse impact of climate change on the state’s water supply, air quality and overall health, which merit stringent state regulations.

The Congressional Research Service is used by all members of Congress, and its reports are widely cited on Capitol Hill as factual, unbiased and reliable. State officials said the report’s positive assessment of the state’s legal and policy arguments could bolster its case with the EPA.

This leaves the EPA with essentially no justification — beyond the nakedly political — for denying Cali’s waiver.

EPA head Stephen Johnson has promised a decision by year’s end, but Schwarzenegger says he’ll sue if he doesn’t have an answer by October.

As they say in the blogosphere: developing.

Update [2007-9-4 16:8:4 by David Roberts]: More from Warming Law.