The state of California approved a bill to reduce CO2 emissions from light duty vehicles sold in the state by 26% by 2016 (approx. 43 mpg). Eleven NE states adopted AB1493. The Alliance for Automobile Manufacturers sued on behalf of automobile dealers in California and Vermont. A trial was held in Federal Court in Burlington VT in April and May 2007. The key issues were (1) is this a mileage regulation (purview of congress) or a pollution regulation (purview of state)? (2) what are the costs involved? and (3) what is the impact on climate? I appeared as the unpaid, expert witness on behalf of the AAM, presenting testimony primarily on the impact of the bill if adhered to by (a) the adoptive states, (b) the entire country and (c) the whole world. James Hansen appeared on behalf of the states. In Sep 2007, the judge ruled the law should stand. Questions of climate variability, data quality, predictive confidence, tipping points etc. were discussed in the courtroom - a very different and highly controlled venue for scientific presentations (the credibility of the witnesses was more prominent than the credibility of the numbers.) The phases of the trial (pre-trial, depositions, reports, testimony, decision) will be described.