Since I like to piss off both fringes.....

I worked in uncontrolled locomotive emissions so thick they formed nitric acid at Taylor Roundhouse and you had to cover you cars to keep it from eating the paint off at night, and we were breathing that crap. I do believe in modern math and science, and have seen the data, so I think the observed change in atmospheric CO2 level, global temperature, and sea level rise, do seem to have a good causal theory, based on sound physics, and a nearly perfect correlation to the massive growth in humans burning carbon rich fossil fuels.

I also must look at controls for these "externalities" based on the same view of the available economic science, and the current cost benefit of going beyond Tier 4 for health standard pollutants gets pretty far out there, marginal cost/marginal health benefits from this source, in total NOx and Ozone formation (to achieve "breathable" air health standards). And, as to reducing human caused CO emission, there are way cheaper tons of human caused CO2 to buy, compared to the cost per ton you would spend to effectibely electrify the railroads to achieve the same reductions....so it's not exactly "low hanging" fruit".... America, sill has yet to replace 90% of its light bulbs with LED's, which save every person the value of the bulb in the first year from energy savings alone.

I've worked with CARB, and this agency has a difficult job, made more difficult by the problem of "federal" sources (sources of emissions that can only be regulated by the US government, usually due to interstate commerce issues). So I don't think this is "real", either. It's just a "shot across the bow", to set up a challenge, if the EPA attempts to back off of current locomotive standards (like Brown just did on delaying truck emissions deadlines, to get trucker support on the Gas tax bill).

It's good old fashioned bureaucratic/political posturing....."a sound and fury, signifying nothing....", or to paraphrase from the movie Casablanca: "I'm shocked to see gambling going on in this casino...."