It was a geniune question not a bolshy stw I think you're wrong statement. Really, I'd like to read about it.
couldn't pull up an article on it, just something someone at work mentioned and I've no real reason not to believe it, refining diesel is much more energy intensive than refining petrol, here's the pocess simplified
Petrol:
Crude->[atmospheric distillation]->naphtha->[hydrotreater]->[splitter](just another distillation column)
heavy naphtha and light naphtha are then treated by isomerisation and platforming and blended to make the various grades of petrol.
All in all its mainly low pressures and temperatures, nothing too extreme.
Diesel, some of it comes out the atmospheric column, but no where near enough, so you take the heavy fractions and 'crack' them to make lighter stuff, depending on the market this usually means diesel (in America they use FCC reactors which produce more petrol). This involves seriously high temperatures and pressures and lots of energy.
Obviously the carbon footprint of your diesel depends on the oil used in the refinery, the refinery configuration, and the market demands.