'Green' has to be one of the most overused words there is in today's vocabulary. What does it mean? Green is always good? Bile is green...who wants a big tumbler full? People are said to be green with envy. Is that now a good thing? I am not picking on you; it's just that I can't pick up a newspaper without that word being in the title of a half dozen articles and I'm sick of it. That and the word 'hoops' being used to describe the game of basketball. Rant over, no offense intended, if some was taken, I apologize in advance.
Now, I don't have any scientific data to back this up, but I am going to propose that when you cold-start your diesel and it is emitting white smoke until it warms up.....that you have more than offset the amount of stack-scrubbed, coal-fired power plant generated electricity it would have taken a little block heater to warm your engine to the point that it didn't do that. That white smoke is unburned hydrocarbon fuel...not too Green, you know. Cold starts are probably the primary source of fuel in the oil. And fuel in the oil makes you change it sooner, thus being less (everybody say it with me) Green.