No one can answer it precisely or with absolute certainty, but we can at least make quantitative estimates about some of the impacts. (Lorry knose, nobody’s requiring any precise or absolutely certain answers from you or Starving Artist in this thread either.)
For example, since there are 600-some coal-fired electrical plants in the US already, if we added 20 more, we should expect the addition (ceteris paribus) to produce about a 3% increase in the climate impacts of US coal-generated electricity in general. Now, since coal-generated electricity plants produce about one-third of all US CO2 emissions (or about 5% of global ones), that 3% increase works out to something above 0.1% of global CO2 emissions, which certainly isn’t very big but it’s not zero either. This article in Atmospheric Chemistry and Physics discusses the net climate impact of coal-fired power plant emissions, which not surprisingly is extremely complex. If we use the 0.1% of all global CO2 emissions as a rough ballpark figure for the contribution of those 20 power plants, and if total emissions were to continue at present levels into the medium term (which they’re unlikely to be, but unlikely to be orders of magnitude different, either), then we could very approximately estimate that the contribution of those 20 power plants to climate change would be about a thousandth of the total CO2 emissions climate impacts. So, very imprecise approximation, but probably not bad as an order of magnitude.
(And I should note that of course none of that takes into account climate impacts from actually getting the coal, just the CO2 emissions from burning it.)
[QUOTE=octopus]
The most one can say is it adds CO2 to the atmosphere.
[/quote]
Specifically, about 2 pounds of CO2 per kilowatt hour.
See, octopus? Quantitative estimation isn’t really so scary or so unattainable! Come to the dork side and join us in our rational quest for realistic information! 
[QUOTE=octopus]
Same thing with people hustling for work. We know that it adds wealth and income. How much? No one can know.
[/quote]
:dubious: Really? Once again, no one can know with absolute certainty and precision, but that’s not the kind of knowledge we’re expecting to get here. There definitely is plenty of varied information available on the economic impacts of, for instance, “shadow economies” or informal labor and commercial exchanges. Thousands of economists (e.g., at the IMF) earn their bread and butter quantitatively estimating the very sort of thing that you ignorantly assert “no one can know”.
And, of course, if our hypothetical entrepreneurs with their part-time accountants are running legit enterprises with tax status and all, it becomes much easier to estimate their economic impact. There’s plenty of research on the subject of specific and general economic consequences of US microbusiness.
So no, I’m not buying your and Starving Artist’s defeatist pessimistic negative lazy unmotivated irresponsible excuses about being incapable of attaining anything but total ignorance about the economic impacts of the entrepreneurship you’re promoting, if it were to be implemented on a larger scale than just the occasional random striving individual.
You may not have the intelligence or initiative to get off your booty and develop some quantitative estimates about the economic impacts of microbusiness entrepreneurship, but that doesn’t entitle you to say that it can’t be done at all.*
[QUOTE=octopus]
Your ideological cohorts want to raise minimum wage to $15/hr. What impact will that have on all the poor?
[/QUOTE]
Wow, you thought that would be a stumper?
This is one of the most heavily researched domestic-economy questions of all time. (Of course, as with all these other topics, there’s no hope of getting absolute certainty or precision or universal agreement, but there’s definitely a lot more quantitative information available than your go-to response of “We don’t know anything about that. Nobody can know anything about that. And you know it. Derrrrrrrrp.”) A sizable chunk of such information is available in this summary of research and arguments concerning minimum wage increases.
- Cue octopus and Starving Artist pouting in unison “Well fine, then you go and find out quantitative estimates of entrepreneurship impact for us if you’re so smart!” Yeah, sorry boys, but it’s your policy proposal, so it’s up to you to back it up with data-based rationales if you expect anybody else to be convinced by it.