In New York, about 60-65% of your electricity is emmission-free, with most of the rest being gas. In Ohio or Kentucky, it's all coal and gas. You're probably emitting more in Kentucky with a laptop than you are in NY with a workstation.

The whole argument is tedious and obnoxious anyway, as the marginal negative impact of squeezing a couple of years out of an older device is overstated and minimal -- you'd be better off assuaging your guilt by taking a 5m shower.