Wha? Atmospheric CO2 has been rising since the start of the Industrial Revolution in the early 1800s. Besides CO2 industry also spits out a lot of other air pol

Wha? Atmospheric CO2 has been rising since the start of the Industrial Revolution in the early 1800s. Besides CO2 industry also spits out a lot of other air pollutants that take a while to break down in the atmosphere. I'd posit that we started polluting faster than natural breakdown rates in the mid-1800s. So the radius that would be able to detect industrial civilization on Earth would be about 170ly, not 100ly. There's also a few hundred[0] G-type stars within 100ly of Earth, if we include F and K types we've got thousands of stars within 100ly. We're just on the cusp of observatories that will be able to get spectra from terrestrial planets in close (<5 AU) orbits around their host stars. So a civilization within 200ly of us just slightly more advanced would be able to not just detect Earth, life signs on it, but also have at least a guess there's a technological civilization here.