If atmospheric gases separated out due to gravity we would all be in a lot of trouble as we would be breathing only the heavy gases like the CFCs, CO2 etc.

Wind keeps them all pretty well mixed luckily for us.

The reason ozone depletion has fallen off the political radar is that in the mid 80s the international community got together and thrashed out the Montreal Protocol which resulted in the gradual phasing out of chlorinated fluorocarbons as refrigerants and aerosol propellants, among other uses.

The chlorine in these gases was the main problem as it reacts with ozone (O3) in the upper atmosphere converting it back to diatomic oxygen (O2).

Ozone absorbs UV radiation, O2 doesn’t.

One of the big champions of their phases out was that bastion of pinko ideology Du Pont who had developed their replacement, HFCs or Hydroflruorocarbons.

Far from being an example of a discredited alarmist theory it is more an example of how international co-operation can achieve a positive outcome.

The ozone hole still exists but, with the replacement of CFCs, over time it will hopefully repair itself.

As far as global warming goes, the understanding that atmospheric gases warm the earth has been around for over 150 years.

Simplistically they absorb electromagnetic radiation in the higher energy spectrum, visible light, UV and emit infrared or heat.

They also act as a blanket trapping the radiated heat leaving the planet surface.

This is demonstrated by cloudy nights being warmer than clear nights.

Water vapour (also heavier than air) is the most important greenhouse gas followed by C02, then other less common gases.

This is pretty much universally accepted, no controversy there.

Atmospheric scientists have postulated the idea that increasing atmospheric CO2 concentrations from 270 ppm pre industry to almost 400ppm today would lead to a warmer earth for a number of decades.