> My impression is that almost no one denies the warming itself, just the link to greenhouse gasses. That link is unfortunately much harder to prove than rising temperatures by itself.

The link to greenhouse gases is not hard to prove. We've got satellites that can measure global radiation inflow and outflow and see what the difference is. We can also measure this at various levels within the atmosphere, and at the surface of the land and oceans. We can see where outgoing radiation is getting caught and we can see what frequency bands of outgoing radiation is getting caught.

We know the frequency bands that get reflected, absorbed, or pass through for all the gases in the atmosphere and can see that the gases causing the problem are the greenhouse gases.

We can also see that the increase in greenhouse gases is mostly from burning fossil fuels. We can see this by looking at the isotope ratios in the C in greenhouse gases.

Cosmic ray bombardment in the upper atmosphere produces carbon 14, which is radioactive with a half live of 5730 years. It disperses throughout the atmosphere and becomes part of anything that regularly incorporates atmospheric carbon or exchanges its carbon with atmospheric carbon, including all living things.

Everything humans do in significant amounts that puts greenhouse gases in the atmosphere other than burning fossil fuels has carbon with about the same isotope ratio as that of the carbon in living things. Even when we burn a dead forest to clear it out the isotope ratio is close to that of living things, because of that 5730 year half life for carbon 14.

It is only when we burn fossil fuels that we put carbon into the atmosphere with almost no carbon 14. They came from living things but have been dead long enough for hundreds of half lives to pass.

The isotope ratios in the excess greenhouse gases show that it is mostly carbon 14 free. There are natural processes that can dump carbon 14 free carbon into the atmosphere such as volcanoes and other geological processes. However, (1) the increases in carbon 14 free greenhouse gases matches very closely with the amount of carbon we've been emitting from fossil fuels, and (2) and monitoring of volcanoes and other natural sources doesn't find nearly enough to account for more than a small amount of the increase.