Global warming v. Solar warming

At the risk of waking up the trolls - Sorry!

There has been a lot of talk lately about the rise in earth temperature
being caused by a secular increase in solar output rather than the
greenhouse effect of various pollutants.

Surely there is an easy way of getting some objective evidence on this?
Mars has been closely observed for many years. If this is a solar
effect, the polar caps, as seen at different apparitions, but at
comparable distances from the sun, should show a variation over time.
If not, then the greenhouse gasses are to blame.

But that might settle the argument, so perhaps it's a bad idea.

Roger