My brother has kindly forwarded the following video by an Australia-based British scientist whose former field was geology. It shows that when you combine atmospheric CO2 levels with the variable luminosity of the sun, you do indeed get a good fit with the graph of the Earth's temperature over the last 500 million years.
Though water vapour can also contribute to the greenhouse effect, its role is limited because beyond a certain limit, the excess falls to earth as precipitation. However, a warmer atmosphere can hold more vapour.
It seems that we are in a "fool's paradise" period (my label) because although atmospheric CO2 has risen significantly, much of the additional heat stored in the system has been absorbed by the oceans, and at the same time there has been a temporary weakening of the sun's radiation. When the sun's energy emission resumes its long-term upward trend, and if the ocean warming crosses some point where new things happen (e.g. the release of deep-sea dissolved methane?) we may get climate change with a vengeance.
Yes, the Earth has been much warmer in the distant past - when humans did not exist. Life will probably continue, but maybe not on terms that favour our species and civilisations.
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