A half billion years ago–it is 450M or 650M, not sure–the earth was very cold yet had 10x CO2.
Never heardof that, but 0.5 billion years ago the Sun indeed could have been in a different configuration, and besides that is probably near the time of evolution of eukaryiotic cells.
More recently there was the Paleocene-Eocene thermal maximum which had lots of extinction, with CO2 levels of 2000-3000 ppm, and crocodiles in the arctic. Permian-Triassic mass extinction may also have been caused by global warming from immense volcanism and release of oceanic methane hydrates.
Anthropogenic CO2 being the primary reason for 20th century warming is still an unproven theory that was borne out of 1. the need to assign blame to man for global climate change, and 2. noticing correlations in the geological record.
So if #2, noticing correlations in the geological record is unreliable, then your first comment is also irrelevant.
But it is asserting a lie, that the primary impetus came from ‘correlations in the geological record’. This is flatly untrue, since the idea was first advanced in the 19th century before any of the geological record was known.
Screw the geological record, and just go by presently observed physical phenomena:
1) GHG re-radiate infrared. This is observed fact.
2) The amount reradiated is increasing. This is observed fact.
3) The GHG concetration is incresasing because of humans. This is observed fact. The numbers of #1,2,3 all go together.
4) Laws of electromagnetism and thermodynamics say that when there’s more atmospheric emissivity the temperature will go up.
These four essentials have been there since the beginning and have never been invalidated, and won’t be. Anthropogenic global warming is based on physics, not just correlations. If somebody first saw the correlations, then the next task would be to search for the mechanism. If there wasn’t one then the correlation would be suspect. Since there is a mechanism, and the correlation is very good, it gives the obvious conclusion.
