In trying to develop a mature perspective concerning the likely extremes of global climate change, I've been googling on data about the various geologic eras and the ice ages that occurred therein. Some of the more severe glaciations (e.g., snowball Earth) occurred with atmospheric concentrations of CO2 at the level of several thousands of parts per million during the Proterozoic era as opposed to less than 400 parts per milion currently. Although, in the articles that I read, nothing was said about what I suspect was a much larger amount of internal heat escaping through the Earth's surface, although the likelyhood of volcanic action disturbing the ice cover was mentioned now and then as possible triggers initiating a regression to the mean temperature. The most severe global temperature I saw was "estimated" to have been ~-50 celsius.
I accept as self evident that some global warming is occurring over the last few centuries, but I'm less sure about its cause being the piddling amount, including the increases over the last two centuries of CO2 in the Earth's atmosphere. I'm still mired in disbelief concerning the eccentricity component of the Milankovitch Cycles; I fail to see what changes the eccentricity on a regular basis, nor how it could be restored to very near zero. Consequently, my confidence that we do not have adequate climate change prediction models remains strong.
Learning about the severity of the Proterozoic climate swings during relatively high levels of CO2 concentration has increased my befuddlement. Can anyone help sort this out? Is there significance to the fact that the atmosphere of Mars contains more kg of CO2 than does that of Earth?