400 ppm CO2 is still quite low, if compared to the geologic record.
I think it is important to distinguish between short term (say, 1000 years or less) cycles, medium term cycles (such as the glacial and interglacial cycles in our present Ice Age), and long term events (generally many millions of years long) such as our current Ice Age (the Quaternary Ice Age, if you want to use Arctic glaciation as the starting point of the present Ice Age, or, more correctly, IMO, the Late Cenozoic Ice Age, using consistent Antarctic glaciation as the signal that the present in-general-cooling trend was well established).
I would note that designating an event or period “long term” does NOT mean it might not have a relatively rapid onset or conclusion, and, as with our present Ice Age, the variations within it can be very large.
It does appear “Snowball Earth”, IF it occurred, was likely ended by a vast release or accumulation of greenhouse gases, but the concentrations are hundreds of times higher than modern values. Many other factors were different too. Comparison of the end of “Snowball Earth” to modern climate variations is not even relevant.
OTOH, ocean levels are not entirely irrelevant. See my next post. The temperature spike in the interglacial immediately prior to the present interglacial is fairly impressive. There is another at approx. 330k years back. Although our present interglacial, so far, looks more like the one 400k years ago, who is to say we could not still get a spike of at least 6 deg. C even without any “input” from humans at all? If anything, what we should concentrate on is creating the most wealthy, powerful society possible, to best deal with whatever Mo’ Nature throws at us...
“If anything, what we should concentrate on is creating the most wealthy, powerful society possible, to best deal with whatever Mo’ Nature throws at us...”
I agree with you. Regardless if one thinks climate change is a hoax or believes it’s real, a person, doesn’t have to be wealthy, ought to take steps to prepare for whatever may be thrown at him or her. And I think it’s going to have to be individuals as there is no political will at the national level to do so. As a nation, we are a people who don’t do shit until the shit gets real and cannot be ignored.