More settled science: 400,000 years ago, the Earth was quite a bit warmer than now. Or about the same. Or cooler.

During MIS11 interglacial sea levels were 6-13 m higher, Nature study shows | Bits of Science

They focussed on an interglacial with a particularly charming name, Marine Isotopic Stage 11, which reached its climatic optimum some 400,000 years ago.

Previous research had suggested that during MIS 11 the world’s oceans could have been 20 meters higher than they are today.

...We are however left with a bit of uncertainty here. In the 90s paleoclimatologists thought that MIS 11 must have been quite a bit warmer than the Holocene. Now however some think the climate was very similar to our preindustrial climate (and so were CO2 levels) – and some even think MIS 11 could have been cooler.

It really makes you wonder why, 10,000 years into the Holocene, we still have that large ice sheet on Greenland. More and more studies seem to suggest it is actually an ice age relict – and perhaps indeed one that has managed all these years to keep itself in place and intact because of its albedo and its high ice surface height – factors, like atmospheric temperature, that are clearly no constants…