Here's the CENOGRID data, the Cenozoic global reference benthic foramanifer carbon and oxygen isotope dataset. It's a decades long scientific effort to produce an astronomically tuned high-definition stratigraphic reference of global climate evolution over the last 66 million years. Currently we are in an interglacial period within an ice age. Atmospheric CO2 was 800-1000ppm for most of the last 66 million years, and sometimes 2000ppm, and global temperature was much warmer than today. All of today's mammalian life evolved during that period, and every living organism alive today has an ancestor that lived through that time. Sea level has risen 120 meters, almost 400 feet, since the last ice age ended 11,500 years ago, and it was 35 meters, about 120ft, higher than today during the last interglacial period 125,000 years ago. Hundreds of million of years of carbon capture in the form of coal, oil, and limestone has reduced atmospheric CO2 to the point that it has plunged us into an ice age. If CO2 gets down to about 150ppm, plants can no longer photosynthesize and they die, along with all the life on earth that depends on them. "Why the fascination with ancient climate when humans have only been around for a few hundred thousand years?" Well, why the fascination with only tiny geological time scales and only the most recent climate? Answer that one? So if some kooky environmental Doomsday cultist with no climate science qualifications tells you "The end is near, you will perish in flame if you don't obey my climate warnings", you can tell them "Follow the science" and show them this graph, because they'd obviously rather have us living on a barren lifeless snowball. So you see, when we burn fossil fuels, we're actually saving the planet.
