'Scary' new historical CO2 data and high sea levels

From the above linked BBC article: "Researchers used ocean sediments to plot CO2 levels back 20 million years.  Levels similar to those now commonly regarded as adequate to tackle climate change (read 450 ppm) were associated with sea levels 25-40m (80-130 ft) higher than today."

The science is based on "the ratios of boron and calcium in the shells of tiny marine organisms called foraminifera. The ratio indicates the pH of sea water at the time the organisms grew, which in turn allows scientists to calculate the carbon dioxide content of the atmosphere. The shell fragments came from cores drilled from the floor of the Pacific Ocean."

A second linked  article in Reuters uses a comparable approach by different scientists to arrive at similar conclusions. In this study they went back further in time to when CO2 levels were 750 ppm. Both articles were based on results published in the journal Nature.