'Scary' climate message from past

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 were associated with sea levels 25-40m (80-130 ft) higher than today.
The new research was able to look back to the Miocene period, which began a little over 20 million years ago.

At the start of the period, carbon dioxide concentrations in the atmosphere stood at about 400 parts per million (ppm) before beginning to decline about 14 million years ago - a trend that eventually led to formation of the Antarctic icecap and perennial sea ice cover in the Arctic.

If anyone still doubts the link between CO2 and climate, they should read this paper
Jonathan Overpeck
University of Arizona

The high concentrations were probably sustained by prolonged volcanic activity in what is now the Columbia River basin of North America, where rock formations called flood basalts relate a history of molten rock flowing routinely onto the planet's surface.

In the intervening millennia, CO2 concentrations have been much lower; in the last few million years they cycled between 180ppm and 280ppm in rhythm with the sequence of ice ages and warmer interglacial periods.

Now, humanity's emissions of greenhouse gases are pushing towards the 400ppm range, which will very likely be reached within a decade.
"At CO2 levels that are sustained at or near modern day values, you don't need to have a major change in CO2 levels to get major changes in ice sheets," she told BBC News.

The elevated CO2 and sea levels were associated with temperatures about 3-6C (5-11F) higher than today.
full article