The present level of CO2 is already at a point where we are headed for major problems. And that is without the continueing positive feedbacks that we are seeing in the release of CO2 and CH4 sequestered in the permafrost and ocean clathrates. Climate Change: The Next Generation: BBC: Current 400 ppm CO2 levels equivalent to 25-40 m higher sea levels during the Miocene; should go back to 180-280 ppm A new historical record of carbon dioxide levels suggests current political targets on climate may be "playing with fire," scientists say. 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 25-40 m (80-130 ft.) higher than today. Scientists write in the journal Science that this extends knowledge of the link between CO2 and climate back in time. The last 800,000 years have been mapped relatively well from ice cores drilled in Antarctica, where historical temperatures and atmospheric content have left a series of chemical clues in the layers of ice. But looking back further has been more problematic; and the new record contains much more precise estimates of historical records than have been available before for the 20-million-year timeframe. Sustained levels 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.