As techniques improve, we are finding more ways to study the past climate history of our planet in detail. The following site has far more information than just what is in the post. Science: CO2 levels haven’t been this high for 15 million years, when it was 5Â° to 10Â°F warmer and seas were 75 to 120 feet higher — “We have shown that this dramatic rise in sea level is associated with an increase in CO2 levels Tripati, before joining UCLAs faculty, was part of a research team at Englands University of Cambridge that developed a new technique to assess carbon dioxide levels in the much more distant past by studying the ratio of the chemical element boron to calcium in the shells of ancient single-celled marine algae. Tripati has now used this method to determine the amount of carbon dioxide in Earths atmosphere as far back as 20 million years ago. We are able, for the first time, to accurately reproduce the ice-core record for the last 800,000 years the record of atmospheric C02 based on measurements of carbon dioxide in gas bubbles in ice, Tripati said. This suggests that the technique we are using is valid. We then applied this technique to study the history of carbon dioxide from 800,000 years ago to 20 million years ago, she said. We report evidence for a very close coupling between carbon dioxide levels and climate. When there is evidence for the growth of a large ice sheet on Antarctica or on Greenland or the growth of sea ice in the Arctic Ocean, we see evidence for a dramatic change in carbon dioxide levels over the last 20 million years. A slightly shocking finding, Tripati said, is that the only time in the last 20 million years that we find evidence for carbon dioxide levels similar to the modern level of 387 parts per million was 15 to 20 million years ago, when the planet was dramatically different. Levels of carbon dioxide have varied only between 180 and 300 parts per million over the last 800,000 years until recent decades, said Tripati, who is also a member of UCLAs Institute of Geophysics and Planetary Physics. It has been known that modern-day levels of carbon dioxide are unprecedented over the last 800,000 years, but the finding that modern levels have not been reached in the last 15 million years is new.