Ice and History

摘要

If you paused at the table of contents, you noticed that there is a lot about ice in this issue. Ice is important not only because we are losing it but also because it is an archive that has told us much about past climates. But the climate-change debate has focused perhaps too much on the past few hundred years. That baseline has told us much about what has been happening to global temperature lately, but it may not be the best baseline to use in exploring our future. For that, the relationship between greenhouse gas levels and temperature, evident in data from ice cores, illuminates climates in the geological past and may be a more useful guide to the future. Fifty million years ago, CO_2 levels may have topped 1000 parts per million by volume (ppmv) and sea levels were about 50 meters higher than those today. CO_2 levels gradually decreased as marine organisms fixed carbon through photosynthesis and then buried it by sinking into the ocean basins.