The great exhale: CO2 and the extinction of species
Atmospheric carbon dioxide today registers 390 parts per million, and counting. Even in the most optimistic global scenarios, our fossil-fuel-burning ways will result within the next 100 years in a full doubling of the preindustrial amount of atmospheric carbon dioxide—up to 560 parts per million—and beyond.
At the United Nations Climate Change Conference in Bonn this month, nations will try again to come to grips with the enhanced greenhouse effect spurred by this rise in the Molecule of the Millennium. But let’s set aside for a moment the future implications of the CO2 shift and go back 40 million years to the last time that an atmospheric shift of this magnitude took place. A look back provides a startling perspective on how different the environments of the earth have been—and how different they may become.
As far as scientists can tell through analyzing soil and sediment, the last time the planet’s atmospheric CO2 hovered around 560 ppm was 40 to 50 million years ago. What happened next was that carbon dioxide levels were cut in half, falling from over 560 to 280 ppm. This swing took a very long time—25 million years. (Compare that to the pace of change we are on now, which forecasts CO2 amounts doubling in 250 years.)
