What Heated Up the Eocene?

摘要

Talk about your global warming. Fifty-five million years ago, carbon dioxide gushed into the atmosphere over as little as a millennium, acidifying the ocean and scorching the world of the Eocene epoch with a 5°C greenhouse warming. At least two more progressively weaker "hyperthermals" would strike during the next few million years. So where did all that carbon dioxide come from? The possibilities are expanding, from the sea floor to an ice-free Antarctica. In one presentation, earth systems modeler Andrew Ridgwell of the University of Bristol in the United Kingdom and his colleagues suggested an ocean source. Earth is always wobbling on its axis like a spinning top, and its orbit about the sun is rhythmically stretching into an ellipse and relaxing to more of a circle. By changing how much sunlight falls at different latitudes in different seasons, these orbital variations can make for exceptionally warm summers with extra-cold winters, for example.