Those who deny the reality of climate change like to point out that dramatic weather events have occurred in the past; they argue that we may be in the midst of a cycle we don't understand, rather than a trend caused by human activity.

New research from the U.S. National Science Foundation looks at a previous "cycle" -- one that occurred 55 million years ago and that resulted in warming-induced changes in sea circulation [1] that appear similar to what are currently occurring in the northern hemisphere.

For those who would take comfort in the cyclical argument, consider that on the earlier occasion, the "cycle" took 20,000 years to reverse itself -- a little beyond our current planning horizon.