Eugene S. Takle
© 2005
Kerr (2005) overviews an article by Wara et al. (2005) that reports proxy data from a period 3.0 to 4.5 million years ago, the last time the Earth was as warm as it is today. Wara et al. (2005) find that atmospheric circulation in the tropics was quite different under those conditions of the past. With global mean temperatures projected to rise about 1.5 to 5 degrees C over the next hundred years we could see conditions 3 degrees above today's mean temperature and therefore might resemble those of the Pliocene, during which transport of heat from tropics to poles was quite different from today. The earlier period had more of a permanent El Niño rather than the alternating El Niño/La Niña of today.
References
Kerr, R.A., 2005: El Niño or La Niña? The past hints at the future.
Science, 309, 687.
Wara, M.W., A.C. Ravelo, and M.L. Delany, 2005: Permanent El Niño-like
conditions during the Pliocene warm period. Science, 309, 758-761.