Looks like old times

Published February 1, 2000

The computer models that started all the fuss about global warming predicted the entire bottom 40,000 feet of the atmosphere would be warming around 0.7°F (0.4°C) per decade by now. That hasn’t happened.

After allowing for the fact that the sun’s output fluctuates a bit, the most warming we can attribute to human beings is around 0.2°F (0.1°C), and this change is largely confined to the bottom 4,000 feet of that layer in the last quarter of this century.

When pressed, environmentalists will usually admit these facts. But, they argue, the changes still occur so fast that ecosystems—plants and animals—will be unable to adjust. After all, they point out, trees can’t move.

This argumentative redoubt was blown to bits by Julian Sachs and Scott Lehman in a little-noticed paper in the October 22 issue of Science magazine.

For years, climatologists have known that temperatures fluctuate widely in the high latitudes, particularly around Greenland, Siberia, and Northern Canada. Air bubbles trapped in the Greenland ice reveal swings in mean temperature in excess of 9°F (5°C) in a given century.

But in the more temperate and tropical latitudes, where most things live, such fluctuations have been considered rare. For this reason, predictions of 5°F to 7°F (3°C to 4°C) of warming (resulting from human-induced climate change) are alarming when made for regions far away from the poles.

But what if these types of temperature changes were common and occurred naturally over much of the globe? What would that say about the importance of “global warming” on the grander scale of things?

Looking at the annual layers of chemicals trapped in sediments near Bermuda, Sachs and Lehman determined that sea-surface temperatures in the region “changed repeatedly from 2°C to 5°C [4°F to 9°F], [changing simultaneously] with high-latitude temperatures that were previously inferred from Greenland ice cores.”

Translation: Temperatures in tropical oceans (Bermuda is on the warm, or tropical, side of the Gulf Stream) change as dramatically as those in Greenland, and at the same time.

The authors concentrate on two rapid cooling incidents in their record, which appeared to occur over about 250 years. But they neglected to emphasize two phenomenally rapid warmings—of 9°F (5°C)—that also show up in what appears to be less than 100 years. Their report, effectively demolish the “rapid change” argument that environmentalists fall back upon when confronted with the failure of recent predictions. In fact, the more logical argument, Sachs and Lehman’s paper indicates, is that the biota adapt to these kinds of fluctuations.

Their research, which covers only the period from 30,000 to 60,000 years ago, contains at least eight rapid changes. If their results are characteristic of the Earth’s climate during a time when ice age cycles were prevalent (which includes the last 2.5 million years or so), then it is likely that 800 of these quick-change events have occurred during that period.

For comparative purposes, think of these rapid and temporary climate fluctuations as akin to extra-long “El Niños.” People make a big mistake when they blame all-things-terrible on natural, repetitive phenomena. We experience an El Niño event about one-sixth of the time. If the Earth’s biota (and, for that matter, the Earth’s people) had not adapted to this cycle, we all would have gone extinct a long time ago.

On the contrary, plant and animal life adapt—whether to something as common as El Niño or to the rapid, hemispheric (or maybe even global) temperature swings Sachs and Lehman found. That’s the nature of things economic and ecologic: Adapt and prosper, or fail and go extinct!

According to Nature magazine, University of Virginia environmental sciences professor Patrick J. Michaels is probably the nation’s most popular lecturer on the subject of climate change. Michaels is the author of Sound and Fury: The Science and Politics of Global Warming.


Sachs, J.P., and S.J. Lehman, 1999, Subtropical North Atlantic temperatures 60,000 to 30,000 years ago, Science, 286, 756–759.