intdots.gif (546 bytes)
white1.GIF (834 bytes)

Logic Goes Extinct As Press Overplays Overpeck

Federal climatologist Jonathan Overpeck is in danger of replacing NASA’s James Hansen as the 1998 Apocalyst Poster Child. Overpeck recently released a spate of papers and conference presentations about past and future climate.

In the Bulletin of the American Meteorological Society, for example, he argued that, with or without human-induced global warming, we’re headed for some tremendous droughts next century. And, of course, the greenhouse effect will make things even worse!

And in an earlier presentation at the December meeting of the American Geophysical Union, Overpeck asserted the so-called Medieval Warm Period was local, not global. We’ll concentrate on that one here.

His bombshell concept is that the Medieval warming was so substantial that it allowed the Vikings to sail westward without freezing to death, colonizing Greenland and North America, but it was not created by a general planetary warming. This theory implies that the Little Ice Age, the cooling that later decolonized that area, was similarly nonglobal; otherwise the Warm Period would have shown up as, well, global warming, compared with succeeding centuries.

Overpeck’s speech prompted handsprings of joy from our greener friends. Now, instead of saying that the 1990s (and, in particular, 1998) are the warmest in 600 years (which goes back to the beginning of the putative Warm Period), they can say they’re the warmest in 1,200 years. "Obviously," they can remark, "the Warm Terror is here and we need to raise taxes pronto to stop the burning of fossil fuels."

Others might say, "Sure am glad I haven’t spent a lick on heating oil and it’s almost Christmas. Think I’ll go and buy some stuff for the missus."

Still others, somewhat more penurious and even-headed, realize that Overpeck has created the apocalyst’s biggest nightmare. If he’s right, then regional climate naturally varies tremendously, whether or not the globe warms. Climate changes so dramatic that they promoted Viking exploration are simply the way of things. And ditto for their flipside—large regional coolings such as the Little Ice Age, an event that sent the Rhone Glacier in the Alps some 5,000 feet farther downslope than it is today.

Poignant testimony to the social consequences of this regional swing can be found in Kalaallit Nunaat (That’s politically correctese for Greenland these days), where masonry churches, once built in pastures, are now encased in ice. While K.N’s climate clearly changed in ways that were tremendously important to society in Viking times, this apparently had nothing to do with global warming or cooling.

Instead, Overpeck says, these changes occurred as pure internal oscillations of the climate system, with no external global change.

If we accept the notion that large regional changes in climate are independent of the global temperature, what does it really mean? Forecast climate changes of the magnitude that is driving the current hysteria will occur whether or not the planet warms. Further, those who would seek to impose costs on society now must demonstrate that warming the planet will make these changes more, not less, likely.

We recently explored this notion in the refereed literature. Relying upon data (and explicitly ignoring computer models of climate because of their patent unreality), we found that temperature variability between seasons and between years has significantly declined in the second half of this century. And there have been a few warm years in that period, too.

So, when we looked at the variability as a function of the planet’s annual temperature, we found that the cool years were more variable and the warmer ones less so, as our figure shows. Conclusion? Warming the planet decreases variability on a year-to-year scale. Cooling the planet makes things more variable.

Figure 1. Our recent look into the relationship between global temperatures and temperature variability showed that higher temperatures are associated with less temperature variability and lower temperatures.

We think that’s pretty good evidence that what human beings are doing to the climate makes things more predictable and equable than before.

Want more evidence? When the atmosphere’s carbon dioxide concentration was at its highest level since animals first appeared, the largest animals in history roamed the earth: dinosaurs. These beasts required a tremendous amount of vegetation to reach their enormous size. Carnivores such as T. rex were in turn supported by the massive herbivores. How many tons of vegetation were ultimately required to feed him, considering it had to pass through huge lunks like Apatosaurus? (That’s Brontosaurus to you intellectual dinosaurs.) The earth had to have been greened beyond recognition.

What’s more, when the dinos were around, the climate was so stable that they were cold-blooded! They’d probably still be here today if they hadn’t gone extinct when the earth got clobbered by a small asteroid. Said asteroid raised a huge cloud of dust and killed them with global cooling, which made the climate more variable, resulting in an undependable food supply.

We think our greener friends might go extinct too if they tout Overpeck’s findings as good news for their side.


Overpeck, J.T., 1998, How unprecedented is recent Arctic warming: A look back to the medieval Warm Period. Presented to the Fall Meeting of the American Geophysical Union, San Francisco, Calif.

Michaels, P.J., et al., 1998, Analysis of trends in the variability of daily and monthly historical temperature measurements. Climate Research, 10, 27–33.



The long-awaited drop in global temperatures following the breakdown of last year’s massive El Niņo has finally appeared in the observations.

The global temperature departures, as measured by satellites, show a large decline from October to November—more than a quarter of a degree Celsius. We had previously hypothesized (WCR, Vol. 4, No. 3) that this decline would occur as the Northern Hemisphere transitioned from a summerlike regime to a winterlike one.

It looks as if this switch took place last month (see Earth Track Focus) for more detail.

That 1998’s extremely warm temperatures were largely confined to one calendar year makes the annual record high temperature 1998 has established quite a difficult one to break.

If we were of a betting sort (and there are some nasty rumors going around that we are), we would be willing to wager that the 10-year period beginning in January 1998 and extending through December 2007 will show a statistically significant downward trend in the monthly satellite record of global temperatures.

Surely such a wager should sound interesting to those who think the planetary temperature will increase several tenths of a degree during that period.

No reasonable offers refused...