Climate Change in Historical Documents

The AP reported yesterday about a new source of evidence on global warming: Ancient manuscripts.

EINSIEDELN, Switzerland - A librarian at this 10th century monastery leads a visitor beneath the vaulted ceilings of the archive past the skulls of two former abbots. He pushes aside medieval ledgers of indulgences and absolutions, pulls out one of 13 bound diaries inscribed from 1671 to 1704 and starts to read about the weather.

"Jan. 11 was so frightfully cold that all of the communion wine froze," says an entry from 1684 by Brother Josef Dietrich, governor and "weatherman" of the once-powerful Einsiedeln Monastery. "Since I've been an ordained priest, the sacrament has never frozen in the chalice."

"But on Jan. 13 it got even worse and one could say it has never been so cold in human memory," he adds.

Diaries of day-to-day weather details from the age before 19th-century standardized thermometers are proving of great value to scientists who study today's climate. Historical accounts were once largely ignored, as they were thought to be fraught with inaccuracy or were simply inaccessible or illegible. But the booming interest in climate change has transformed the study of ancient weather records from what was once a "wallflower science," says Christian Pfister, a climate historian at the University of Bern.

The accounts dispel any lingering doubts that the Earth is heating up more dramatically than ever before, he says. Last winter — when spring blossoms popped up all over the Austrian Alps, Geneva's official chestnut tree sprouted leaves and flowers, and Swedes were still picking mushrooms well into December — was Europe's warmest in 500 years, Pfister says. It came after the hottest autumn in a millennium and was followed by one of the balmiest Aprils on record.

No, these accounts do not dispel any lingering doubts about dramatic heating. These accounts just feed into the hype.

I'm not a scientist. The sum total of science classes I've taken at the college level is two: General Biology, and Anatomy & Physiology. But I've learned enough in the time I've been on this Earth (heating or not) to know that you form a hypothesis, and then you seek as much information as you can on the topic, until you either support it, shoot it down, or determine you need more information.

But when the topic is global warming (excuse me, "climate change"), you're supposed to form your hypothesis, ignore information that might refute it, and tell everyone else to shut up about it.

Here's what I mean:

The diaries of Brother Josef Dietrich were written between 1671 and 1704. He said it was colder than human memory. But these days, it's not as cold in his time. Therefore, Pfister concludes that the Earth is heating dramatically.

But he fails to look at a couple key pieces of information that should influence his conclusion. The first is the Little Ice Age, which occurred between the 16th and the mid-19th centuries. Its very name should tell you that it was unusually cold. Colder than normal. Cold enough that they gave it its own special name. Cold enough that any warming since the mid-1800s shouldn't be judged only against its temperatures. Except, Pfister seems to be doing that very thing. Not very scientific...

The second key piece of information is the Medieval Warm Period, which occurred between the 10th and the 14th centuries. Its name tells you that it was unusually warm. Warmer than normal. Warm enough that they gave it its own special name. Warm enough that any heating of the Earth should be compared against its benchmark before disaster is declared for life as we know it. But Pfister seems to be ignoring it because he doesn't have any ancient manuscripts from that time period that detail the weather. Not very scientific...

What would be scientific would be to look at the whole record. If they're going to use the Little Ice Age in their calculations of Earth's "normal" temperature, they need to also use the Medieval Warm Period in those calculations. Normal should either include both extremes or neither. Including just one extreme only serves to distort the results of the past, which distorts the projections for the future.

Now before you come after me about the criticism mentioned in the Wikipedia article on the Medieval Warm Period, that it does not appear to have been global, I'd like to point out something: Brother Josef Dietrich's weather reports weren't global either. He was in Switzerland, which is in Europe, which experienced both the Medieval Warm Period and the Little Ice Age. So if Pfister and other global warming scientists want to use Brother Dietrich's records, they had better do it scientifically.