Ancient records help test climate change

CBS News, via AP:…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.

"In the last year there was a series of extremely exceptional weather," he says. "The probability of this is very low." The records also provide a context for judging shifts in the weather. Brother Konrad Hinder, the current weatherman at Einsiedeln and an avid reader of Dietrich's diaries, says his predecessor's precise accounts of everything from yellow fog to avalanches provide historical context.

….Most historians and scientists delving deep into archives seek accounts of disasters and extreme weather events. But the records can also be used to obtain a more precise temperature range for most months and years that goes beyond such general indicators as tree rings, corals, ice cores or glaciers.

…Pfister has found that from 1900 to 1990, there was an average of five months of extreme warmth per decade. In the 1990s, that number jumped to an unprecedented 22 months. The same decade also had no months of extreme cold, in contrast to the half-millennium before.

Even in the last major global warming period from 900 to 1300, severe winters were only "somewhat less frequent and less extreme," Pfister says. Over the past century, temperatures have gone up an average of 1.3 degrees Fahrenheit, which is often attributed to the accumulation of greenhouse gases, primarily carbon dioxide, in the atmosphere…