Climatologist's Toolbox





 






Photo by Jeff Miller.
© Office of News and Public Affairs, University of Wisconsin-Madison.
















 





















Photo courtesy of Jim Hurley.
Research Bureau, Wisconsin Department of Natural Resources.

What's this cinder doing in my core sample?
Even microscopic bits of charcoal have a climate tale to tell. Exploring the layered sediment from a series of lakes in Wisconsin and Massachusetts, paleoecologist Marjorie Winkler reconstructed a 14,000 year history of wildfire. That history provides important insights into the interplay of climate, fire and the plants that dominated the landscape.

core slice

"What the record tells us is that fire history changes with climate. It's a climate-dependent phenomenon that essentially determines the vegetative makeup of the landscape. Plants either adapted to these fires or were eradicated by them," she says.

Winkler's history of fire shows that landscapes of the Midwestern and Eastern United States exhibited great variation, evolving from the spruce-dominated tundra of the immediate post-glacial period 14,000 years ago to the closed forests, pine barrens and prairies of recent prehistory.

In the interval, the record shows times of intense biotic change that coincide with cyclic changes in the orbit of the Earth and the tilt and wobble of its axis. "The period of most intense change was between 10,500 and 9,000 years ago when hardwood species such as elm, beech, chestnut, hickory and maple emerged, and conifer species such as spruce, jack pine and fir disappeared," says Winkler.

"This time of instability was when the seasons were most influenced by changes in the orbit of the Earth. It suggests that orbital changes may have had a great influence on biotic response."

Warming trend
At this time of changing climate, the Northern Hemisphere of the Earth was subject to increased solar radiation because its perihelion (defined) was in July rather than in January as it is now. The tilt of the Earth on its axis also favored increased solar radiation, and helped create seasonal extremes and prime conditions for fire in some parts of the world, increased monsoons (defined) in other regions, and sweeping changes in the biological makeup of the landscape.

The kinds of core samples obtained by Winkler and others not only help us look back in time, but also serve as critical points of reference for the scientists who use computer models to study climate. Many of the big supercomputer-driven models attempt to forecast climate. But some scientists run the models backwards in time. By doing so, they can reconcile their models with actual physical evidence like the kind Winkler draws from the mud of lakes and bogs.

It's a bit of a reality check, says Winkler. It helps work the kinks out of the same models that will be used to try and forecast future climates.

Too bad at least one ancient civilization didn't have access to a sediment record like this. They might have saved themselves the trouble of cultural collapse.

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