From sediment samples drawn out of New England earth, Professor of Geology Jack Ridge is trying to reconstruct the climate here as it was tens of thousands of years ago.
As many modern geologists and meteorologists puzzle over the intricacies of the global warming that is taking place today, Ridge looks back in history to study what happened as the climate changed at the end of the last ice age.
Scientists examining sediment deposited from glacial lakes can pick out annual layers, called "varves," which have accumulated from yearly runoff.
In the winter, when not much melting occurred, very fine, dark particles of clay settled at the bottom of glacial lakes. Lighter layers of sediment were deposited when silt and sand was carried with runoff.
One of the factors controlling the thickness of each varve is the climate which existed at the time of sediment deposition. A warmer climate would produce a thicker layer of light sediment.
"[There] are longer trends over decades or centuries where the climate may be shifting from a cooler period, where there may not have been as much melting in the summers, to a warmer period," Ridge said. "And so you can actually see it take place over centuries in sequences like this."
Sediment deposition will also decrease in cooler periods, when there is less melt-water coming off of glaciers, Ridge said.
"So if we can figure out how to interpret the lake sediment in terms of those things - whether the glacier that's in the lake is advancing or receding, or whether the climate is warming or cooling, controlling the amount of melt-water coming into the lake, you can turn that into a climate record, essentially a temperature record," Ridge said.
Currently, Ridge is working on a project that investigates how the readvancement of a glacier affects the sediment deposited in varves.
He is taking samples from the Connecticut and Merrimack River Valleys. In the former, the river has chewed away at sediment left from an ancient glacial lake.
"On the sides of the valley, you often have preserved benches, or what looks like a plateau, which is the ancient lake floor," Ridge said.
What turns up in his samples are not only sediment records, but also plant fossils and trace fossils left by organisms that crawled or swam across the lake floor.
"One of the things that we've figured out pretty recently is that as the glacier recedes in a glacial lake, organisms inhabit that lake very, very quickly, much faster than we thought, within a century of the ice front actually leaving that spot," Ridge said.
Last summer in the Connecticut River Valley, Ridge collected fossils of plants that currently populate the Northern Canadian arctic.
So can the study of ancient climates and ancient ecosystems help today's scientist understand the mechanisms controlling our planet's warming any better?
Because ocean and atmospheric circulation are both different today than they were thousands of years ago, what's past is not always what's present.
During the time period focused on by Ridge's research, sea level was 100 meters lower than it is today, and the mean annual temperature in the Northeast was about -5 degrees Celsius.
Although the ancient system and the modern one do not map neatly on top of each other, studying the general mechanisms affecting global climate change can still be helpful for researchers studying today's world.
"When you figure out what causes sudden changes in climate or how that climate operates, it gives you a better understanding of how climate operates in general, and you may find out some things that are important to understanding today's climate," Ridge said.
