Like any modern sleuth, Julian Sachs looks for minute traces of things when seeking clues to the mysteries he wants to solve. But rather than DNA from bloodstains, his target is molecules from ancient seagoing algae. And rather than focusing on questions such as who dispatched Colonel Mustard in what room, he wants to know what sea and air temperatures were like up to 150,000 years ago.

Why should we care? Sachs’ findings could provide vital clues to what may happen if the climate changes in the years ahead. “Carbon dioxide concentrations in the atmosphere are rising,” notes Sachs, an assistant professor of earth, atmospheric and planetary sciences. “If they rose to similar levels in the past, we want to know how that affected the climate system.”

One of his concerns is how air temperatures have affected massive oceanic currents like the Atlantic’s Gulf Stream. It’s not a trivial one. If the Gulf Stream were to slow or disappear — one potential result of global warming — the result, ironically, could be a drastic cooling along its route.

Areas from Miami to the Canadian coast would feel the chill. Europe would be hit harder yet. “London, on average, is about 15 degrees Fahrenheit warmer that St. John’s, Newfoundland, even though they’re the same latitude,”notes Sachs. “But if the Gulf Stream failed, London would become like St. John’s.”

The reasons the Gulf Stream’s at risk lie in the complex dynamics of the Atlantic. The key, however, is that tropical water which now gets cold and sinks once it nears the Arctic Circle would instead stay warm enough to “float” on the frigid waters below.

How can Sachs’ efforts help predict the Gulf Stream’s future? Climate modelers check their work by seeing how it matches past climate patterns. If a given level of atmospheric CO2 buildup eons ago coincided with a diminished Gulf Stream, it’s likely new buildups could threaten the current again.

To explore this risk, Sachs works with mud. But not just any mud. His clues come from narrow columns of sediment obtained from as deep as three miles down. Each core is 170-plus feet long, or enough to take you back 150,000 years.

Using an automated system he adapted from the pharmaceutical and food industries, he looks for specific “molecular fossils” — submicroscopic traces of algae constituents that drifted to the bottom thousands of years ago — in core samples. The system also lets him identify tiny but crucial differences in the chemical make-up of the target molecules.

Such differences reveal whether the algae from a given era lived in relatively warm waters or in cooler ones. That in turn can tell you what the climate was like, say, off Bermuda — a recent focus of Sachs’ work — at various points in the past.

The work has already yielded disturbing results. “The climate of the subtropical ocean can change very quickly,” he notes, “and I mean on the order of decades. And it can happen in parts of the world where it really matters.”

Sachs explains that ice cores from Greenland have already shown that that frozen land is prone to fast and dramatic climate changes. “What we’ve found is that the exact same climate patterns have also occurred near Bermuda,” he says.

The changes weren’t as drastic as in Greenland: swings of 5 to 8 degrees F. rather than 15 degrees F. “But in terms of impact on society,” says Sachs, “we need to worry more about the Bermuda results than we do about Greenland.”

Yet if such results are troubling, they’re also what keeps Sachs going. “Phenomena like these rapid climate changes are astounding,” he notes. “The earth itself fascinates me, and the more I learn, the more fascinated I get.”