The Apollo 17 crew snapped this photo of Earth as they traveled to the moon in 1972. NASA/JSC

Scientists have drawn a new roadmap for ocean temperatures and carbon dioxide that could help predict coming climate changes, and they did it using data on what happened in Earth’s seas during the last ice age.

It’s hard to look into the past and see how warm or cold the ocean surface was, but fossils held the answer for the researchers. They analyzed the shells of tiny ancient creatures that lived 125,000 to 18,000 years ago. Scientists combined that with data on atmospheric carbon dioxide levels and sea ice coverage to see how the environment evolved leading up to and into the last ice age, which hit its peak about 20,000 years ago. During that period, carbon dioxide levels in the atmosphere gradually stepped down and the ocean cooled.

One of the scientists on the project, Karen Kohfeld of Simon Fraser University, told International Business Times that better understanding the relationship between these factors can help climate scientists improve their predictions of how today’s environment will evolve.

“It’s why we’re in this, is to try to understand how the pieces all fit together,” she said.

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Kohfeld described the animals that produced the shells as being “the size of the tip of your pen” or “maybe the size of a sand grain.” They lived on the ocean surface but now their tiny fossils are preserved all over the ocean and hold clues about the type of environment the creatures lived in. Some of those organisms can live in cooler water and others thrive in warmer water, for example, so their distribution during different time periods — which the scientists can determine by dating the specimens — tells experts when the water was at those desired temperatures. They also analyzed the chemistry of the shells to figure out what temperature would have supported their makeup.

One way of using chemistry to determine temperature is by measuring oxygen. Elements like oxygen come in variations called isotopes, which have different weights based on the subatomic particles within them. Scientists have found, NASA said, there is more of the isotope known as “heavy oxygen,” which has two extra neutrons at its center, in seawater when the climate is colder.

There are other elements to consider too, like magnesium. Warmer water would translate to more magnesium in the shells.

This Globigerina bulloides is an example of one of the tiny fossilized animals scientists used to determine ancient ocean temperatures. Bruce Hayward/Creative Commons

Studying the geochemistry of the shells to back up the findings rules out the possibility that the animals used to thrive under different climate conditions but have simply evolved since then — a change that would have skewed results.

“Evolution might be an issue over longer time periods, but not … over this short period,” Kohfeld said.

The map of the ocean temperatures does more than just show us how hot or cold the marine environment was leading up to and during the ice age. A study in the journal Earth and Planetary Science Letters found the data indicate sea ice responds most quickly to changing ocean temperature, with the masses around Earth’s poles trapping carbon dioxide from the atmosphere in the ocean. Thousands of years later, that was followed by changes in the global ocean circulation, the effect of which was “like a conveyor belt … wasn’t turning over as fast,” Kohfeld said.

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“What comes out is a remarkably clear picture of how the ocean changed during the last ice age,” the University of Tasmania’s Zanna Chase, the other scientist on the study, said in a statement.

That timeline of how carbon dioxide moved in the ancient ocean could give a view of how the current climate may change — although it would be a window leading down the road.

In about “10 years you’re talking more about wacky weather changes,” Kohfeld said, but this model could provide a template for climate scientists to draw a model for the next maybe 50 to 100 years. “It’s fascinating to bring all these pieces together and try to understand this puzzle of how carbon dioxide enters the ocean.”