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We don't need a time machine to learn from the past (but let us know if you find one)! Air bubbles trapped in ice for millennia and ancient pollen grains can tell us a lot about climate shifts hundreds of thousands of years ago!

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Maybe you remember the first time you saw a dinosaur fossil on display in a natural history museum, or even just a picture of fossils in books and online.

It’s easy to get lost imagining what the world looked like when these stone bones, claws, and teeth were still a part of living creatures. But when scientists really want to take themselves back in time, they don’t just rely on fossils.

There are a lot of slightly less glamorous samples, from ancient grains of pollen to bubbles of air trapped in ice, that can help us piece together older ecosystems. Studying them has even spawned its own field of science, called paleoecology. And paleoecologists aren’t just learning about the past, they’re trying to predict the future.

Researchers find traces of extinct ecosystems in a lot of places, including locked in the layers of sediment at the bottom of lakes. New blankets of sediment are laid down constantly, as nearby rocks and minerals break into tiny pieces. So the muck gets older the deeper you go, and scientists can use these layers to piece together how things have changed over time.

For example, thanks to pollen in cores of sediment that were collected from a lake in Indiana, we know that beech trees became way less abundant in the Great Lakes region of the U. S. starting about 8,000 years ago. Beech trees burn pretty easily.

But in the part of the sediment cores from that time, the patterns of pollen, charcoal, and minerals hint that drought may have killed off these trees, rather than fire. Solving these cold cases doesn’t just tell us about the past, though. We can use the stuff in sediment cores to figure out how climate shifts might be related to changes in whole ecosystems.

And that can give us some important clues about how today’s anthropogenic, or human-caused, climate change might affect our world in the centuries to come. Charcoal particles in lake sediment, for instance, show that the world’s boreal forests, the evergreen forests around the Arctic, were set ablaze during the Medieval Climate Anomaly. This anomaly was a period of unusually warm temperatures that started around a thousand years ago and lasted several centuries.

Back then, the warming was caused by a strong fluctuation in ocean currents that changed how heat was distributed around the globe, which is very different from the changes going on today in the atmosphere. But the warming of the Medieval Climate Anomaly is similar in scale to what we’re going through now. So scientists think that how forests and other ecosystems were affected at the time might be similar to how they’ll be affected by today’s climate change.

This means forests in the north should probably brace for more fire. So if you thought this year’s fire season was bad, history indicates things are poised to go from bad to worse. Clues come from places besides sediment cores, too.

Scientists can take cores from big, old trees and examine growth rings to look at weather patterns over time, since things like rainfall affect how the rings are spaced. By comparing tree rings to historical climate records, paleoecologists showed that oak trees in savannas in the midwestern United States became less sensitive to drought over the 20th century, likely because carbon dioxide levels have been increasing. With more CO2 available, trees and other plants can use it to photosynthesize more.

When plants open up pores called stomata to take in carbon dioxide, though, they typically lose some water because it evaporates. But it turns out that many plants have adapted so that their stomata can take in more CO2 without letting too much water escape. And this, among other things, makes researchers think that climate change will have complex effects that aren’t necessarily predictable.

Thanks to gas bubbles trapped in thick, Arctic ice, paleoecologists also know that the growing amount of carbon dioxide in our atmosphere is totally unprecedented. Ice cores sampled from some places go back an astonishing 800,000 years. And in all that time, atmospheric carbon dioxide levels have never risen this quickly.

So this time, the changing atmosphere could outpace ecosystems’ ability to adapt. This may sound scary, but we’re arming ourselves with knowledge that will help us deal with the challenges ahead. The more we know about how Earth’s ecosystems responded to climate shifts in the past, the more prepared we’ll be.

It’s like that old saying: those who don’t understand the past are doomed to repeat it. And if you want to arm yourself with more knowledge about the past, check out our sister show Eons, which dives deep into all the incredible things that have happened on our planet over the past 4.6 billion years. Just head over to and subscribe.