How Climate Has Shifted Over Millions of Years
A special kind of lake mud from the Russian Arctic tells us that Earth's climate has oscillated in the past.
A lake in the Arctic has a lot to say about our planet's fluctuating temperatures over the last 34 million years. Play NOVA's Polar Lab to see how.
How Climate Has Shifted Over Millions of Years
Published: February 25, 2020
Caitlin Saks: Despite being above the Arctic Circle, Lake El’gygytgyn has never been covered by glaciers. Which means that when sediment—all the material floating or living in the water—settled on the bottom of the lake, it formed layers that have remained undisturbed.
Julie Brigham-Grette: So you start to accumulate sediments at the bottom of the lake, but also what's accumulating in there is organic matter. So anything that's living on the landscape can get washed into the lake. So all of those elements give us a snapshot of what the ecosystem was like. And that ecosystem then can tell us something about the climate at the time.
Caitlin Saks: What pollen counts from the past million years show us is that the climate around Lake El’gygytgyn has been oscillating, or changing, from warmer periods to colder periods, each period lasting thousands of years.
Julie Brigham-Grette: It’s like a detective story doing this work.
Caitlin Saks: And just like solving a mystery, it’s best when you have multiple lines of evidence all pointing to the same conclusion. We can actually take pollen counts and combine it with data from diatoms and those mammoth-poop-eating-fungal-spores to understand how this lake has changed over the last million years. And, we can combine the lake data with similar cores from around the world.
Julie Brigham-Grette: All of those elements give us a snapshot of what the climate was like.
Caitlin Saks: For the last 34 million years, Earth has actually been an ice house with ice at at least one of the poles, year round. And here’s the big lesson that Lake El’gygytgyn has taught us: that even within an ice house, the temperature oscillates between very cold periods, called glacials, when ice sheets extend down over the continents… and warmer inter-glacial periods like today, when there is still ice, but it’s confined to the poles.
The big question is: Why?
Julie Brigham-Grette: It turns out that what drives glaciation for the most part are three changes in Earth’s orbit around the sun.
Caitlin Saks: The orbit can be more oval or more circular. The tilt of the planet can increase or decrease. And Earth’s axis wobbles like a top. These changes occur over tens to hundreds of thousands of years, and they affect how heat from the Sun warms different parts of the planet.
But that’s only part of the story, because the orbital cycles and the position of the Earth can’t explain why the changes in temperature are so extreme, and why they’re global. So what else is going on here? You’re about to find out.
Hosted by: Caitlin Saks
Production by: Ari Daniel & Lorena Lyon
Camera: Emily Zendt
NOVA Labs Editorial Director: David Condon
Additional Visuals: Mitch Butler, Diatoms of North America | Sarah Spaulding, Earth Science and Remote Sensing Unit | NASA Johnson Space Center, Google Earth, Motion Array, Pixabay, Shutterstock, Videoblocks, Wikimedia | CarmelitaLevin
Music: APM
© 2020 WGBH Educational Foundation
