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A frozen history of Earth’s climate

Glacier ice can be tens of thousands of years old. It traps whatever was in the atmosphere as it formed, freezing and preserving it in layers each year. Paleoclimatologists Lonnie Thompson and Ellen Mosley-Thompson study the cores to learn how Earth’s climate used to be and find clues to how it has changed. Discover what they have found so far.

This photo illustration shows how layers of a glacier hold clues about what was going on in the atmosphere when the layers formed. Numbers reference eight environmental factors that left their mark in the ice core: greenhouse gases, volcanic eruptions, the oxygen isotopic ratio, black carbon, cosmogenic nuclides, insects, dust and pollen.


Greenhouse gases 

Gases that cause climate change are trapped in air bubbles in the ice. By studying the ice, scientists can see how gas concentrations have changed over time. Ice cores show that carbon dioxide levels began rising right after the start of the Industrial Revolution and have continued rising ever since.


Volcanic eruptions 

When volcanoes erupt, they spew ash and sulfate aerosols into the atmosphere, where winds carry them around the globe, depositing some in that year’s ice. Sulfate concentrations in ice cores can provide a timeline of volcanic eruptions.


Oxygen isotopic ratio 

This primary indicator of temperature when a particular section of ice formed helps scientists determine how Earth’s atmospheric temperature has changed over centuries.


Black carbon 

When wildfires burn trees and plants, they release black carbon into the air. Some carbon ends up being trapped in ice, leaving a chronology of fires that occurred near the glacier.


Cosmogenic nuclides

These are rare isotopes that form in the upper atmosphere when it is bombarded by cosmic rays from the sun. Cosmogenic nuclides are trapped in glacier ice; tracing them through an ice core allows scientists to chart changes in the sun’s energy output over time.



Pieces of insects that lived when ice formed can become trapped in glaciers. Ohio State researchers recently proved that fragments from viruses nearly 15,000 years old survived in glacier ice from Tibet.



This indicates droughts and changes in agricultural activity. One core Thompson collected from Mount Kilimanjaro shows a thick black ring of dust from approximately 4,200 years ago, near the time of
a severe famine recorded on a pharaoh’s tomb.



Pollen indicates which plants once existed near the glaciers and how vegetation has changed in a certain region over centuries.

Ice sages 

The research and teaching of Lonnie Thompson and Ellen Mosley-Thompson have one purposehelping future generations beat climate change. See their impact.

Pioneers of paleoclimatology

Learn from the experiences of Ellen Mosley-Thompson and Lonnie Thompson as they reflect on the value of personal identity, facing your fears and forging paths for others. Read more.

Lives in science and service

See how the careers of Ohio State paleoclimatologists Ellen Mosley-Thompson and Lonnie Thompson have grown in tandem with humans’ understanding of climate change. View timeline.

How do you collect an ice core?

Gathering ice from the world’s most remote places takes a team and equipment specially prepared for extreme temperatures and terrain. Follow along on one trip to Peru. See the steps.

About the author

Portrait of author

Laura Arenschield

Laura Arenschield is a science writer with Ohio State. She has covered the Thompsons’ work for more than a decade.