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Long cylinder of an ice core Long cylinder of an ice core
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What are ice cores? A history of Earth’s climate

Glacier ice, which can be tens of thousands of years old, traps whatever is in the atmosphere as it forms, freezing and preserving these clues in new layers each year. Discover what paleoclimatologists Lonnie Thompson and Ellen Mosley-Thompson have found so far.


1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. Insects 

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.

7. Dust

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.

8. Pollen 

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

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