Ice Cores as Climate Records: Reading an Ancient Atmosphere

Trapped air bubbles from 800,000 years ago still exist, frozen in place. This article covers how ice cores let scientists read that ancient atmosphere directly.

Reading an Ancient Atmosphere

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THE METHOD

Trapped Air & Isotopes

Air bubbles reveal CO2; oxygen-18/deuterium reveal temperature

800,000 YEARS

Antarctica (EPICA)

The longest continuous ice core climate record

~110,000 YEARS

Greenland (GISP2)

A nearly 2-mile-long core, drilled from the ice sheet

~8,000 YEARS

The Himalayan Link

Kedarnath monsoon record matches Greenland’s temperature pattern

The insight: ice and peat records from opposite ends of the planet tell a matching climate story.

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Must Know

• Ice cores are cylindrical samples drilled from ice sheets and glaciers. Layers within them preserve a direct physical record of past climate.
• Trapped air bubbles inside the ice let scientists directly measure the ancient atmosphere’s carbon dioxide levels.
• The ice itself carries a temperature signal. Scientists measure oxygen-18 and deuterium isotope ratios, both reliable temperature proxies.
• The EPICA Dome C core in Antarctica holds the longest continuous ice-core record, extending back roughly 800,000 years.
• The GISP2 core from Greenland’s ice sheet is nearly 2 miles (about 3,053 metres) long, covering at least 110,000 years.

Good to Know

• In 2008, scientists extended the Antarctic CO2 record from 650,000 to 800,000 years, by analysing the deepest 200 metres of the EPICA Dome C core.
• Across all eight glacial cycles in that 800,000-year record, atmospheric CO2 concentration correlated strongly with Antarctic temperature.
• A roughly 8,000-year monsoon record from Kedarnath, in the higher Himalayas, closely tracks the temperature pattern seen in Greenland’s GISP2 ice core.
• Scientists have also drilled mountain-glacier ice cores in the Andes and on Mount Kilimanjaro, alongside the Himalayan and polar records.

Test Yourself

Please wait…

1. What do trapped air bubbles inside ice cores let scientists directly measure?

Ancient ocean salinity

Ancient atmospheric carbon dioxide levels

Ancient volcanic ash composition

Ancient soil pH

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Great to Know

• Measuring CO2 from trapped air and temperature from isotopes gives two independent proxies from the same physical sample. Their strong correlation strengthens confidence in both.
• The Himalayan-Greenland connection matters beyond coincidence. It shows regional climate signals reflecting global patterns, not just local weather variation.
• Ice cores work as climate archives because snow layers compact without mixing. Each year’s snowfall traps that year’s atmosphere, preserved in sequence like the rings of a tree.
• The 800,000-year Antarctic record predates modern industrial CO2 levels by a huge margin. This makes it a crucial baseline for understanding how unusual today’s carbon dioxide levels actually are.