CO₂ Levels Over a Hundred Thousand Years
An ice core is a cylinder of ice that has been drilled from a glacier or ice sheet. It acts as a climate time capsule by trapping air, dust, and volcanic ash in layers of snow from past years. Now that we've seen how little air and specifically CO₂ becomes trapped in glacial ice, let’s explore what scientists can learn from the data.
Full view.
This chart shows how atmospheric CO₂ levels change over time
by comparing two different ice cores. Each line represents a
separate core, with gas age on the horizontal axis and CO₂
concentration on the vertical axis. Here, Core 3 represents
EPICA Dronning Maud Land and Core 4 represents Talos Dome,
both sites are located on the Antarctic ice sheet.
Review of Glacial and Interglacial CO₂ Cycles
The "Inhale".
During this part of Earth's climate cycle, atmospheric CO₂ sinks to some of its lowest levels. Over thousands of years, CO₂ levels fall as the planet cools and carbon is drawn into the deep ocean. Ice core records illustrate how this "inhalation" is slow and persistent, acting as a long breath inward that sets up the dramatic rise in CO₂ that follows. During this phase of the glacial cycle, atmospheric CO₂ reaches it's lowest levels.
The "Exhale".
After thousands of years of declining CO₂ levels, Earth begins to warm up as carbon is released back into the atmosphere. Similarly, this rise is steady as it is driven by the ocean circulation changes as well as the retreating ice sheets. Ice core data reflects that CO₂ climbs sharply during this phase, representing a long breath outward that pushes the planet out of its glacial state.
Return to full view.
Over the last 120,000 years, these inhale–exhale swings have repeated with remarkable consistency. Each cycle ends in a warm peak like the one we are in right now — and every time the planet reaches one of these peaks, the next phase is always the same If Earth continued its natural rhythm, we would expect the next “inhale” to begin soon. But does it?
A Vertical Look Inside the Ice Core
Now that we’ve seen how CO₂ changes over time at a large scale, let’s examine how CO₂ is preserved vertically inside a single ice core.
Interactive Depth Explorer
Move the slider to travel deeper into the ice core. Switch between cores to compare CO₂ patterns. You can also click and drag on the chart to select a region and view its average CO₂, depth, and age.
Depth: — m
CO₂: — ppm
Gas Age: — years
What Does This Tell Us?
Based on the data above, we can see that the depth of the ice core correlates with the age of the gas recorded at the time. Now that we have seen how depth correlates with CO2, let's take a look at where we currently are.
So Where Are We Now?
Ice cores show that even the warmest glacial peaks topped out around 280 ppm of CO₂. This last view uses modern measurements from Mauna Loa Observatory (1958–today) to show how quickly we’ve moved beyond that natural range.
Final Takeaways
The CO₂ in the air bubbles that are trapped in ice cores have a lot to tell us about the past and present. As illustrated above, CO₂ levels have naturally increased and decreased in distinct cycles throughout Earth's history. However, in recent years, CO₂ concentrations have risen far beyond their regular range due to increased human activity. We should be expecting another "inhale" period to begin soon, but the sharp increase in our atmospheric CO₂ breaks this historic cycle.
To add to this break, we also note the correlation between the depth of the ice core and the age of the gas. We observed that the older gas tended to have a higher CO₂ concentration than the younger gas. Most significantly, today's atmospheric CO₂ levels exceed the highest concentrations of CO₂ during the warmest periods of the last 120,000 years.
This major change in atmospheric CO₂ concentrations highlight how our current conditions and humanity's quick paced advancements have completely altered Earth's natural cycle that we see preserved in the ice cores. Seeing this exaggerated increase in CO₂ levels in the last few decades, we can predict that our CO₂ concentrations will only continue to rise and the Earth will continue its "exhale" period rather than starting its "inhale".