We often hear in the news that CO2 levels have risen or fallen compared to a couple, or even hundreds or thousands of years ago. How do they know what the CO2 levels were thousands of years ago? And how are they so sure in the accuracy of their tests?
In: Chemistry
Ice cores typically.
In areas where it’s cold enough (Greeland and Antarctica) glaciers and the like have layers of ice like tree rings. Snow falls over the winter, melts during the summer, and freezes again creating a new layer.
Each layer has small teeny tiny bubbles or air trapped inside, like you see in ice cubes in the freezer.
They drill down and take up a long cylindical core of ice that can be several meters long. And the extract air from the layers in a clean room (a carefully sterilized room with limited outside particles, which were first created to measure how much lead was in the water and air). Once in the clean room they test the air and measure how much of each gas is present.
Once they get a sample they can test layers at similar depths from different locations worldwide and get an average.
They can do similar things with soil in warmer areas. In the spring, a melt happens bringing a lot of sediment down rivers which collects in lakes. This also collects in layers. They can measure that and look for the remains of algae and the like which feeds on CO2. The more of them they are, the more CO2 was in the air providing food. Which can confirm other results.
Rocks and ice mostly. As sediment turns into rock and snowfall gets packed into ice, some of the air that’s around gets trapped. As more rock and ice gets formed on top it stays trapped in there. Scientists then dig up large core samples where they drill out long cylinders of material, and they can see all of the layers that form year after year. Then they can check how much CO2 was trapped in each layer over time.
They go to the arctic or antarctic. The ice there formed slowly over the last few thousand years, and it trapped air bubbles in layers. They can measure the CO2 in those little air bubbles. They can verify the process with past measurements over the past hundred years or so, and they can look at tree rings over the last few hundred years.
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