How do scientists determine how much CO2 was in the atmosphere thousands of years ago, and to what level of certainty are they able to perform these calculations?

Question

How do scientists determine how much CO2 was in the atmosphere thousands of years ago, and to what level of certainty are they able to perform these calculations?

In: Earth Science

Answer 1

Ice cores. Where you drill a big hole in the ice and pull out samples.

When Ice freezes, it traps tons of little air bubbles in it. These little air bubbles have the same composition of the overall atmosphere when that sections of ice froze.

So, if you were to go somewhere like Antarctica, and drill down hundreds of feet, you would get to ice that formed a long long time ago, thousands and even hundreds of thousands of years for the deepest cores.

You now have ice that froze a long time ago, and trapped a sample of the atmosphere from that time in it. You have a sample literally frozen in time.

You can then take that to a lab and do an analysis of how much CO2, Methane, O2, and other gasses are present and compare that to levels we see today and from other younger or older ice cores.

Edit: as for exactly how accurate they are I cannot say what the margin of error is. Each scientific study should report their own margin of error. But when you take an overall view over hundreds of studies and thousands of samples taken, this data is accurate enough and the best option we have to make the models and predictions we need.