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

They use core samples from glaciers which are big rivers of ice that have been around for long periods of time.

But what is a core sample? You may wonder.

Well it’s easy to imagine if you know how it’s made. They use hollow drill pipe where the cutting edges are around the outside of the pipe. So as they cut/drill deeper and deeper, it creates this big long tube of rock inside the drill pipe. When they pull out the drill pipe the inside core sample comes with it and then they push that out of the pipe.

What they’re left with is a long column of ice that they can then analyze. It will show the many different layers of the ice and generally speaking, the deeper they drill, the further back in time they’re going.

However their works isn’t done because you can’t just count the separate layers and think “Ok so 10 layers = 1,000 years” or anything like that. So they have to constantly analyze the core sample to figure out what period of time each layer represents and there can be disagreements about that.

Then once they’ve figured out the time frame for the different layers then they can use what we know about our atmosphered today and compare it with the upper most layers of the ice. Then they can look at 10, 20 or even 50 years ago and what we knew about the atmosphere then and see what’s in the ice.

This way they’re correlating what we know about recent history to what has been captured in the ice.

So ice cores aren’t going to tell you exactly what’s going on but they give you an indication and when you compare it to the data from today, it gives an estimate of what it was like back during some time period.

However you can’t just use one core sample and make a determination. You need to analyze core samples from all over the world before making these determinations. Because CO2 levels may have been higher in the northern hemisphere than the southern for a period of time and that makes a difference in estimates. Same with east and west continents and core samples.

So the more cores you analyze, from different parts of the world, the more confident you can be in your conclusions.