Ice

Welcome to Antarctica. It's a nice summer day with -27°C. Our mission is to drill down the glacier to get an ice core.
It's like travelling back in time because each layer of ice is from snow that fell a looooong time ago.
ice core 1
ice core 2
ice core 3
We made it all the way to the bottom of the glacier. Let's take a good look at our ice core.
Marker 1
Inside the ice are little air bubbles. Each bubble contains CO2.
 
With those air bubbles we can make a graph of the CO2 levels for the last 800,000 years.
We measure CO2 by seeing how many parts there are for a million air molecules (parts per million or ppm).

Add the right measurements to both points

So what's the difference between 180 and 280 parts per million?