Temperature and CO2

Temperature & CO2 move together

The temperature of the Earth’s atmosphere has moved with the carbon dioxide (CO2 ) level in the atmosphere for at least 800,000 years.

Graph: Temperature and CO2 Level have moved together over 800,000 years
Temperature and CO2 Levels over 800,000 years: NASA Earth Observatory

Graph: NASA Earth Observatory

  • The blue line shows the “carbon dioxide level in the atmosphere” over the 800,000 years before 1950.  (It does not show the rapid rise in CO2 levels, since 1950, to over 400 parts per million (ppm)).
  • The red line shows the “Antarctic air temperature” over this same period.

The two graphs show that the temperature has been high when CO2 has been high – over the last 800,000 years.  Also, when the level of CO2 has been low, the temperature has been low.

This graph is evidence that temperature and carbon dioxide levels tend to move together.

Ice Ages and low CO2 go together

The most recent ice age ended about 20,000 years ago.

Looking at the markings of the time axis on the graph, you can see five periods between 0 and 200,000 years ago, so each period is 40,000 years, and 20,000 years ago is in the middle of the period just to the left of the zero.

So, the graph indicates that when the most recent ice age ended at about 20,000 years ago, the temperature was about minus 5 C and the CO2 level about 180 ppm. This period is an example of a low temperature occurring at a time of low carbon dioxide: an ice sheet up to three kilometres deep covered about half of North America during this ice age.

You can see that there are about ten temperature peaks over these 800,000 years. These are inter-glacial periods which are short periods of warmth.  For most of the time, the Earth has been in ice-ages.

How scientists worked this out

Scientists went to Antarctica and drilled deep into the ice. By examining bubbles of air trapped in this ice, they have seen what has happened in Antarctica over the last 800,000 years.  Scientists measure the CO2 levels in these trapped air bubbles and determine how CO2 moved over this period.  From these air bubbles, they can also identify the atmospheric temperatures.

A little CO2 has a big impact

Some people may think that CO2 levels, like 300 parts per million, are so small that they cannot be influential.  However, the graph shows otherwise. It shows that at 180 ppm, you have an ice age. Changes in CO2 level pack a big punch, just like a small pinch of salt can have a big influence on the taste of a meal.

John Tyndall identified the basic science behind this long ago, in 1863. When you increase the concentration of carbon dioxide in the atmosphere, this decreases the heat escaping from our planet into outer space, which tends to raise temperatures on our planet.

“Global temperature” and the “level of carbon dioxide in the atmosphere” tend to move together.  The vast amounts of carbon dioxide released by burning fossil fuels during our industrial age have increased CO2 levels by a large amount, and this threatens to increase global temperatures by a large amount.  The planet has started to heat, and we need to limit this threatened large change.


The three-minute story of 800,000 years of climate change with a sting in the tail: The Conversation 13 June 2017

Modified 1 March 2020

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