Climate change is nothing new. The earth’s climate is ever-changing and scientists have the tools to prove it. A few different techniques are used to determine temperatures from millions of years ago when we were nowhere near capable of accurately recording and keeping temperature.

The most reliable way to measure temperatures from many years ago is by observing ice cores obtained from places like Antarctica and Greenland. Climate scientists take big drilling rigs to drill cores of ice up to two miles deep, they are then tested for bubbles of air trapped in the ice.

This ancient air can be measured by scientists for the composition of the gas. They use all of these samples to construct a virtual atmosphere. With these numbers, scientists are able to conclude that temperatures have changed drastically in the earth’s history.

One way the earth’s natural climate change is observed using sediments found deep in the bottom of the seas. These sediments can preserve the shells of small animals for millions of years. One of these animals used and the most important of these ancient fossils is foraminifera or forams for short. These ancient animals make their shells out of calcium carbonate (CaCO3). 

Calcium carbonate is important because it was originally dissolved in oceans and it contains oxygen. This oxygen contains two naturally occurring stable isotopes, 18O and 16O. Scientists can use the ratio of each of these isotopes to determine past temperatures.

This is done because the ratio of 18O and 16O depends on how cold or warm the ocean was at the time of the creation of a new shell. This is the simple explanation and it varies a lot depending on the values of other things in the surrounding seawater.

Using these methods scientists were able to conclude that millions of years ago, pre-ice age, the arctic oceans were 10-15ºC warmer than they are today.