Continued...

Basic physics tells us that gases with this property trap heat radiating from the Earth, that the planet would be a lot colder if this effect was not real and that adding more CO2 to the atmosphere will trap even more heat.

What is more, CO2 is just one of several greenhouses gases, and greenhouse gases are just one of many factors affecting the climate. There is no reason to expect a perfect correlation between CO2 levels and temperature in the past: if there is a big change in another climate "forcing", the correlation will be obscured.

So why has Earth regularly switched between ice ages and warmer interglacial periods in the past million years? It has long been thought that this is due to variations in Earth's orbit. However, the correlation is not perfect and the heating or cooling effect of these orbital variations is small. It has also long been recognised that they cannot fully explain the dramatic temperature switches between ice ages and interglacials.