Rises in carbon dioxide naturally followed rises in temperature in the ice ages; today the situation is different. Man-made carbon dioxide emissions are driving the global rise in temperature.

This question is based on a misunderstanding of how climate change is happening today. In the last two million years, changes in the Earth's orbit around the Sun caused the fluctuations in temperature that led to the ice ages which, in turn, drove changes in levels of carbon dioxide in the atmosphere. This sequence of events is inferred from ice cores which show that rises in temperature came first, and were then followed by rises in levels of carbon dioxide up to several hundred years later. The reasons for this, although not yet fully understood, are partly because the oceans emit carbon dioxide as they warm up and absorb it when they cool down and also because soil releases greenhouse gases as it warms up.

However, we know that the recent steep increase in atmospheric carbon dioxide (30 per cent since 1900) is not the result of natural factors. Analyses of the different carbon and oxygen isotopes (different physical forms of atoms) prove that the majority of this carbon dioxide has come from the burning of fossil fuels (carbon dioxide from other sources has a different mix of isotopes). The carbon dioxide from human sources is almost certainly (9 chances out of 10 that it is correct) responsible for most of the global warming over the last 50 years. There is much evidence that backs up this explanation which, contrary to the ice age situation, means that since about 1750 carbon dioxide emitted by mankind has been driving the warming and not vice versa; there is no known evidence that conflicts with this explanation.