Evidence of climate change geography

There have been several hot periods during the Earth's past.

Around 92 million years ago, for example, temperatures were so high that there were no polar ice caps and crocodile-like creatures lived as far north as the Canadian Arctic, external.

That should not comfort anyone, however, because humans were not around. At times in the past, sea level was 25m (80ft) higher than the present. A rise of 5-8m (16-26ft) is considered enough to submerge most of the world's coastal cities, external.

There is abundant evidence for mass extinctions of life during these periods.

And climate models suggest that, at times, the tropics could have become "dead zones", external, too hot for most species to survive.

These fluctuations between hot and cold have been caused by a variety of phenomena, including the way the Earth wobbles as it orbits the Sun over long periods, volcanic eruptions and short-term climate cycles such as El Niño.

For many years, groups of so-called climate "sceptics" have

evidence that global warming is natural

2. what is the evidence of global warming