We are currently immersed in the latest ice age, which began about 40 million years ago, triggering the formation of the Antarctic ice mass, which followed the continent's drift to the South Pole about 60 million years before. However for much of the past 150 million years Antarctica has been ice-free, since the original path of the East Australia Current, which today carries warm water southward along Australia's coast, was at that time responsible for keeping Antarctica warm. As the two continents drifted apart, the widening gulf between them disrupted the warm current's flow about 32 million years ago, preventing its heat from reaching Antarctica and plunging the continent into the deep freeze it still experiences today.

This has trapped vast quantities of ice above sea level where it is less prone to melting and better able to reflect the sun's rays, creating a cooling effect. The current ice age subsequently intensified roughly 3 million years ago, triggering the return of the ice sheets in the Northern hemisphere, which had previously melted in an earlier warmer interglacial period. The polar ice caps, in particular the Antarctic ice cap, are crucial to our current climate stability and sea levels.

Warmer interglacial periods occur between ice ages, when there can be near tropical climate conditions lasting for several million years. These warmer periods also occur during ice ages, although they will then be much shorter, on average lasting for about 10 thousand years. During ice ages there are both glacial and interglacial periods when the ice advances and retreats in cycles of typically 40 to 100 thousand years. The Earth entered its current interglacial period 10 thousand years ago, so it's likely that it will be over very shortly, and we will then be plunged into the freezing conditions of the next glacial cycle. Ice ages are generally considered to be caused by changes in the Earth's tilt and elliptical orbit. Some research suggests that our orbit is already reverting to its more elliptical phase, which will shortly trigger a return to an imminent period of glaciation. If this should happen, a colder rather than a warmer future is in store for us, and this would also be accompanied by a substantial reduction in sea level.

Perhaps the ice sheets themselves, or the absence of them, may also control our entry into and exit from ice ages. Our ice sheets historically form and disintegrate in cycles of around 100,000 years, roughly the time required for a continent of ice to form and subsequently melt. There seems to be nothing else in the Earth's calendar that changes on a similar timescale.

Thus regular periods of warming and cooling are normal. Greenland has been significantly warmer in the past, and archaeological evidence of substantial agricultural settlements as recent as 1000 AD has been uncovered. Yet clearly this warmer environment did not result in a catastrophic meltdown, or the extinction of species such as the polar bear. Much is also made of the melting permafrost in the North of Russia, yet today this is melting at only a small fraction of the rate that it was melting 8,000 years ago.

The expansion and contraction of the polar icecaps is quite normal. Cliffs of ice have been falling into the sea during the Spring break up for millions of years, and dramatic movie clips of huge chunks of ice collapsing into the sea do not signify a global warming catastrophe. The falling ice is replenished by compacted snow compressed into ice, which is constantly moving away from the poles towards the equator. We are temporarily in a warming period, when more ice is melting than is being created by compacted snow, and this causes the shrinking of the polar ice cap. The other sections of this site will discuss the probable causes and effects of the current climate changes.