Cosmic cycles, not carbon dioxide, control climate

Those who think the political war on carbon will cool the globe or keep climate stable need to study climate history.

Temperatures on Earth dance to a cyclic rhythm every hour, every day, every month, every season, every year, and to every beat of the sun-spot and glacial cycles.

The daily solar cycle causes continual changes in temperature for every spot on Earth. It produces the frosts at dawn, the mid-day heat and the cooling at sunset. It is regulated by rotation of the Earth.

Superimposed on the daily solar cycle is the monthly lunar cycle, driven by the orbit of the Moon around the Earth. These two cycles interact to produce variations in atmospheric pressure and tides, and currents in the oceans and the atmosphere. These are the daily weather makers.

The yearly seasonal cycle is caused as the tilted axis of Earth's rotation affects the intensity of solar energy received by each hemisphere. This produces spring, summer, autumn and winter for every spot on Earth.

Then there is the 22 year sun-spot cycle, which correlates with cycles of floods and droughts. Sunspot cycles are indicators of solar activity which causes periods of global warming and cooling.

Earth's climate is also disrupted periodically by the effects of changing winds, ocean hot spots and submarine volcanism that produce the El Nino Southern Oscillation.

The least recognised but most dangerous climate cycle is the glacial cycle. We live in the Holocene Epoch, the latest brief warm phase of the Pleistocene Ice Age. The climate history of the Holocene, and its predecessor the Eemian, are well documented in ice core logs and other records in the rocks. Each cycle consists of a glacial age of about 80,000 years followed by a warmer age of about 20,000 years, with peak warming occurring over about 12,000 years. Our modern warm era commenced 12,000 years ago, so it is probably nearing its end.

There have been eight warm eras separated by long glacial winters over the last 800,000 years of the Pleistocene. In every beat of this cycle, the vast ice sheets melt, sea levels rise dramatically, coral reefs and coastal settlements are drowned, and forests and animals re-colonise the higher land released from the ice. Warm climate animals such as hippos, water buffaloes and elephants got as far north as Germany in the last warm era. Then suddenly the ice returned, covering the northern hemisphere as far south as Chicago and London, destroying the forests, lowering the seas, stranding the relocated coral reefs and eliminating unprepared species. (Some dopey grizzly bears got stranded in the Arctic Ice and the most enterprising of them survived to evolve into white grizzlies now called polar bears.)

This regular repetition of natural climate change is partially explained by the Milankovitch cycles relating to changes in Earth's precession, orbit and tilt. These drive variations in solar energy received by Earth and have the greatest temperature effect on the large land masses of the Northern Hemisphere.

On an even longer time scale, oscillation of the solar system through the plane of the Galaxy seems to trigger magnetic reversals and violent spasms of volcanism, crustal movements glaciation and species extinction. Earth is never still for long.

What about the role of carbon dioxide in climate? Al Gore did a great job to dramatise the recurring glacial cycles in his widely acclaimed work of science fiction. But he missed two inconvenient truths.