A new ice age (2)

Earth's orbit is far enough away from the sun that, without help, the planet would be too cold for liquid water and there would be no life as we know it.

Without carbon dioxide and other greenhouse gases in our atmosphere, we would have difficulty surviving. Mars has almost no atmosphere and therefore little ability to retain heat. As a result it is far colder than its distance from the sun would suggest. The temperature on Venus - at some 900 degrees Fahrenheit - is far hotter than its distance from the Sun would suggest: a runaway greenhouse effect is the cause.

Earth's atmosphere, historically, has acted as a thermostat and, for billions of years, has generally kept the planet at a temperature which permits carbon and water based life to exist.

The Vostok Project, completed in 1999, involved drilling into the Antarctic ice. Scientists recovered cores (going back 400,000 years through four complete glacial cycles) and were able to match atmospheric CO2 levels to temperature. The CO2 levels in the record were as low as 180 parts per million in the cold periods (i.e during ice ages) and reached 280 in the warm periods but never higher. Current CO2 levels are now in excess of 380 ppm so we can expect a very warm period in the near future.

By emitting so many greenhouse gases, we are conducting a massive experiment on our planet. Although there are many who doubt that the increasing levels of greenhouse gases put our way of life at risk, the burden of proof must be theirs. The risks of continuing along our present path are existential.

On the other hand, should we totally abruptly abandon the use of fossil fuels, it would not take all that many years, at least in terms of geological time, for atmospheric CO2 levels to drop precipitously. Global cooling and a new ice age would soon be the climate problem at hand.

Caution is necessary but inaction may be fatal.