Perhaps carbon dioxide increases are postponing the next ice age

There’s a lot happening at the moment that attracts my attention — Jennifer Marohasy’s continuing winkling of the Bureau of Meteorology’s apparently dodgy ‘adjustments’ of Australian temperatures, the possibility that a private member might introduce a bill to deal with Section 18C of the Racial Discrimination Act, and a real dialogue between the orthodox and the dissenters on one of the IPCC’s central tenets — to list just three. But I feel the need to acquaint readers with the Ruddiman hypothesis, which I have just discovered.

The late Donald Horne said of Paul Keating that nothing existed for Paul until he had discovered it himself, whereupon he had to tell you all about it. I confess that with respect to Ruddiman I must suffer the same taunt. William Ruddiman is a palaeoclimatologist at the University of Virginia, who has earned a number of medals and distinctions for his work.

For those who don’t know, and I hope there are at least one or two, the Ruddiman hypothesis, which he presented in 2003, is that human interference with the climate through greenhouse gas emissions did not begin with the industrial revolution, let alone more recently from 1950, but started a very long time ago, 8,000 years before the present, with the move into agriculture by our ancestors. Once hunter-gatherers settled down and began to farm they cleared forests and burned the forests, which added to carbon dioxide in the atmosphere. Those in Asia began to create rice paddies, again by clearing land. All of them began to assemble herds of animals, whose numbers also increased.

Ruddiman has proposed that in inter-glacial periods, like ours, carbon dioxide and methane tend to rise to high levels at the beginning of the warming period, and then decline slowly, along with a diminishing global temperature, until the next ice age. He used Vostok ice-core data to suggest that in our inter-glacial something very different happened, with carbon dioxide proportions suddenly rising 8,000 years ago and methane following suit 5,000 years ago. He argues that it was on the cards that a new ice age might have occurred in the past, but the CO2 and CH4 levels were too high.

This hypothesis has been challenged, critics arguing either that there can’t have been enough human beings 8000 years ago to have made much difference, or that other natural factors can probably explain the changes in atmospheric composition. Ruddiman has stayed in the fight, and his role in climate science has led to his hypothesis now being called that of ‘the early Anthropocene’.

There is a lot of scientific talk going on at the moment about whether or not our geological period should be termed the ‘Anthropocene’ rather than the ‘Holocene’, on the ground that human beings have played such a role that their influence on the planet should be reflected in the period’s name. The whole episode fascinates me, and it would require a lot of study to acquire any kind of real understanding. But I am aware, as a historian, that when the Domesday Book was published in 1086 the forest cover of England was already as small as 15 per cent, and there is certainly archaeological evidence that the extensive cultivation of rice began several thousand years ago. Chinese records of rice growing themselves go back 4000 years.

Now Ruddiman saw an ice age coming because there is some evidence that the last two inter-glacial periods lasted for about 10,000 years, and the Holocene is agreed to have begun 11,700 years before 1950. Two Belgian scientists, Berger and Loutre, have been arguing a radical and somewhat contrary view, that we may been in for an exceptionally long inter-glacial, of some 50,000 years.

Why? Well, because they have modelled what happens if CO2 rises to about 700 ppm in the atmosphere, and there is no doubt (from their perspective) that this will keep the ice at bay for a very long time. Mind you, B&L also see the Greenland ice cap’s melting several thousand years down the track, and other large climatic events occurring too. But on the face of it, this gives humanity some breathing space.

Two ideas came to me from all this engaging stuff. One is that if Ruddiman is right, then the ‘Anthropocene’, if our time is to be so described, will have to go back a long way, which doesn’t give the ‘Holocene’ much of a role at all. In fact there are people arguing that this inter-glacial has from the beginning been defined by human activity, and that there is no need for the Holocene anyway. I’ll leave that to the jury (there is one, apparently).

The other is that if Berger and Loutre are right, then the whole effort of trying to combat temperature change is pointed exactly in the wrong direction. We should be keeping up the CO2 and CH4 levels, so that the next ice age is postponed indefinitely. I know that others have said this in the past, and that all the signs are that the warming we have had so far has been beneficial.

But if we have 50,000 years to deal with the problem, there may come the time when the scientists of ten millennia ahead will have worked out how to prevent ice ages ever recurring. And it will all be due to us, and our love for farms, beef and fossil fuels!