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!



Join the discussion 10 Comments

  • BoyfromTottenham says:

    Hi Don,

    Congratulations – a nice thought-provoking article, as usual. I must say that the Ruddiman hypothesis is new to me, an avid amateur climate researcher. However I tend to disagree with the idea that humans 8000 years ago started the process of raising CO2 levels, for a couple of key reasons – how many people were there on earth 8000 years ago – a tiny fraction of the current billions for sure, and more importantly, the IPCC itself admits that only 3% of current CO2 emissions are caused by humans – the rest is natural – emissions from warming seas = 60% of emissions for example.

    Without even allowing for current energy related technology (power stations, cars, etc.), just multiply the two factors – say 1% of the current population by 3% of CO2 emissions = to me at least the famous three fifths of five eights of bu@@er all impact on total CO2 emissions likely to have been caused by our post-troglodyte ancestors. A great pity though – I’d love to know why ice ages occur – they are sure as hell more dangerous to mankind than us simply reaching the dreaded 400 ppm of atmospheric CO2!

    BTW – have you looked at all into the source of the world’s CO2 level measurement itself? I find the fact that the whole world relies on reports from a single secretive lab somewhere in Hawaii for the gold standard “global level of CO2” as rather ludicrous, and highly suspicious. Not that I’m cynical, at all. I’m way too old for that.


    • 750.organism says:

      Hi BoyfromTottenham,

      8000 years sounds like a long time. But it is 3/5ths of 5/8ths of f**k all.

      I argue that humanity started in Australia and NOT Africa.

      If you wish to quote IPCC figures and computer models then I have one question that I have asked from the very beginning of being made aware of the whole AGW boondogle and that is,

      Tell me the winning numbers of next weeks lottery.

      That’s it. No more no less.

      Until then the IPCC is nothing but a coven.

      All the best


  • BoyfromTottenham says:

    Hi again, Don.

    I love this site – it has a great real-time 3-d graphic of the subterranean earthquakes under the grumbling volcano in Iceland:


    • Don Aitkin says:

      Thanks very much — it’s an unusual eruption, isn’t it.

      There are so many uncertainties in the whole Ruddiman hypothesis that I decided that a brief encounter was all I could afford. But it was fun!

  • DaveW says:

    Hi Don,
    Thanks for the Berger & Loutre link. I hadn’t read this. It will upset the ice age catastrophists and probably makes the AGW crowd grumpy too. I knew about Ruddiman and even like two things about his hypothesis: it doesn’t assume mankind is evil and it is the reductio ad absurdum of AGW. Other than original sin, though, it still rounds up all the usual suspects, e.g. shonky models, trace green house gas control knob, ad hoc adjustments, lack of correlation over time, ignoring ‘natural’ cycles and exaggerating mankind’s ability to affect the climate beyond the data. Ruddiman’s ‘early anthropocene’ hypothesis is based on these two suppositions:

    1. ‘humans reversed a natural decrease in atmospheric CO2 values 8000 years ago [6000 BC] by starting to clear forests for farms’

    It is estimated (Wiki) that 5-10 million humans were around in 6000 BC. If half of them cleared forest for agriculture (the rest being hunter gatherers), then they must have been busy beavers/firebugs to exceed the natural variability caused by wildfire, flood and pests. However, my understanding is that early agriculture developed during the Holocene Climatic Optimum (9-5000 BP) and primarily on flood plains and grasslands (the source of the wild cereals and graziers), not in areas covered by dense forest. Improved climate allowed agriculture to develop: agriculture didn’t improve the climate and early agriculture didn’t require much conversion of forest.

    As the glaciers retreated forests followed and global forest cover was probably increasing as agriculture developed. Even with modern technology, the taiga (almost a third of the world’s forests) is difficult to clear and is not very good farmland. Sustained clearing of other dense forests (as opposed to slash-burn) is a relatively recent phenomenon and requires considerable technology to maintain as productive farmland. As far as I can tell, extensive clearing of dense forests (taiga, deciduous forests, rain forest) has occurred only in the last few thousand years – after Ruddiman’s new glacial epoch should already have started.

    2. ‘[humans] reversed a natural methane decrease after 5000 years ago mainly by beginning to irrigate rice’

    Most methane is produced in wetlands, and rice paddies are a type of wetland, but presumably ancient people were smart enough to use natural wetlands for rice when available and only irrigated when they had to. Estimates (from Wiki) of the total population of humans 5000 years ago (3000 BC) range from 14-45 million and rise to 50-115 million two thousand years later (1000 BC), so at most a few tens of millions of people growing irrigated rice. Is it reasonable to think that a minute amount of the earth’s wetlands represented by irrigated rice paddies at the time could halt and then reverse the methane cycle? This only makes sense if you believe that anthropogenic methane somehow overloaded the system. Given how much methane volcanoes belch out on an irregular basis, I think this is a ludicrous proposition. Domesticated herbivores also cop some of the blame, but human herds came at the expense of the wild herds that would have grazed the same lands. Think of the 30-60 million buffalo (bison) grazing in western North America at the same time, all belching and farting methane as well as any cow.

    • dlb says:

      Sounds sensible Dave W, I’d rather put my money with you than Ruddiman.

      While on the subject of ancient humans and the environment, I think Flannery is spot on suggesting humans are the major reason for the demise of the mega-fauna.

    • Gus says:

      No, the early agriculture developed in response to the end of the Holocene Climatic Optimum caused, supposedly, by the melting of the Canadian glaciers and the discharge of fresh water from Lake Winnipegosis into the North Atlantic… or something like that. This altered the climate, drying it rapidly, and forced hunters and gatherers of the “Fertile Triangle” to settle and develop agriculture, for survival. See “Guns, Germs and Steel” by Jared Diamond for more on this.

      How effective humans may have been in clearing land, say, 6000 BC or so? They could be quite effective, by the power of fire. Remember that Australian Aborigines altered, or helped Nature alter the whole ecosystem of the continent by bringing fire to it.

      I had a similar idea to the one expressed by Ruddiman years ago, when I was still back in Australia, the idea being that as the Moon recedes from Earth, its pull on the Earth tectonics weakens, thus slowing down the recycling of CO2, which then accounts for the CO2 levels dropping disastrously, as you can see, e.g., in Rothman, “Astmospheric carbon dioxide levels for the last 500 million years,” PNAS USA, 99, 4167-4171, 2002… leading to CO2 starvation and ice ages. Indeed, this has been seen in trees recovered from La Brea Pits of Southern California, see
      doi:10.1073/pnas.0408315102. In summary… the Earth is dying. So, Mother Gaea invents humanity and civilization with the specific purpose of getting all the carbon trapped under ground–coal, oil, gas–and putting it back where it belongs: in the atmosphere!

      And there may be some truth in it. It is certain, in my opinion, that burning fossil fuels does no harm to the Earth eco-systems at all. On the contrary, it brings CO2 back, which is then plowed into the biosphere. We know that the biosphere is responding positively already, see, e.g., doi:10.1002/grl.50563.

      But this is not the whole truth. The primary driver of glaciations and of the current warming is not CO2, but the Sun. Regarding glaciations, this is related to Milankovitch cycles, that is to the varying tilt of the Earth with respect to its orbital plane and to the orbital drift. Regarding the current period, this is related to bursts in solar activity, probably in response to Jupiter’s and Saturn’s pull, which then translates into activity responses of varying periods (60 years is amongst them), which, in turn, affects the ocean dynamics, wherefrom the changes ultimately derive.

      In summary: (1) the present day warmings and coolings are driven by the sun and the solar system dynamics and are therefore totally beyond any human culpability or ability to influence; (2) burning fossil fuels is good for the biosphere as it adds badly needed carbon to the system, it is also good for the economy, since it provides us with cheap form of energy; (3) politically and ideologically driven attempts to restrict or even ban the use of fossil fuels are harmful to our economies, our well being, our security even, they are harmful to Nature, and have no positive impact on climate and weather whatsoever.

      • Don Aitkin says:

        Most interesting, Gus. Of course, ‘badly needed’ is from the perspective of living things, rather than from the perspective of the planet. But in general I agree.

  • Gus says:

    Only something like 3% of the observed CO2 increase has anything to do with humanity. The remaining 97% or about is … natural. It is mostly due to ocean outgassing in response to solar heating, also due to outgassing of tropical soils, etc. That nature could not cope with the puny additional 3% is sheer nonsense, yet, such is the *assumption* made by IPCC. Nature eats it all eventually, given time, which is not this long at all. CO2’s atmospheric residence time is only a few years.

    As the world cools, which may well continue, in response to solar activity diminishing sharply this century, so far, most of this CO2 will go back into the ocean, by itself.

    Temperature variations that have occurred in the past 3 millennia or so, the Roman Warm Period, cooling afterwards, then the Medieval Warm Period, cooling again, and finally the Modern Warm Period, which may or may not last, these are all within only a fraction of a degree C, 0.7C since the end of the Little Ice Age, if we are to believe at all the proposed estimates, and they are just this, estimates, because we don’t really know what *global* temperature was 150 years ago. This 0.7C is a mere 0.2% of the absolute temperature, i.e., expressed in Kelvins, of the globe. It’s a tiny, barely measurable, if at all, fluctuation. A typical daily temperature fluctuation can range from 10C to 50C depending on the location. A typical yearly fluctuation in a typical Midwestern town is about 40 deg C. In some places it can be 60C.

    If it gets cold, as many solar scientists expect, and as it is certainly getting in the US (a very cold winter followed by a very cold summer), it may well mean the end of the very brief warm period, and the end of the CAGW theory.

  • […] few months ago I wrote a piece on ‘the Ruddiman hypothesis’, the essence of which was that humans have been altering the climate for a long time, through […]

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