SECTOR: ENVIRONMENTAL SCIENCE

The ice age cometh, does a glacier hold the secret of how civilisation began and how it may end?
Inspired by an article by Elizabeth Kolbert published in the New Yorker and reprinted in The Age on March 16th 2002. Supplemented by reviews of original sources as referenced below.

SkilledGeoscience 19th March 2002

"The ice age cometh" was the headline, the subject was the near completion of yet another 3000 meter ice core drill hole through a Greenland glacier. Why?, because earlier work had indicated very rapid paleo climate changes, more detail was needed and the ice sheets in Greenland preserve an exceptionally clear record of past climate.

Like the growth rings on trees glacial ice preserves annual snow falls in centimeter scale layers that show differences between summer snow and winter snow (Figure 1). The relative amount of heavy oxygen (O18) isotope (when compared to the lighter oxygen isotope, O16) trapped in the ice water is a proxy for the temperature prevailing (at sea level) when the water evaporated. Providing each annual snow fall that fell on the glacier was preserved, a 3000 meter hole through such an ice sheet can record the temperature profile of the earth back through time. Quoting from Kolbert' at 42 meters is snow dating from the American civil war; some 760 meters down, snow from the days of Plato", and so on down to 3000 meters and 150,000 years. The profile in Figure 2 records temperature back some 40,000 years based on earlier ice core studies in Greenland. There are several extraordinary events evident in such ice core data. The temperature difference between the last ice age (20,000 years ago) and the start of the warmer and present Holocene period (which began about 10,000 years ago) is about 10 -15 degrees C. However around 15,000 years ago Greenland suddenly warmed by 8.8 degrees in 50 years or less, and around 12,000 years ago the mean temperature in Greenland shot up 8.3 degrees in a single decade. For these reasons there is intense interest in ice core research and the relatively new ( but well established by 1993) science of 'rapid climate change'. An excellent review paper on this subject appears in American Scientist (Taylor 1999). Another notable feature of the ice core plot in Figure 2 is the relative stability of the Holocene (the last 10,000 years) when compared to the wild temperature swings of the last ice age (20,000 years ago) and the transition to warmer climate (20,000 to 10,000 years ago).

The ice story may also hold the secrets about how civilisation began and how it may end. Kolbert quotes insights from her discussion with J.P Steffensen, the leader of the North Greenland Ice Project: "Now you are able to put human evolution into a climatic framework. You can ask 'Why did human beings not make civilisation 50,000 years ago?' You know that they had just as big brains as we have today. When you put this into a climatic framework you can say, 'well it was the ice age'. And also this ice age was so climatically unstable that each time they had the beginnings of a culture you had to move. "Then comes the present interglacial --10,000 years of very stable climate. The perfect conditions for Agriculture. If you look at it, its amazing. Civilisations in Persia, in China, and in India start at the same time, maybe 6000 years ago. They all developed writing and they all developed religion and they all built cities, all at the same time, because the climate was stable. I think that if the climate would have been stable 50,0000 years ago it would have started then. But they had no chance." Said JP Steffensen.

Rapid climate changes are likely to happen again and could affect civilisation as we know it, at least in some areas. Rapid temperature changes in the natural history cycle (Figure 2) dwarf the 0.6 -1 degrees C of global warming measured over the last 200 years, and even the predicted temperature rise over the next 100 years. For example the US EPA suggest a change by the end of 2100 of 1.4 to 5.5 degrees C. Recent global warming has been attributed to post industrial (post 1860) greenhouse gases, at least at the political level. That atmospheric greenhouse gas levels of CH4 and CO2 have experienced unprecedented increase over the last 200 years is fact, and it is also very likely that the cause of the gas increase is mankind. On earth today CO2 levels are higher than in the past 420,000 years and have increased by 31% since 1860. This rate of change is well beyond any natural historic rate. However, the actual cause of temperature rises in the last 200 years is not really known. Over this period there is certainly no 1:1 linear co-varience between the gas levels and temperature; if there was none of us would still be here. So today there is an uneasy imbalance between green house gas levels (which have increased much more rapidly than in the past) and temperature which has not changed a great deal. What can this apparent contradiction mean?. Clearly the correlation that has been made over the full glacial/interglacial cycles between green house gas levels and temperature that have been observed from the Vostock ice core in Antarctica (Figure 3) do not readily apply to the last 200 years nor can they alone predict the temperature increase over the next 100 years. Some more chaotic mechanism is needed to explain past temperature variations and the present anomalous balance. Taylor (1999) discusses the manner of ocean current operation which seems to be analogous to a self organising complex natural system that responds to critical levels or triggers. For example, if the warm north traveling near surface currents in the north Atlantic ocean cannot ultimately sink, the "current conveyor" will shut down and there will be a dramatic climate switch in Northern Europe. Without the warm northward moving surface currents the climate will cool rapidly. The critical factor in future change could therefore simply be melting of the Arctic ice caps. Any signicant increase of freshwater inflows into the north Atlantic could reduce the ocean current density to the point where the currents cannot sink and therefore the entire current (and climate) system reorganises. If no more hot water travels north, how long before the climate changes, one year or 10 years?. It will be rapid.

The scary bit is the ice cores tell us how civilisation may have started and how it may end. We also know what the triggers for critical (and rapid) change could be, but we simply don't know when the critical levels will be reached and precisely how the system will reorganise.

Acknowledgment This article was written by Michael Raetz, part time editor of the Skilled Journal. He is a geologist of some 30 years experience, but he has no particular qualifications in climate or environmental science. This article was inspired by a news feature written by Elizabeth Kolbert originally in the New Yorker which was reprinted in the The Age on 16th March 2002. By the way, "Ice Age" (the movie) is with us now. It opened in the US last week.

The Editor invites discussion about this article or any other matter. For discussion use the forum on www.skilledgeoscience.com New articles for publication in the Skilled Journal are also invited Editor@skilledgeoscience.com