Research
The Archives of Climate Change
Peat bog research indicates solar activity as very important factor
UvA biologist Dr Bas van Geel’s research places him in the middle of a scientific controversy. Are human dealings, e.g. the increasing emission of industrial greenhouse gases such as carbon dioxide and methane, the most important cause of the climate change which we are currently experiencing, or is this not the case? Dr van Geel, who has gathered new data on natural climate change in the past by examining peat bog samples, remains of plants and pollen grain, isn’t so sure. “I wouldn’t be surprised if increased solar activity turned out to be the main cause.”
Tuva, Southern Siberia. In a project financed by the Netherlands Organization for Scientific Research, an interdisciplinary research team of Dutch and Russian scientists are investigating remains of the Scythian culture. These Indo-European horsemen founded a powerful kingdom in southern Russia around 800 BC, so powerful that warriors such as Darius the Great and Alexander the Great were unable to conquer them. Greek colonies along the Black Sea coast were subjected to the authority of the Scythians, who experienced an explosive cultural and economic growth which has puzzled scientists for a long time. After a lengthy archaeological vacuum that lasted for most of the Bronze Age, numerous Scythian grave monuments suddenly appear in an around Tuva about 850-800 BC containing, amongst other artefacts, the highly-developed precious jewellery typical of the Scythians.
What caused the Scythian’s sudden prosperity and population growth in southern Siberia? Dr van Geel’s team of researchers, which includes archaeologists, pollen experts and other biologists, climatologists and carbon 14 specialists, are of the opinion that the ascent of the Scythians was made possible by climate change. This change led to a modification of the landscape, resulting in quick expansion and migration of the Scythians.
Ecological Determinism
Dr van Geel, now back at work again at the Institute for Biodiversity and Ecosystem Dynamics at the Universiteit van Amsterdam: “Our hypothesis is that the westerly winds shifted slightly to the south, which led to a cooling of the atmosphere and more precipitation in southern Siberia. On the basis of analysis of fossil pollen grains and other fossil plant remains, dated by means of carbon 14 measurements carried out in Saint Petersburg and Groningen, it is clearly evident that the area changed from being a sort of semi-desert with very few plants into a steppe with abundant vegetation. This gave the area a large capacity for supporting human habitation, which was of enormous advantage to the Scythians, a folk of nomadic horsemen. Attribution of archaeological developments to environmental or climate change, known as ecological determinism, is actually rather old-fashioned, and doesn’t fit in with the views of modern archaeologists. Yet, in the case of the Scythians, we are of the opinion that the climate played a decisive role in the sudden flourishing of their culture and in their expansion.”
The most important results of the Tuva investigation by Dr van Geel’s team have been published in the Journal of Archaeological Science, and will help form a better picture of the climate change that took place in West Europe during this period. A sudden transition from dark peat to lighter coloured peat with a different composition can be seen in western European peat bogs around 850 BC. The dark peat stems from a period with a warm, dry climate, the lighter coloured peat was formed in much moister conditions. Apparently a cooler, wetter period began in western Europe – and therefore also in West Friesland - around 850 BC, during which there was more precipitation and less evaporation. “The climate change which was advantageous to the Scythians was, on the contrary, unfavourable to farmers in areas on the periphery of the Netherlands. For example, rising groundwater as a result of the climate change caused swamps to form on a large scale in areas in West Friesland that had been inhabited by farmers for centuries, making them uninhabitable. Other low-lying areas in the north of the Netherlands also became unfit for habitation during this period.”
Rapid climate change
What caused this rather substantial climate change? And it is unique? “Climate change is the rule rather than the exception’, says Dr van Geel, “A stable climate just doesn’t exist. Ice Ages do not, of course, occur overnight, as the film The Day after Tomorrow suggests. But rapid climate changes can be expected. Since the last Ice Age there has been a whole series of climate changes, and there are strong indications that in the past these changes coincided with the sun’s activity level. Our peat bog investigations have shown that periods of wet climate coincide in time with increasing amounts of the carbon isotope C 14 in the atmosphere. Variations in carbon 14 are, for the most part, caused by changes in solar activity. The amount of gas emitted by the sun – known as solar wind – determines the amount of cosmic rays which can penetrate the earth’s atmosphere. The greater the amount of cosmic rays, the more carbon 14 isotopes formed.”
Plants that form peat deposits do not only react to climate change, they also ‘file’ changes in the level of carbon 14 in the atmosphere. Peat bogs are, thus, wonderful natural archives in which a great deal of information about climate change and its underlying causes is recorded. According to Dr van Geel, research shows that the so-called Little Ice Age (dating roughly from 1300 to 1700 AD) was also caused by variations in solar activity. “On the basis of peat bog research, one of our scientists, Dmitri Mauquoy, determined that during the Little Ice Age cold, wet periods coincided with a reduction in solar activity. And information given by plant remains and carbon isotopes agrees with sun spot counts and historical sources. All those folk out skating in the landscape paintings from that period were, in fact, not painted because the artist thought that would prove an interesting subject: during the winters of that period everything iced up for weeks, or even months.
Changes in solar activity
Changes in solar activity are, however, so small that they cannot be the only explanation for climate change. This is also the main reason why a working group of the Intergovernmental Panel on Climate Change (IPCC), who brought out a report in 2001, came to the conclusion that global warming ought to be attributed to human dealings because of the enhanced greenhouse effect during the past fifty years. However, Dr van Geel is not so sure. “I do not deny that an enhanced greenhouse effect is possible, but I wonder whether natural causes aren’t more important than the increased emission of greenhouse gases.
Solar activity has increased unmistakably during the past decades. Dr Mike Lockwood of the Rutherford Appleton National Laboratories in California has shown that the magnetic field of the Sun has doubled during the past century. And it is remarkable that from 1940-1965, when the average temperature remained more or less stable, the emission of greenhouse gases increased while solar activity, like that of the temperature, stagnated. It is, however, difficult to extricate both factors – increased solar activity and enhanced greenhouse effect. The increase in solar activity coincidentally keeps pace with the increase in greenhouse gases. There are, however, a number of mechanisms which perhaps intensify the effects of solar activity, and which have not yet been investigated sufficiently.”
Fluctuations in UV radiation
According to Dr van Geel, for example, even small changes in solar activity can cause rather large fluctuations in UV radiation. ‘UV radiation plays an important role in the formation of ozone in the atmosphere: the ozone layer is thicker when the sun is more active. Ozone absorbs energy from the sun, i.e. warmth. Changes in heat absorption may then lead to shifts in wind circulation patterns and thus contribute to climate change.
Using computer models, the British researcher Joanne Haigh has calculated that the atmospheric circulation system of which the monsoon is a part becomes stronger in proportion to the amount of solar activity. It is, thus, possible that when solar activity decreased around 850 – 800 BC, the influence of the west winds shifted to the south, to the advantage of the Scythians. Anyway, it would be a good thing if physicists and meterologists concentrated more on research into the possible amplifying mechanisms for solar activity. I know that a number of scientists now find this an interesting subject, but interest is not sufficient!
Collective delusion
At present, Dr van Geel is first concentrating on more biologically oriented research. In collaboration with VU colleague Jelte Rozema, UvA postdoc Dan Yeloff is investigating changes which take place in the chemical composition of fossil pollen grain when exposed to UV radiation. Since pollen grain produce substances (phenol groups) which filter out the harmful UV rays, it will probably be possible to chart changes in UV intensity in the past on the basis of the presence of substances from the phenol groups in fossil pollen.
Dr van Geel: “I think it possible that the theory that human dealings are the main cause of the current climate change will turn out to be some kind of collective delusion. However, I have nothing at all against a no-regret policy. There are good geopolitical reasons to restrict the use of fossil fuels and a reduction in the emission of greenhouse gases will certainly improve the quality of the atmosphere. However, the credibility of science is at issue. It would not surprise me if solar activity turns out to be the most important factor determining our climate at present. We must take care that we don’t all run along with the wrong hypothesis, just as twenty years ago when acid rain was indicated as being the main cause of large-scale dying off of forests. Later on it turned out that this was mainly the effect of a number of dry summers.”