The temperature curve on the graph follows the line of a hockey stick. It begins to curve upwards around 800AD. Until the beginning of the 20th century the upward slope is very gradual. Then the curve accelerates dramatically as the climate becomes warmer. In most climate reports this point is marked in red for emphasis, for instance in the third and latest from the Intergovernmental Panel on Climate Change (IPCC). This was confirmed by Rajendra K. Pachauri, head of IPCC, at a recent presentation held at ETH Zurich (1) .

Many studies now strongly suggest that there is something wrong with this hockey stick model that Michael E. Mann of the University of Virginia published in 1999 in Geophysical Research Letters.

Already two years ago the scientist Jan Esper and his colleagues from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) (2) in Birmensdorf advanced the view that average global temperature around the first millennium must have been higher than indicated by the hockey stick model. Esper reached this conclusion after examining numerous tree samples that show that ideal growth conditions prevailed at the time in question. The results of this examination, published in Science (2002, 295, 2250-2253), met with scepticism from many scientists but were never disproved.

Now, again, a team criticises the hockey stick model. An international panel around Hans von Storch from the University of Hamburg investigated the so-called proxy data of climate models and found that fluctuations in temperature might have been grossly underestimated. The findings were recently published in Science (2004, 306, 679-682). According to his data, as well, the average temperature from 1000AD to 1100AD had to be higher than that indicated in the hockey stick model.

A further challenge to the model now appears in an investigation from Christian Schlüchter, Professor for Quaternary and Environmental Geology at the Institute of Geological Sciences at the University of Berne, lecturer at ETH Zurich and a keen Alpine scientist (3) . In the June issue of the Swiss Alpine Club's (SAC) magazine "Die Alpen" (4) he published the results of research collected over the past ten years, which had previously been published in various specialist publications, amongst others in the Holocene (2001, 11/3: 255-265). In the latter his conclusions hardly caused a stir but they were taken as a provocation in the SAC magazine. Why?

Wood finding: Scientists from Berne dated it.

The Susten pass, as it might have appeared in Roman times, around 2000 years ago. The Stei glacier has retreated to the level of the Tierberg hut (2795 m), the tree level lies clearly higher. Picture: from "Die Alpen“ / Atelier Thomas Richner based on a draft from Christoph Schlüchter.

In the immediate vicinity of the lower Aar glacier in the Bernese Oberland in the high tide deposits of the glacier stream, Schlüchter found–amongst other things-pieces of wood that were between 30 and 60 centimetres thick and the remains of a moor. "The samples we found were rinsed out from under the glacier by melting water. This means, from where there's ice today," explains Christian Schlüchter. This is remarkable in so far as trees and even moor can only have existed in this location if the area covered by "perpetual" ice was significantly smaller and the tree level higher.

To clarify the matter, the Geology Professor examined and carbon dated the samples in the laboratory. What he found was quite astounding: "The age indicated by the data is not a chaotic cloud of data spread over the past 10,000 years but falls into clearly definable time windows," says Schlüchter. "Until now we have managed to identify ten time windows. Taken over the last 10,000 years this means that, for more than half that period, the glaciers were shorter than they are today.“ In other words, since the last ice age our glaciers have rarely been as extended as they are today.

Moreover, Schlüchter draws another conclusion from the results: "Between 1900 and 2300 years ago the lower tips of the glaciers lay at least 300 metres higher than today. At the time of the Romans they would hardly have been recognised as glaciers for the simple reason that their lower reaches lay above the Alpine passes that were used at the time and would not have been an obstacle.“ This would also explain why, in the otherwise very detailed accounts, the Roman chronicles contain hardly any mention of glaciers. Schlüchter says, "These findings call for a fundamental revision of the prevalent view of a relatively strong coverage of the Alps with glaciers since the ice age. Because for long periods the Alps were greener than they are today."

Martin Funk (5) , Professor for Glaciology at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW), looked at Schlüchter's results. "I see no reason to doubt the results and the conclusions overall, at the most a few details“, says Funk explaining that Schlüchter's study only includes data for a relatively recent period (between 500AD and 800AD) with smaller glacier coverage. "This means that one can't actually compare the hockey stick curve with Schlüchter's results. In addition the temperature alone doesn't tell us much about fluctuations in the area and movement of the glaciers. For that we would also need data about changes in precipitation."

Nevertheless, the data from Jan Esper, Hans von Storch and Christian Schlüchter are a further indication that the curve in question would not be as steep as the IPCC has hitherto claimed.

Schlüchter's publication in the SAC magazine–and above all the corresponding illustration of the landscape on the Susten pass, barely 2000 years ago with a green, glacier free Alp and patches of forest–is taken to be a "massive provocation“ by other experts. In an interview in the "Weltwoche" magazine, Wilfried Haeberli, Professor at the Geographic Institute of the University of Zurich is cited as saying: "I think it highly unlikely that the glaciers had disappeared completely 7000 years ago. And as far as the past five thousand years is concerned, it has been well documented that glaciers have never been significantly smaller than they are today."