Guest Opinion: Dr. Tim Ball
Sometimes people ask how we know what the temperature was thousands of years ago? The answer is we estimate temperature from proxy data or secondary indicators of the climate conditions at the time. Phenology is an important form of proxy research. It is, “the study of cyclic and seasonal natural phenomena, especially in relation to climate and plant and animal life.” Palynology is one of the least known phenologic techniques used for reconstructing past climate conditions.
It involves taking cores in depositional environments, such as bogs or lake sediments then identifying the pollen in each layer. Pollen is the reproductive seed annually spread from a plant and is remarkably hardy, especially in low oxygen environments. It is also unique for each species (Figure 1).
Figure 1: Colorized images
Pollen counts are done in specialized labs with stainless steel surfaces and a negative airflow to preclude contamination. Results show pollen counts against time that reveal changing plant populations. Figure 2 shows a clear format from a bog in Illinois covering 14,000 years of change.
Changing pollen percentages in each layer reflect changing environmental conditions over time. However, just like tree rings, care is required in identifying the cause of the change. Regardless of the method it is critical in historic reconstructions to obtain as many non-correlated indicators as possible.
I was seeking such proxy indicators for climate conditions during the death of Otzi the Iceman on an Alpine Mountain. His frozen body, discovered in 1991, lay preserved at 3,210 meters. Radiocarbon dates placed his demise between 3239 and 3105 BCE (5254 – 5120 before 2015). The climate pattern assumed he was later covered in ice and exposed by modern warming. Pollen became part of the investigation but only after being discovered in his stomach and clothing. There is one comment of interest.
“The pollen found in his intestines indicates that he hiked through “a coniferous forest at mid-elevation.”
Figure 3 shows the Greenland ice core temperature record, which reflects hemispheric conditions. Cores are further north than Otzi’s location but likely approximate general conditions. A black arrow marks the time of Otzi’s demise and suggests 1.5°C warmer than today.
My research and reconstruction of historic treeline movements triggered an interest in the treeline position Otzi knew. The question about why he was so high in the mountains may be less important if it was not far above the treeline.
The climatic similarities between changing altitude and latitude reflect the change of switching the first two letters. Climate zones change in the same sequence moving to the Poles or going up a mountain. The span of each change is greater for latitude than altitude.
The width of the transitional zone separating closed forests from treeless plant communities is not uniform: polar treelines and drought-caused treelines can form very broad transition zones such as parklands with widely spaced trees (Amo and Hammerly, 1993). Conversely, mountain treelines have rather narrow transitional zones (i.e., 100-200 m of vertical extent).
In Otzi’s case (altitude) the distance appears large regardless of the period. Figure 4 shows a map of the location and assumed route, but does not clarify the treeline issue.
A photograph (Figure 5) of the area shows that considerable movement is necessary for the treeline movement in Otzi’s day to be significant.
Figure 5: Red shows Otzi’s location. Scale given by four people on glacier bottom left.
Palynological studies provide indicators of climate change but lack precision because of slow response. The most effective measure is a comparison with today’s situation as a study of “Holocene Treeline Fluctuations” observes.
To assess the magnitude of past climate changes, reconstructions of Holocene treeline fluctuations must be related to modern treeline positions. For estimations of past temperature changes it is assumed that today’s occurrence of trees is in equilibrium with the climate of the past few decades.
An Arctic treeline commentator notes,
Treeline encroachments and retractions can provide global-scale feedbacks to the climate system, and treeline dynamics are therefore of great relevance for understanding global climate variability.
It is clear that the palynological record was too coarse to determine precise location of the treeline, especially since the date of his death was only accurate within 100 years. The following comment is a bizarre mix of material confirming that the IPCC assessment is either wrong or inadequate, yet still buying into the IPCC warming narrative. The almost obligatory plea for funding colors the quote.
It is clear that the position and composition of the timberline ecotone has been sensitive to Holocene climate change. The millennial-scale trends generally reflect gradual decline in Northern Hemisphere insolation from approximately 11% higher-than-present in the early Holocene. Superimposed on this long-term trend are higher-frequency fluctuations related to changes in oceanic circulation, volcanic activity, and solar irradiance or a combination of these factors. It is also clear that anthropogenic climate forcing over the next 100 years is likely to rival or exceed the warmest conditions of the Holocene. Concerns about global warming involve adjustments, collapses, migrations, or extinctions of boreal and alpine life. Surprisingly, relatively few studies have addressed past responses of ecosystems such as treeline communities to climatic change. One of the reasons for avoiding this topic is that accurate studies require independent climatic proxies and very high temporal resolution «10-20 years/sample). To assess how treelines could respond to global change, high resolution studies including macrofossil analysis are urgently needed.
Determination of what was going on 5000 years ago is further complicated because it was clearly a period of significant change.
Figure 6 shows an amalgamated plot of the sequence derived from various sources. It includes a distinction between treeline, (trees 2m tall) and timberline (8m). The interesting change after 5000 BP is the widening altitude difference to the present.
This change after 5000 was evident in a study in the nearby Piora Valley (Figure 7). That study reports the change, labeled the Piora Oscillation was global.
Piora oscillation, named after Piora Valley in Europe where climatic irregularities were first noted. A major break in the climatic regime which resulted in a readvance of Alpine glaciers, a retreat of forests. Elms and linden trees declined in Europe and North America. In northern Europe the oak and hazel declined or disappeared. Changes occurred as far away as the Andes, Alaska, and the Kenyan highlands, so the disturbance was evidently of global magnitude extended throughout the world. 3500 to 3000 BC.
Many attribute this climate change to the development of more organized civilizations.
Lamb notes that this is the time of the rapid spread of New Stone Age cultures in Europe; meanwhile there seems to have been a sudden stimulus to the growth of organized civilization, to deliberate cultivation along with development of the tools necessary for such activities.
This seems contradictory because it occurs when the Earth is cooling as evidenced by the treeline and timberline drop of about 300m (Figure 6).
Then a stunning claim appears about the cause of the retreat that,
The regression of densely forested areas (timberline) in the Alps during the past 5,000 years was primarily caused by human impact, whereas the course of treeline gives a more realistic estimation of the climatic influence (Figure H9) (Figure 6 in this article).
Maybe it was the new technology copper-bladed axe Otzi carried that allowed such massive early human deforestation (Figure 8)?
As one authority notes,
Archaeological experiments have shown that the copper axe was an ideal tool for felling trees and could fell a yew tree in 35 minutes without sharpening.
Otzi undoubtedly cut some yew trees to fashion his bow. However, he and his few fellow axemen must have been very busy lowering the timberline across the entire Alps. Pollen diagrams (Figure 9) the authors use show a decline in all species. The fires they built to keep warm during the period also seem to have influenced glacier length.
Apparently the explanation for the author’s claims of such early and massive human influence is given in their conclusion. First they acknowledge some natural causes
It is clear that the position and composition of the timberline ecotone has been sensitive to Holocene climate change. The millennial-scale trends generally reflect gradual decline in Northern Hemisphere insolation from approximately 11% higher-than-present in the early Holocene. Superimposed on this long-term trend are higher-frequency fluctuations related to changes in oceanic circulation, volcanic activity, and solar irradiance or a combination of these factors.
But then, just like the IPCC CO2 claims, the human impact takes over from all natural causes and is predicted to continue.
It is also clear that anthropogenic climate forcing over the next 100 years is likely to rival or exceed the warmest conditions of the Holocene.
It is possible Otzi was fleeing from political persecution, but he learned, as we have, that there is no safe altitude.
 “Historical Evidence and Climatic Implications of a Shift in the Boreal Forest Tundra Transition in Central Canada”, Climatic Change 1986, Vol. 7, pp. 218-229