As World Warms, Europe May Cool - Ecosystems at Risk

Despite global warming, the future may see a cooler Europe, and that could wreak havoc upon the continent’s biological and social stability. So says a new study into the ecological and social effects of an ancient climatic event published in this month’s issue of the journal Geology (doi: 10.1130/G25739A.1).

It has been well-established that there was an abrupt period of cooling in the northern hemisphere at the end of the last ice age about 8200 years ago. Previous studies have linked this cooling with the sudden drainage of glacial lakes in northern Canada (Barber et al, 1999). When the surge of fresh water entered the Atlantic, it disrupted ocean currents, leading to relatively rapid cooling in Europe and eastern North America.

J. Pross of Frankfurt University and colleagues set out to learn about the effects of this so-called “8.2 kyr B.P. climatic event” around the eastern Mediterranean. They collected samples of ancient pollen from a site in northern Greece. By determining the plant species to which each sample belonged, the team was able to reconstruct the ancient ecosystem of the area, and thereby infer local temperature and precipitation trends.

The results were startling. Of the pollen examined from before the climatic event, 87% belonged to broad-leaf species, implying that the area was heavily forested. After the climatic event had occurred, the proportion of broad-leaf species fell to only 53% of the total. Many species disappeared completely. This disturbance in the local ecosystem took centuries to recover, and was almost certainly due to the climatic changes calculated by Pross’s team: average temperatures fell by 4°C, and annual precipitation was about 200 mm less than usual.

The researchers also turned to archaeological evidence to determine the effects of the climatic event on people living in the area at the time. They found indicators of massive social upheaval, as villages were abandoned and populations began migrating across southern Europe. The paper also acknowledges other studies which cite the 8.2 kyr B.P. climatic event as a major contributing factor in the collapse of the Akkad and Uruk cultures in the Middle East (Weiss et al, 2001).

Of course, Pross and his team admit that their conclusion may not apply across the whole region. The site of their pollen studies sits in a valley, and so is subject to a different climate than other nearby sites. However, the team’s data fit well with existing models, so there is good reason to believe that the effects described by the paper occurred over a wide area.

At any rate, the implications of the study are clear. The 8.2 kyr B.P. climatic event was a brief period of cooling during an era of overall warming. If the Greenland ice cap continues to melt, the northern hemisphere may soon experience a similar period of cooling. By determining the ecological and social effects of the 8.2 kyr B.P. climatic event, Pross and his team have delivered an important warning to the residents of Europe: take action against global warming, or face a chilly – and less biodiverse – future.

REFERENCES

Barber, D.C. et al. “Forcing of the cold event of 8,200 years ago by catastrophic drainage of Laurentide lakes”. Nature. 1999, vol. 400, pp. 344-348. doi: 10.1038/22504.

Pross, J. et al. “Massive perturbation in terrestrial ecosystems of the Eastern Mediterranean region associated with the 8.2 kyr B.P. climatic event”. Geology. October 2009, vol. 37, no. 10. pp. 887-890. doi: 10.1130/G25739A.1

Weiss, H., and Bradley, R.S. “What drives societal collapse?”. Science. 2001, vol. 291, pp. 609-610, doi:10.1126/science.1058775.