Climate Change Threatens Siberian Forests

In Central Siberia alone, fires have destroyed 38 000 km² in the extreme fire year of 2003. In that year the smoke plumes were so huge that they caused air pollution as far as in the United States. An international team of scientists believes that Siberian fires are influenced by climate change. The study was led by the Professor Heiko Balzter of the Department of Geography at the University of Leicester.

Professor Balzter said "Last century a typical forest in Siberia had about 100 years after a fire to recover before it burned again. But new observations by Russian scientist Dr Kharuk have shown that fire now returns more frequently, about every 65 years. At the same time annual temperatures in Siberia have risen by almost two degrees Celsius, about twice as fast as the global average. And since 1990 the warming of Siberia has become even faster than before."

Global warming leads to warmer springs and causes plants to green up earlier. This has already been observed for the UK. Over Russia the scientists found similar trends towards an earlier spring.

The scientists observed 18 years of satellite images of the region, and estimated the timing of the onset and end of the growing season, when the snow has melted and the plants take up carbon from the air during plant growth. From 1982 to 1999 almost all Siberian ecosystems showed an earlier onset of spring. The strongest advance of spring was observed in Urban areas (0.74 days advance per year), Deciduous Broadleaf Forest (0.46 d/a), Forest - Cropland complexes (0.62 d/a), Humid grasslands (0.35 d/a) and Cropland - Grassland complexes (0.45 d/a).

"Central Siberia has a more continental climate. The changes in the timing of spring and also in fire occurrence are linked to temperature changes and a climate pattern that scientists call the Arctic Oscillation" said Professor Balzter. "Towards the East Siberian coast the Pacific plays a more important role, and the El Niño phenomenon together with low rainfall determines what happens to the forest".

In the continental parts of Central Siberia the Arctic Oscillation and corresponding heat waves are thought to control the fire regime, while in East Siberia El Niño conditions and droughts are thought to play a major role.

"Planet Earth is always more complicated than you think", says Professor Balzter, "The lengthening of the growing season that has been described in the scientific literature is a non-linear phenomenon. It is influenced by feedbacks between the atmosphere and the forest, which responds to rising greenhouse gas levels and higher temperatures."

Reference: Balzter, H., Gerard, F., Weedon, G., Grey, W., Combal, B., Bartholome, E., Bartalev, S. and Los, S., 2007,  Coupling of vegetation growing season anomalies with hemispheric and regional scale climate patterns in Central and East Siberia, Journal of Climate 20:15, 3713--3729, doi: 10.1175/JCLI4226