Thursday, 17 January 2002: 2:15 PM
Climate, carbon and the boreal ecosystem
Findings from BOREAS, NOPEX and other studies have led to a greater understanding of the role of the boreal ecosystem in global climate change. These results will be summarized. The boreal ecosystem, encircling the Earth above about 48o N, is and has been intimately connected to long and short-term climate change in three different ways: (1) The boreal ecosystem is composed largely of nutrient-limited conifers growing on cold, moisture-saturated peats that creates an atmospheric boundary layer dry and deep, more characteristic of an arid ecosystem. The deep, dry boundary layers overlying its water-saturated surface have led to its characterization as “a green desert”. (2) Both long and short-term changes in its high-albedo snow and ice extent are linked to global climate variations and coupled to climate through the albedo feedback. Since 1970, climate change has had a significant impact on snow cover, which may have enhanced spring warming through feedbacks from the subsequent decrease in surface albedo. (3) Smoke aerosols produced by extensive lightening induced forest fires modify regional climate by reducing surface insolation and influencing cloud formation and precipitation tendencies. (4) Meridional gradients in atmospheric CO2 concentrations suggest that boreal forests above 40o N sequester as much as 1 to 2 gigatons of carbon annually or nearly 15 to 30%of that injected into the atmosphere each year through fossil fuel combustion and deforestation. Given the enormous areal extent of the ecosystem, roughly 20 million km2 , shifts in carbon flux of as little as 50 gCm-2y-1 can contribute or remove one gigaton of carbon annually from the atmosphere. If the strong high-latitude warming trend continues, leading to warmer soils and a reduction in the extent of the boreal permafrost zone, the resultant increases in soil organic matter decomposition could switch the boreal ecosystem from a long-term carbon sink to a significant carbon source, exacerbating global warming.