Estimates of methane emission during the last 125,000 years in Northern Eurasia

Abstract

The concentration of methane in the atmosphere has varied considerably during the last 125,000 years. Boreal wetlands represent one of the main sources of methane emissions into the atmosphere, the rate of which is largely controlled by climate. Changes in climate (mainly in the duration of the frost-free period) and in the extent of wetlands presumably caused variations in the methane production from boreal ecosystems. We chose Northern Eurasia to estimate both climatic changes and the area of methane-producing ecosystems, as it plays a leading role in methane emission. Palaeobotanic and palaeocryological data were used for the reconstruction. The two most recent warm stages: the Holocene Optimum (5500–6000 years BP) and the Last Interglacial Optimum (ca. 125,000 years BP) were studied. During these warm periods, both an area of tundra and the proportion of the wetlands within the boreal forest zone were considerably reduced. On the other hand, a longer frost-free period and higher precipitation would have caused higher methane production. The precipitation rise was apparently in part compensated by an increase in potential evaporation due to higher summer temperatures. Compared to methane emissions of about 9×10 6 t per year from modern forests of Northern Eurasia, emissions amounted to 86 and 44% of modern values for the region during the Holocene Optimum and Last Interglacial Optimum respectively. Under the greenhouse warming expected early in the 21st century, the climatic conditions may lead to a considerable increase of methane emission.