| There is growing evidence that the climate change will have significant impact on
permafrost, leading to warming, thawing, and disappearance of the frozen ground.
Arctic soils contain 14%-30% of all the carbon stored in soils worldwide, many of
which is accumulated in the Arctic wetlands (Anisimov & Reneva 2006). Wetlands
occupy almost 2 million km2 in the circumpolar region, contain about 50 Gt C,
and because of the high groundwater levels favour the production of methane in
the anaerobic carbon-rich soil layer (Anisimov et al 2005). Methane has 21-times
stronger greenhouse effect than the equal amount of CO2, and there are growing
concerns that enhanced CH4 emission may have significant effect on the global
radiative forcing. The goal of our study was to estimate the potential increase in the
methane emission from Russian frozen wetlands under the projected for the mid-21st
century climatic conditions and to evaluate the effect it may have on global radiative
forcing.
We used digital geographically referenced contours of Russian wetlands from
1:1,000,000-scale topographic maps to calculate the total area (350 000 km2) and the
fraction of land they occupy in the nodes of 0.5 by 0.5 degree lat/long regular grid
spanning permafrost regions. These data were overlaid with the results from predictive
permafrost model (Anisimov & Belolutskaia 2003, Anisimov et al 1999) forced by CCC,
HadCM3, GFDL, NCAR climatic projections for 2050 under B1 emission scenario (ref.
http://ipcc-ddc.cru.uea.ac.uk/ and http://igloo.atmos.uiuc.edu/IPCC/). Ultimately,
we calculated the increase in the amount of organic material that may potentially
become available for decomposition due to deeper seasonal thawing of wetlands in
the Russian part of Arctic. Following (Christensen et al 2003a, Christensen et al
2003b) we hypothesised that the temperature and substrate availability combined
explain almost entirely the variations in mean annual methane emissions. We used the
results of numerous calculations with the full-scale carbon model simulating a large
variety of soil and temperature conditions to derive a simple parameterization that
links the relative changes of methane flux with soil temperature and active layer
thickness:
J2/J1= exp 0.1(T2 – T1) ,
where J – methane flux, T – ground temperature, Hd – thaw depth, subscripts 1 and 2
designate the baseline and future climatic conditions current and the future time
slices.
Our results for the mid-21stcentury indicate that the annual emission of methane
from Russian permafrost region may increase by 20% – 40% over most of the area,
and by 50% – 80% in the northernmost locations, which corresponds to 6–8 Mt
y-1. Given that the average residence time of methane in the atmosphere is 12
years, and assuming that other sinks and sources remain unchanged, by the mid-21st
century the additional annual 6–8 Mt source due to thawing of permafrost may
increase the overall amount of atmospheric methane by approximately 100 Mt, or 0.04
ppm. The sensitivity of the global temperature to 1 ppm of atmospheric methane is
approximately 0.3 oC (Ramaswamy 2001), and thus the additional radiative forcing resulting
from such an increase may raise the global mean annual air temperature by 0.012
oC.
References
Anisimov OA, Belolutskaia MA. 2003. Climate-change impacts on permafrost: predictive
modeling and uncertainties. In Problems of ecological modeling and monitoring of
ecosystems, ed. Y Izrael, pp. 21-38. S.Petersburg: Hydrometeoizdat
Anisimov OA, Lavrov SA, Reneva SA. 2005. Modelling the emission of greenhouse
gases from the Arctic wetlands under the conditions of the global warming. In
Climatic and environmental changes, ed. GV Menzhulin, pp. 21-39. S.Petersburg:
Hydrometeoizdat
Anisimov OA, Nelson FE, Pavlov AV. 1999. Predictive scenarios of permafrost
development under the conditions of the global climate change in the XXI century. Earth
Cryosphere 3: 15-25
Anisimov OA, Reneva SA. 2006. Permafrost and changing climate: the Russian
perspective. Ambio 35: 169-75
Christensen TR, Ekberg A, Strom L, Mastepanov M, Panikov N, et al. 2003a. Factors
controlling large scale variations in methane emissions from wetlands. Geophysical Research
Letters 30
Christensen TR, Panikov N, Mastepanov M, Joabsson A, Stewart A, et al. 2003b. Biotic
controls on CO2 and CH4 exchange in wetlands - a closed environment study.
Biogeochemistry 64: 337-54
Ramaswamy V. 2001. Radiative Forcing of Climate Change. In Climate Change 2001:
The Scientific Basis Contribution of Working group I to the Third Assessment Report of the
Intergovernmental Panel on Climate Change, ed. YD J.T. Houghton, D.J. Griggs, M. Noguer,
P.J. van der Linden, X. Dai, K. Maskell, C.A. Johnson., pp. 349-416. Cambridge: Cambridge
University Press |