wise use of mires and peatlands - Peatland Ecology Research Group

196 APPENDIX 2bogsTable A2/5: Global Warming Potential (GWP in kg CO 2-C-equivalents ha -1 year -1 ) of pristinemires using different time scalesfensCO 2sequestration (kg C ha -1 year -1 ) -310 -250CH 4emission (kg C ha -1 year -1 ) 53 297N 2O emission (kg N ha -1 year -1 ) 0.04 0.1Global Warming Potential 20 years 723 5524Global Warming Potential 100 years 45 1724Global Warming Potential 500 years -233 173Other reviews arrive at similar conclusions.Martikainen (1996) concludes that northernpeatlands have a negative radiative forcingeffect on climate (i.e. they “cool theatmosphere”) because the CO 2uptake (bypeat accumulation and biomass production)compensates for the warming effect of theCH 4emissions. Höper (cf. Table A2/5)deduces that over a short time-scale pristinemires contribute to the greenhouse effectwith respect to their CO 2, CH 4and N 2Obalances. Over a 500-year time-scale pristinebogs have a negative global warmingpotential and fens a small positive potential.Similarly Roulet (2000b) concludes:“Canadian peatlands are neither a net sink orsource of GHGs. … For a time horizon lessthan 100 years, Canadian peatlands are asource (GWP for CH 4emissions > sink of CO 2);for a time horizon greater than 100 years, theyare a sink.”Although it should be recognised, that thereare large uncertainties in these calculations,we may provisionally conclude that■■under the present climatic conditions,on a time scale relevant for currentcivilisation, and■ with respect to the combined effects of CO 2,CH 4and N 2O exchange,pristine mires play an insignificant role withrespect to global warming.In this respect, mires do not differ from virgintropical rainforests and other types of“climax” ecosystems, that are in equilibriumwith climate. Like these other ecosystems thathave a large carbon store in their biomass,mires and peatlands have a considerableclimatic importance as stores of carbon,especially in their peat (see below).Recently it has been acknowledged, thatmany more greenhouse gases are emitted bymires including■ Hydrocarbons, that may significantlyimpact ozone, methane and carbonmonoxide in the troposphere. 400-800·10 12g C yr -1 , an amount equivalent to allmethane emissions, are emitted by plants,primarily trees. As the emissions are verysensitive to temperature, the emissionsfrom peatlands in North America andEurasia are expected to significantlyincrease under global warming 35 .■ Dimethyl sulfide (DMS CH 3SCH 3), an“anti-greenhouse gas” that enters thetroposphere and is oxidized there to sulfateparticles, which - as cloud condensationnuclei - influence cloud dropletconcentrations, cloud albedo andconsequently climate 36 .■ Methyl bromide (CH 3Br) and methylchloride (CH 3Cl) 37 , that have a coolingeffect through their ability to destroystratospheric ozone 38 .No quantitative information is available onthe global climatic effects of thesesubstances.