wise use of mires and peatlands - Peatland Ecology Research Group

192 APPENDIX IAPPENDIX 2MIRES AND PEATLANDS AND THE GLOBAL CLIMATE 1This appendix is a longer version of the “Regulation of the global climate” material in §3.4.3with tables and text supporting the statements in §3.4.3. It discusses how peatlands andpeatland use may influence the global climate.A2.1 INTRODUCTIONThe peat formation process is stronglyinfluenced by climatic conditions, but mireecosystems themselves also affect the globalclimate. This occurs via the so-calledgreenhouse gases they absorb and emit andthe carbon they store.Like a window pane in a greenhouse, a numberof gases in the atmosphere let solar radiation(visible light) pass to the surface of the earthwhile trapping infrared (heat) radiation thatis re-emitted by the surface of the earth. Thistrapping of heat radiation, that wouldotherwise escape to space, is referred to asthe greenhouse effect. Gases that influencethe radiation balance are called radiativelyactive or greenhouse gases (GHG) 2 .Greenhouse gases fall into three categories:■ radiatively active gases such as watervapour (H 20), carbon dioxide (CO 2), ozone(0 3), methane (CH 4), nitrous oxide (N 20), andthe chlorofluorocarbons (CFCs) whichexert direct climatic effects,■ chemically/photochemically active gasessuch as carbon monoxide (CO), nitrogenoxides (NO x), and sulphur dioxide (SO 2)which exert indirect climatic effects throughtheir influence on the atmosphericconcentrations of hydroxyl radicals (OH),CH 4and 0 3, and■aerosols: 10 -6 - 10 -2 mm large fluid or solidparticles dispersed in the air.Even without human interference, the naturalgreenhouse effect keeps the Earth’s surfaceca. 30 0 C warmer than it would be if all solarradiation was simply transferred back tospace 3 . Water vapour (H 2O), carbon dioxide(CO 2), and clouds contribute roughly 90percent to the natural greenhouse effect,whereas naturally occurring ozone (0 3)methane (CH 4) and other gases account forthe remainder. The emission of greenhousegases by human activities causes a changein the radiation balance of the Earth (radiativeforcing).The type of gases that mires and peatlandsexchange with the atmosphere is not alwaysthe same. Different mire types emit differentamounts and proportions of gases. In thecourse of their long-term development, somemire types become spontaneously wetter 4 andthe proportion of emitted methaneconsequently increases. Peatland drainagegenerally enlarges the share of emitted carbondioxide and decreases that of methane,whereas peatland agriculture additionallyleads to a larger emission of nitrous oxide 5 .As all these gases have a different radiativeforcing 6 , the effect on the radiation balanceof the atmosphere differs with mire/peatlandtype and type of exploitation 7 .