Climate Change 2001:
Working Group I: The Scientific Basis
Other reports in this collection

4.1 Introduction

This chapter investigates greenhouse gases whose atmospheric burdens 1 and climate impacts generally depend on atmospheric chemistry. These greenhouse gases include those listed in the Kyoto Protocol - methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6) - and those listed under the Montreal Protocol and its Amendments - the chlorofluorocarbons (CFCs), the hydrochlorofluorocarbons (HCFCs), and the halons. A major focus of this assessment is the change in tropospheric ozone (O3). Stratospheric water vapour (H2O) is also treated here, but tropo-spheric H2O, which is part of the hydrological cycle and calculated within climate models, is not discussed. This chapter also treats the reactive gases carbon monoxide (CO), volatile organic compounds (VOC), and nitrogen oxides (NOx = NO+NO2), termed indirect greenhouse gases. These pollutants are not significant direct greenhouse gases, but through atmospheric chemistry they control the abundances1 of direct greenhouse gases. This chapter reviews the factors controlling the current atmospheric abundances of direct and indirect greenhouse gases; it looks at the changes since the pre-industrial era and their attribution to anthropogenic activities; and it calculates atmospheric abundances to the year 2100 based on projected emissions of greenhouse gases and pollutants. Carbon dioxide (CO2) is treated in Chapter 3; and aerosols in Chapter 5. The atmospheric abundances of greenhouse gases and aerosols from all chapters are combined in Chapter 6 to calculate current and future radiative forcing. This chapter is an update of the IPCC WGI Second Assessment Report (IPCC, 1996) (hereafter SAR). For a review of the chemical processes controlling the abundance of greenhouse gases see the SAR (Prather et al., 1995) or Ehhalt (1999). More recent assessments of changing atmospheric chemistry and composition include the IPCC Special Report on Aviation and the Global Atmosphere (Penner et al., 1999) and the World Meteorological Organization / United Nations Environmental Programme (WMO/UNEP) Scientific Assessment of Ozone Depletion (WMO, 1999).



Other reports in this collection