Executive summary ............................................... 1 1. Introduction ................................................... 15 1.1 Context and motivation ......................................... 15 1.2 Concept and definitions ........................................ 19 1.2.1 General .................................................. 19 1.2.2 Greenhouse gases ......................................... 19 1.2.3 Aerosols ................................................. 21 1.2.4 Radiative transfer ....................................... 23 1.2.5 Detection of climate variability ......................... 26 1.2.6 Natural and anthropogenic climate variability ............ 27 1.2.7 The role of land processes in the climate system ......... 27 1.3 The role of models and satellite data .......................... 28 1.4 Cross-cutting issues ........................................... 29 1.5 References ..................................................... 31 2. Global emission sources and sinks .............................. 33 J.G.J.Olivier and J.J.M.Berdowski 2.1 Introduction ................................................... 33 2.2 Synthesis by GEIA and IPCC ..................................... 34 2.3 Project results ................................................ 39 2.3.1 EDGAR version 3 .......................................... 42 2.3.2 Validation of emission inventories ....................... 44 2.3.2.1 Methane emissions in Northwest Europe ............ 45 2.3.2.2 Methane emissions from rice paddies in Southeast Asia ................................... 48 2.4 Sources and sinks .............................................. 49 2.4.1 Carbon dioxide ........................................... 50 2.4.2 Methane .................................................. 53 2.4.3 Nitrous oxide ............................................ 57 2.4.4 Fluorinated gases ........................................ 59 2.4.5 Ozone precursors ......................................... 61 2.4.6 Aerosols and precursors .................................. 65 2.5 Discussion and conclusions ..................................... 68 2.5.1 Inventory quality ........................................ 68 2.5.2 Validation and verification .............................. 70 2.5.3 Contribution to international science and policy ......... 71 2.6 Recommendations ................................................ 73 3. The land-component in the climate system ....................... 79 B.J.J.M. van den Hurk, A.J.Dolman, A.A.M.Holtslag, R.Hutjes, J. van de Kassteele, R.Ronda and R.J.M.Ijpelaar 3.1 Introduction ................................................... 79 3.2 Vegetation and the hydrological cycle .......................... 82 3.3 Vegetation and the carbon cycle ................................ 86 3.4 Snow processes ................................................. 94 3.5 Soil physical processes ........................................ 97 3.6 Summary ....................................................... 101 4. Global energy balance and radiative forcing ................... 105 R. van Dorland, H.M. ten Brink and R.Guicherit 4.1 Introduction .................................................. 105 4.2 Human induced climate change .................................. 109 4.2.1 Well-mixed greenhouse gases ............................. 109 4.2.2 Ozone ................................................... 109 4.2.3 Aerosols ................................................ 111 4.2.4 Clouds .................................................. 111 4.3 Global forcing estimates of aerosols and uncertainties ........ 114 4.4 Regional aerosol forcing ...................................... 115 4.4.1 Direct aerosol effect ................................... 115 4.4.2 Closure of the short-wave radiation balance ............. 118 4.4.3 Indirect aerosol effect ................................. 120 4.5 Forcing estimates of tropospheric ozone ....................... 120 4.6 Clouds .......................... 122 4.6.1 Validation of satellite retrieval algorithms ............ 123 4.6.2 Micro-physical properties of Stratocumulus clouds ....... 123 4.6.3 Lidar observations of cloud geometry and cloud optical parameters ...................................... 124 4.6.4 Cloud radar research .................................... 124 4.6.5 Sensor synergy .......................................... 124 4.7 Relation between anthropogenic forcing, photochemistry and UV-B dose, a cross-cutting issue .......................... 125 4.8 Conclusions ................................................... 127 5. Climate variability ........................................... 135 S.L.Weber, R.Guicherit, H.W. van den Brink, R. van Dorland, H.Dijkstra, W.Greuell, G.J.Komen, G.Konnen, P.-J. van Leeuwen, O. van de Plassche, J.D.Opsteegh, W.P.M. de Ruijter, F.M.Selten, A. van Ulden and J.Vandenberghe 5.1 Introduction .................................................. 135 5.2 The present climate: variability on interannual to decadal timescales .................................................... 136 5.2.1 Nonlinear dynamics of the equatorial ocean- atmosphere system ....................................... 137 5.2.2 Variability on decadal timescales in the North Atlantic and southern oceans ............................ 140 5.2.3 Air-sea fluxes and the upper ocean ...................... 142 5.2.4 Inter-ocean exchange and the global overturning circulation ............................................. 144 5.2.5 Ice sheet balance in central west Greenland ............. 148 5.2.6 An assessment of the influence of variations in solar activity and of major volcanic eruptions on climate ................................................. 150 5.3 The past climate: variability on longer timescales and climatic transitions .......................................... 153 5.3.1 Patterns of low-frequency temperature variability ....... 153 5.3.2 Ocean-climate variability and sea level in the North Atlantic region since AD 0 ........................ 157 5.3.3 Ocean climate variability on longer time scales and paleo climate fluctuations .............................. 159 5.3.4 Rapid climatic warming in the past: reconstruction and modelling ........................................... 162 5.4 The future climate ............................................ 164 5.4.1 Regional climate change and changes in the statistics of extreme winds and surges .................. 164 5.5 Conclusions ................................................... 167 Annex I Forcing estimates and uncertainties ..................... 175 Annex II Formation, sources and composition of ambient fine- en coaresemode particles .......................... 176 Annex III NRP Projects Theme I "Dynamics of the climate system and its component parts" ......................... 177