Climate change, impacts and vulnerability in Europe ... - MemoFin.fr

Changes in the climate system2 Changes in the climate system2.1 Human influence on the climatesystem2.1.1 The climate systemClimate denotes the statistics (average conditionsand variability) of the day-to-day weather over along time period (usually 30 years). In contrast,weather denotes the state of the atmosphere at anygiven time, such as the day-to-day temperature andprecipitation activity.The Earth's climate system is a complex systemconsisting of several closely linked subsystems:the atmosphere, the hydrosphere (oceans, lakesand rivers), the cryosphere (snow and ice), and thelithosphere (soils). The climate system is closelylinked to the other components of the Earth system,such as the biosphere (see Figure 2.1).The climate system is influenced by many factors,such as solar activity, the Earth's orbit aroundthe Sun, atmospheric composition and volcanicactivity. Climate has always been changing as aresult of changes in these factors. For example, thetransitions between ice ages and intermediate warmphases (interglacials) during the last one millionyears were triggered by predictable changes in theposition of the Earth's axis with respect to the Sun,followed by an amplification of the initial changesthrough feedback mechanisms in the climatesystem. In addition to the long-term changes, theclimate is characterised by substantial variability onmultiple time scales. Examples include daily andseasonal cycles but also more irregular multi‐yearand multi-decadal phenomena such as ENSO(El Niño-Southern Oscillation), NAO (North Atlanticoscillation), PDO (Pacific decadal oscillation), andthe Arctic and Antarctic oscillations.Figure 2.1Components of the climate system, their processes and interactionsSource: IPCC, 2007 (FAQ 1.2, Figure 1).Climate change, impacts and vulnerability in Europe 201249