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

Changes in the climate systemHumans have over time exerted an increasinglyimportant influence on the climate system. Earlyhuman activities affected the climate on a local toregional scale only. For example, the large-scaledeforestation in the Mediterranean region duringthe Roman period altered the regional water cycleand may have caused drying of the region. Withthe industrial revolution, however, human activitiesbegan to alter the composition of the atmospherethereby changing the Earth's climate on a globalscale.The main pathway along which humans areaffecting the global climate is by increasing theconcentration of so called long-lived GHGs. Thesegases let visible light pass through but absorb partof the infrared radiation from the Earth, therebykeeping the heat in the system (see Figure 2.2).The most important GHG in the atmosphere iswater vapour; the most important anthropogenicGHGs are carbon dioxide (CO 2), methane (CH 4),nitrous oxide (N 2O) and a number of halocarbons.The atmospheric concentrations of these gases arenow far higher than at any time during the last800 000 years. This is a result of the burning of fossilfuels, deforestation, and to a lesser extent the raisingof cattle and the use of synthetic fertilisers. Thecurrent concentration of CO 2, the most importantanthropogenic GHG, is 392 ppm (parts per million)(NOAA, 2012), compared to a historical range of180 to 300 ppm as measured by air bubbles fromthe last 800 000 years captured in deep ice cores ( 31 ).Further human activities that warm the Earth arethe emission of short-lived ozone (O 3) precursors(nitrogen oxides (NO X), carbon monoxide (CO), andhydrocarbons) and the emission and deposition ofblack carbon aerosols (i.e. soot) on snow and ice,which reduces its reflectivity. Human activities affectalso several other aspects of the climate system,e.g. through agriculture, land-use change, and theFigure 2.2The Earth's energy balanceNote:The magnitudes of variousenergy flows in this figureare associated with someuncertainties. Please consultthe original reference forfurther information.Source: (Trenberth et al., 2009, fig. 1).© American MeteorologicalSociety. Reprinted withpermission.Note:The magnitudes of various energy flows in this figure are associated with some uncertainties. Please consult the originalreference for further information.Source: Trenberth et al., 2009, figure 1. © American Meteorological Society. Reprinted with permission.( 31 ) Note that carbon dioxide emissions have two major impacts. One part ends up in the atmosphere where it increases thegreenhouse effect and thus warms the planet. Another part ends up in the oceans where it increases their acidity. Oceanacidification has potentially severe consequences for marine ecosystems, such as coral reefs (see Section 3.1). It is sometimesdenoted as 'The other CO 2problem'.50 Climate change, impacts and vulnerability in Europe 2012