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

Climate impacts on environmental systemsmaterial as the concentration of carbonate ionsdecreases. Most, but not all, marine calcifyingorganisms exhibit the same difficulty (Fabryet al., 2008). Furthermore, pH is a measurewhich affects not only inorganic chemistry butalso many biological molecules and processes,including enzyme activities, calcification andphotosynthesis. Thus, anthropogenic reductionsin sea water pH could affect entire marineecosystems. A comprehensive recent study suggeststhat all coral reefs will cease to grow and start todissolve at an atmospheric CO 2level of 560 ppmdue to the combined effects of acidificationand warming (Silverman et al., 2009). This CO 2concentration would be attained by 2050 underhigh business‐as‐usual emissions scenarios. Otherorganisms and ecosystems are likely to havedifferent thresholds.in ocean acidity (defined here as the hydrogenion concentration). This change has occurred ata rate that is about a hundred times faster thanany change in acidity experienced during thelast 55 million years. The current decline in pH isalready measurable at the three ocean time seriesstations that are suitable to evaluate long-termtrends, located offshore of Hawaii, Bermuda andthe Canary Islands. Figure 3.1 shows the time seriesfrom Hawaii, which is the longest and best knownone, and the changes here are similar to those thatare observed at a much shorter time scale in Europe.The measured reductions in surface pH at thosestations match exactly the values calculated on thebasis of increasing atmospheric CO 2concentrations,assuming thermodynamic equilibrium betweenthe surface ocean and the atmosphere (Bates, 2005;Santana-Casiano et al., 2007; Dore et al., 2009).Past trendsIn December 2011, the atmospheric CO 2levelreached 392 ppm, which is 40 % more than thepre-industrial concentration (280 ppm); half of thatincrease has occurred in the last 30 years. OceanpH has been reduced from 8.2 to 8.1 over theindustrial era, which corresponds to a 30 % increaseProjectionsAverage surface-water pH is projected to declinefurther to 7.7 or 7.8 by the year 2100, dependingon future CO 2emissions. This decline represents a100 to 150 % increase in acidity. When atmosphericCO 2reaches 450 ppm, parts of the Southern Oceanwill start becoming corrosive to calcium carbonateFigure 3.1Decline in pH measured at the Aloha station as part of the Hawaii Ocean timeseriespH Hawaii Ocean8.28.188.168.148.128.18.088.068.048.028January 1988January 1990January 1992January 1994January 1996January 1998January 2000January 2002January 2004January 2006January 2008January 2010Measured pH Calculated pH Linear trend (calculated pH)Source: Dore, 2012.Climate change, impacts and vulnerability in Europe 201291