Geoscience Reference
In-Depth Information
Other data are available with a lower measuring frequency or over
shorter periods than in the three stations mentioned above. We should
also mention the data collected in the Iceland Sea by Olafsson
et al.
[OLA 09], where the decrease of pH in surface waters (-0.0024 units
per year) is much faster than in subtropical regions. The pH decrease
below 1,500 m is 25% of that of surface waters. The depth of the
saturation horizon for aragonite (one of the main forms of CaCO
3
;
see the Appendix, section 5.8) was 1,710 m in 2009. It increased at a
speed of 4 m per year between 1995 and 2005, exposing an additional
800 km
2
of sea bottom each year to water corrosive to aragonite.
5.3. Projections
Attempting to predict the future consequences of the acidification
of oceans requires projections of the future evolution of the carbonate
chemistry. This section, mostly based on Joos
et al.
[JOO 11],
summarizes the most recent estimates. Projections are carried out
using models based on scenarios, which take into consideration the
possible changes in the demography, economy, technology and
environment. Among the scenarios used are SRES scenarios of the
Intergovernmental Panel on Climate Change (IPCC; [NAK 00]) and
the more recent
Representative Concentration Pathways
scenarios
(Representative Concentration Pathways (RCP); [VAN 11]) which
correspond to a set radiative forcing (RF) at the end of the century.
There are four RCP scenarios: two reference scenarios without
mitigation (RF 6 and 8.5 W m
-2
at the end of the century) and two
scenarios with mitigation (RF 2.6 and 4.5 W m
-2
at the end of the
century). The SRES and RCP scenarios have been used in different
models in order to obtain projections of the climate and the carbonate
chemistry.
Figure 5.5 shows the annual and cumulative carbon releases of the
main scenarios. The highest emissions lead to high RF, especially
when mitigation is absent or weak. When there is no mitigation, the
release of greenhouse gases ranges between 70 and 250% of that of
the year 2000. The increase in emissions slows down in the second
half of the century due to a stabilization of the population and
technological advances. The scenarios that include mitigation show a
