Model Predictions Of Future Change

OGCMs have been used to reconstruct, as well as predict, changes in climate. Forced by the physical dynamics of the ocean and atmosphere, and coupled together with biological models, OGCMs are able to reproduce biogeochemical cycling within the oceans that closely represents present and past observations. These models predict a global average decrease in pH of 0.4 by year 2100 in the surface ocean (Fig. 1c) and of 0.77 by year 2300 under the IPCC IS92 CO2 scenario [3]. Introducing changes in temperature, weathering and sedimentation into these simulations only reduced this maximum decline by 10% [3]. More detailed predictions of both carbonate ion and CO2 concentration for different oceans regions and across latitudinal gradients strongly imply that the polar and sub-polar oceans are particularly vulnerable to ocean acidification [6]. The carbonate ion concentration is already much lower in these regions so they are particularly vulnerable to a reduction in pH [20] such that they will become undersaturated with respect to both aragonite and calcite by 2100 under IS92 CO2 scenarios [6]. Regional models are now being developed to assess the spatial and temporal variability in pH; for example, the future pH of the North Sea is predicted to undergo similar CO2-induced changes to those predicted in the open oceans although coastal and shelf sea pelagic and benthic activities and riverine input are important factors in contributing to a greater variability [10]. Continued uptake of CO2 by the oceans is predicted to cause some areas in the ocean to be completely outside their natural ranges by the year 2050 [10].

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