To date, the apparent resilience of the atmospheric–oceanic system has been a major factor limiting the rate and extent of change in climate (largely due to the capacity of the oceans to absorb carbon dioxide and heat). However, there is rising concern among climate scientists that, unless the growth in GHG emissions is soon slowed and reversed, continued increase in water temperature will reduce the oceans’ capacity to remove carbon dioxide from the atmosphere.77-78
At present, the oceans remove about a quarter of human-produced carbon dioxide emissions. As a result, the oceans have gradually become more acidic (with a reduction in the pH of surface waters of about 0.1 during the past 250 years). This trend is generally expected to continue, with a further reduction of 0.2–0.3 pH units occurring by 2100. Should this happen, it could have a major impact on the wide variety of marine organisms with carbonate skeletons, notably corals and plankton, thus potentially affecting the entire marine food chain (see Chapter 6: Marine environment).10
However, this remains an area of considerable uncertainty, as evidenced by the work of Law and her colleagues,79 whose modelling did not find a saturating Southern Ocean carbon sink due to recent climate change. Rather, they concluded that, although carbon uptake was reduced by wind forcing, forcing due to heat and freshwater flow resulted in an increased uptake. Debate on this issue is continuing in the scientific literature (e.g. see Zickfeld et al.80 and Le Quéré et al.81).