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Over the past century or so, the earth has seen a significant rise in average global temperatures (see Figure 12). Studies show that average surface temperatures have risen at the rate of approximately 0.1°C/decade, which is significant when compared to estimates of historical values (IPCC, 2001). Regardless of whether this temperature increase is primarily a result anthropogenic causes, such as as emission of greenhouse gases, or natural fluctuations, global warming will have a profound effect upon the oceans and should therefore be of great concern to anyone in charge of managing global fisheries. It is also very likely that global warming will accelerate in the near future due to positive feedback mechanisms, including the lowering of the Earth's albedo due to melting of polar caps (IPCC, 2001). Climate change is quite difficult to monitor, and even more difficult to predict accurately (see Figure 2). accurately Despite this, research on current systems as well as research into past global warming events provides a general idea of what can be expected in future years. Knowledge of these general trends will allow us to better understand the effects and, consequently, better manage fisheries.
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Changes in the temperature of ocean water have the potential to cause significant changes in water chemistry. Addition of fresh water from melting ice caps decreases the salinity of ocean regions, which can be detrimental to species with low tolerances to changes in salinity (Harley, 2006). Also, as seawater warms, its ability to dissolve gases decreases dramatically. One of these gases is oxygen, which is essential to all animals for respiration (Harley, 2006). Geological records from past global warming events has shown evidence of severe, large-scale hypoxic episodes, sometimes reaching global scales (Bralower, 2002). A significant drop in dissolved oxygen levels would have a detrimental effect on many species. Another critical area of seawater chemistry that will likely be affected by global warming is the carbonate buffering system. The ocean have an enormous capacity to take up carbon dioxide. However, as atmospheric carbon dioxide levels rise, the equilibrium of the carbonate-bicarbonate-carbonic acid cycle will shift towards greater amounts of carbonic acid, lowering the pH of the water (HarleyLackner, 20062003). Like temperature, there are many species who are sensitive to even small changes in pH. Ocean acidification would have detrimental effects on sea life, especially important calcareous primary producers, such as coccolithophores, and animals that posses carbonate shells. There is also geological data which indicates build up of toxins in the ocean during intense global warming events (Bralower, 2002).
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