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Regardless of cause, the global climate is getting warmer, and will continue to do so in the future. Projections vary wildly between sources, as demonstrated in the below illustration compiled by the Intergovernmental Panel on Climate Change.
Various temperature predictions ("Climate Change 2001: The Scientific Basis," 2001)
However, all agree on one aspect: the oceans, as a major component of the earth's climate system, will be affected by this change. Such changes would decrease fish populations and biodiversity even if overfishing were not a problem. Many of these changes are relatively imminent, with timescales of about 100 years. Much is unknown exactly how climate will change, placing fisheries in an increasingly precarious position.
Surface temperature change between 1979 and 2004 ("Climate Change 2001: The Scientific Basis," 2001)
Projected surface temperature changes by 2099. ("Climate Change 2001: The Scientific Basis," 2001)
What does this mean for fisheries? Generally, as marine habitat conditions change, they will disrupt the species living in the habitat in a negative manner, since species are already adapted to the habitat in which they reside (Mathews-Amos & Berntson, 1999)
Specifically, projected climate changes will affect the following aspects of ocean environments:
#Decrease/ change in paths of ocean currents -ocean currents depend on specific thermo-haline circulation patterns. Changes in temperature threaten these patterns, both directly and by decreasing salinity due to polar ice cap melting. (Harley, 2006). Most marine fishery ecosystems depend on the conditions these currents provide.
Current ocean circulation patterns. "Line W" refers to a "critical junction" between ocean waters that is being monitored for climate change by the Woods Hole Oceanographic Institution (Mike Carlowicz, 2007).
#Sea level rises - thermal expansion of water (90% of effects) and melting of glacial ice will destroy very depth- dependent ecosystems, such as coral reefs.
#Water composition - Warming seawater can hold less dissolved CO2 and O¬¬¬2, and will have less salinity due to melting ice caps. Increased CO2 levels threaten species by decreasing pH, while increased O¬2 and decreased salt directly threaten species dependent on specific compositions (Harley, 2006).
Projected changes in ocean acidification by the year 2099 ("Antarctica does Acid - global warming, ocean acidification, and the Southern Ocean," 2006).
Perhaps the greatest effect from climate change on global fisheries could be through plankton. Plankton is the basic food source for many of these creatures, including fish larvae (Haysa, Richardsonb, & Robinson, 2005). Plankton must follow ocean currents, and are dependent on certain atmospheric conditions. It has already been found that increasing ocean temperatures affect plankton levels through ENSO cycle studies (Haysa, Richardsonb, & Robinson, 2005). However, whether plankton will be enhanced or depleted by predicted climate changes on a global scale is unknown.
Simulated levels of various plankton species' growth (Follows, Dutkiewicz, Grant, & Chisholm, 2007).
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Duke University. Mining vs. Farming: The International State of the Fisheries. Retrieved 17 November 2007, from the World Wide Web: http://www.biology.duke.edu/bio217/2002/fish/state.html
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National Marine Fisheries Service. (2006). Per Capita Consumption. National Oceanic and Atmospheric Administration: http://www.st.nmfs.noaa.gov/st1/fus/fus06/08_perita2006.pdf.