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Figure 1. Annual anomalies of global average land-surface air temperature (Jones et al., 2001).
The melting of glacial ice and the thermal expansion of ocean water will cause sea levels to rise in future years. While this is unlikely to have a global effect on ocean life, there are some local cases cases where the change might be too fast for ecosystems to adapt. For example, when slow growing corals cannot grow quickly enough to counteract the rise in sea level, reefs can fall below the photic zone and perish (Harley, 2006).
Many biological processes are temperature dependent and could be adversely affected by even a few degrees of temperature change (Harley, 2006). Higher temperature waters, such as those in the tropics have less primary production in the form of phytoplankton, which almost all fish derive their energy from. This results largely due to the fact that a higher temperature gradient prevents upwelling of cool, nutrient rich waters, as is common during the warm periods of the ENSO cycle off Peru and Chile (Harley, 2006). A drop in the amount of primary production causes a drop in the higher trophic levels as well. Therefore, it is reasonable to predict in many cases this will cause the populations of stocks to decrease Addition of fresh water from melting ice caps decreases surface salinities in ocean regions, which can be detrimental to species with low tolerances to changes in salinity (Harley, 2006).
Projected surface temperature changes by 2099. ("Climate Change 2001: The Scientific Basis," 2001)
Climate change has the potential to cause changes in water chemistry, especially with regards to oxygen solubility and the carbonate buffering cycles. Such changes may have drastic effects on certain species. As seawater warms, the solubility of most gases in it decrease. 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 (Bralower, 2002). A significant, eustatic drop in dissolved oxygen levels would detrimentally influence species worldwide. On the other hand, deep waters are generally not saturated in carbon dioxide. The ocean thus has an enormous capacity as a carbon dioxide sink. However, as atmospheric carbon dioxide levels rise, the equilibrium of the carbonate-bicarbonate-carbonic acid cycle will be shifted towards increasing water acidity (Harley, 2006). Ocean acidification would have detrimental effects on sea life, including important calcareous primary producers, such as coccolithophores.
The introduction of fresh water from melting ice caps can also affect thermohaline circulation. Since fresh water is less dense than salt water, it floats on the surface in high latitude regions. This cap prevents the sinking of water in regions of downwelling, thus weakening or stopping the overturn of the ocean. Current models predict that a shutdown of downwelling in the North Atlantic could occur soon and lead to a shutdown of global ocean circulation (Gagosian 2007). A shutdown of global thermohaline circulation is likely to cause rapid and severe changes in climate, with similar changes in temperature to what has been recorded over the past century occurring on the scale of decades (Gagosian 2007).
Warming of the atmosphere is expected to result in intensified atmospheric pressure gradients. There is already some evidence that this has resulted in increased storm frequency and intensity over recent years. Atmospheric conditions are largely responsible for surface currents, which transport water in the surface layers of the ocean where most of the biomass resides (Harley 2006). Modeling predicts that advection, lateral movement of water, will increase as a result of global warming, especially in eastern boundary currents. Increased advection is generally linked to decreased biomass (Harley 2006).
Figure 2. Projected surface temperature changes by 2099. ("Climate Change 2001: The Scientific Basis," 2001)
Climate change has the potential to cause changes in water chemistry, especially with regards to oxygen solubility and the carbonate buffering cycles. Such changes may have drastic effects on certain species. As seawater warms, the solubility of most gases in it decrease. 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 (Bralower, 2002). A significant drop in dissolved oxygen levels would detrimentally influence species worldwide. On the other hand, deep waters are generally not saturated in carbon dioxide. The ocean thus has an enormous capacity as a carbon dioxide sink. However, as atmospheric carbon dioxide levels rise, the equilibrium of the carbonate-bicarbonate-carbonic acid cycle will be shifted towards increasing water acidity (Harley, 2006). Ocean acidification would have detrimental effects on sea life, including important calcareous primary producers, such as coccolithophores.
The introduction of fresh water from melting ice caps can also affect thermohaline circulation. Since fresh water is less dense than salt water, it floats on the surface in high latitude regions. This cap prevents the sinking of water in regions of downwelling, thus weakening or stopping the overturn of the ocean. Current models predict that a shutdown of downwelling in the North Atlantic could occur soon and lead to a shutdown of global ocean circulation (Gagosian 2007). A shutdown of global thermohaline circulation is likely to cause rapid and severe changes in climate, with similar changes in temperature to what has been recorded over the past century occurring on the scale of decades (Gagosian 2007).
Warming of the atmosphere is expected to result in intensified atmospheric pressure gradients. There is already some evidence that this has resulted in increased storm frequency and intensity over recent years. Atmospheric conditions are largely responsible for surface currents, which transport water in the surface layers of the ocean where most of the biomass resides (Harley 2006). Modeling predicts that advection, lateral movement of water, will increase as a result of global warming, especially in eastern boundary currents. Increased advection is generally linked to decreased biomass (Harley 2006).
Climate change will likely change the distribution of many species. For instance as temperature rises, many species will begin shift towards higher latitudes in order to remain under similar environmental conditions (Harley, 2006). This shifting of species allows the introduction of alien species to ecosystems where they were not previously present, which can fundamentally alter ecosystems. For instance, huge swarms of mauve stingers (Pelagia nocticula), which can devastate populations of fish, are becoming common in the waters off of Britain, where they had not been known until recent years (CNN, 2007).
Many biological processes are temperature dependent and could be adversely affected by even a few degrees of temperature change (Harley, 2006). Higher temperature waters, such as those in the tropics have less primary production in the form of phytoplankton, which almost all fish derive their energy from. This results largely due to the fact that a higher temperature gradient prevents upwelling of cool, nutrient rich waters, as is common during the warm periods of the ENSO cycle off Peru and Chile (Harley, 2006). A drop in the amount of primary production causes a drop in the higher trophic levels as well. Therefore, it is reasonable to predict in many cases this will cause the populations of stocks to decrease Addition of fresh water from melting ice caps decreases surface salinities in ocean regions, which can be detrimental to species with low tolerances to changes in salinity (Harley, 2006Climate change will likely change the distribution of many species. For instance as temperature rises, many species will begin shift towards higher latitudes in order to remain under similar environmental conditions (Harley, 2006). This shifting of species allows the introduction of alien species to ecosystems where they were not previously present, which can fundamentally alter ecosystems. For instance, huge swarms of mauve stingers (Pelagia nocticula), which can devastate populations of fish, are becoming common in the waters off of Britain, where they had not been known until recent years (CNN, 2007).
Another adverse effect from global warming is coral bleaching. When corals are stressed by high water temperatures or other effects, they expel their symbiotic zooxanthelle from their tissues. This process deprives corals of the color, as well of their primary source of nutrition. If corals are without their symbionts for too long they can perish from starvation. The impact of coral death can spread through the reef ecosystem. Secondary effects are most obvious in fish, especially among those that feed specifically on corals, such as butterfly fish. These fish were gradually starving to death and the decline in numbers indicated they had also failed to breed in the months and years following the destruction of their reef. As it stands today, more than 30% of coral reefs throughout the world are already severely degraded and up to 60% of corals may be lost by 2030 due to temperature induced bleaching (ARC, 2007). Coral reefs are also threatened by sea level rise. For example, when slow growing corals cannot grow quickly enough to counteract the rise in sea level, reefs can fall below the photic zone and perish (Harley, 2006).
It is also likely that climate change will have severe, direct effects on humans. Thermal expansion of seawater alone is expected to cause a rise of 0.09 to 0.37 m over the next century (IPCC, 2001). This modest sounding rise is enough to threaten many coastal cities. It is also predicted that storms, such as monsoons and hurricanes, may increase in number and intensity as a result of global warming (IPCC, 2001). Global warming can affect land-based agriculture in certain areas by changing precipitation. Desertification is a major threat in areas such as the southwestern United States (IPCC 2001). Increased carbon dioxide levels will also alter the growth rates of crops and weeds. In certain environments, changes in the productivity of traditional agriculture could lead to a changes in fish demand.
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From 2003-2005, along the Northern California Current, on the West Coast of North America, went through a warming period similar to those related to ENSO, El Nino - Southern Oscillation events, however, southern waters were in an ENSO neutral state, accompanied by delayed upwelling and a lower plankton biomass (Peterson, 2006). Paleoclimatic data suggest that upwelling in the California current system is positively correlated with temperature over millennial timescales. Furthermore, upwelling along the California coast has increased over the past 30 years, and these increases are expected to continue. There is also the possibility, however, of the waters becoming increasingly stratified, which would likely result in a decrease in upwelling. It is also fairly certain that advection should increase in the California current (Harley, 2006). The upwelling could have a beneficial effect on the ecosystem if it is not too strong, but advection would likely have an adverse effect. One study links some of these changes to a decrease in the population growth rates of the northern California Chinook Salmon. The Salmon numbers were negatively effected by increases in sea surface temperature, curl, scalar-wind and pseudo-wind stress, while positively effected by increased seasonal upwelling (Wells, 2007).
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