The Regional Impacts of Climate Change

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8.3.6.2. Oceans

An early review (Wright et al., 1986, summarized by Mann, 1993) projected that for the northern Atlantic, some of the consequences of global warming could include:

• A rise in the average sea surface temperature, causing an increase in evaporation and a more vigorous hydrological cycle of precipitation, runoff, and so forth
• The greatest increase in evaporation in mid-latitudes, leading to increased precipitation in northern regions, increased river runoff, increased stability of the water column, and increased strength of buoyancy-driven currents such as the Labrador current
• An increase in the north-south gradient in salinity
• A decrease in the thickness and extent of ice cover
• A reduction of the north-south temperature gradient and possibly a reduction in average wind stress over the whole of the north Atlantic, which could lead to a decrease in the strength of wind-driven currents such as the Gulf Stream.

In their summary of the Symposium on Climate Change and Northern Fish Populations, Sinclair and Frank (1995) described the variability of the northern Pacific in circulation and mixing and linked that variability in part to shifts in atmospheric circulation-specifically, the changes in the location and level of the Aleutian low-pressure system. Existing models have not been able to shed light on the most probable responses of the northern Pacific to a doubling of atmospheric CO₂.

Mann (1993) briefly considered various sources of data for the wind-driven coastal upwelling system off California. He suggested that available data could be used to support the hypothesis that coastal upwelling increases during global cooling but decreases during global warming.

8.3.6.3. Impacts, Adaptations, and Vulnerabilities of Ocean Fisheries Resources

Overall, there likely will be relatively small economic and food supply consequences at the regional/national level; however, impacts are expected to be more pronounced at the subregional level.

Natural climate variability-for example, changes in ocean temperatures and circulation patterns associated with the El Ni�o phenomenon and with the northern Pacific gyre-affects the distribution and composition of fisheries. Because interannual and decadal-scale natural variability is so great relative to global change and the time horizon on capital replacement (ships and plants) is so short, impacts on fisheries can be easily overstated; there likely will be relatively small economic and food supply consequences in the United States and Canada at the national level. At the state or regional level, impacts (positive and negative) will be more pronounced, particularly when a center of production shifts sufficiently to make one fishing port closer to a resource while a traditional port becomes more distant. Over time, fishing vessels and their support structure will relocate, followed by processors and eventually families as well. Community impacts can be significant.

Changes in primary production levels in the ocean as a result of climate change may affect fish stock productivity. As a first step in assessing the role of changes in primary production on fish productivity, global primary production in the ocean has been estimated by Longhurst et al. (1995) using satellite measurements of near-surface chlorophyll fields. Annual global primary production was estimated at 45-50 Gt carbon (C)/year. This annual global primary production is the sum of the annual primary production in 57 biogeochemical provinces covering the world ocean. More than 10 such provinces border North America. For example, the total primary production is estimated at 0.37 Gt C/year in the "California Upwelling Coastal" province and 1.08 Gt C/year in the "NorthWest Atlantic Continental Shelf" province.

Exactly how climate-induced changes in primary production would affect the next trophic link, zooplankton, remains a matter of debate (e.g., Banse, 1995). However, changes in zooplankton biomass are known to affect fish stock productivity. Brodeur and Ware (1995) identified a twofold increase in salmonid biomass in the eastern subarctic Pacific since the 1950s, coincident with a large-scale doubling of the summer zooplankton biomass in the same region. Beamish and Bouillon (1995) examined trends in marine fish production off the Pacific coast of Canada and the United States. They concluded that the carrying capacity for fish in the northern North Pacific Ocean and the Bering Sea fluctuates in response to long-term trends in climate.

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