North Sea, United Kingdom
Because global warming affects plankton at the base of the saltwater food chain, it also affects fish that eat plankton, disrupting the overall ecosystem. Fishing is an important industry in the United Kingdom and other countries bordering the North Sea, so communities all around the sea are likely to feel the impact of these changes.1
In the North Sea, global warming is affecting plankton and the marine food chain, compounding the pressures of overfishing.3 Future warming is also expected to exert a significant impact on the marine ecosystem, creating further uncertainty for the fishing industry.7,8,15
Bridlington, Whitby, and other English coastal towns have long depended on the North Sea fishery for food and income.2 But global warming is affecting plankton and changing the marine food chain, compounding the pressures of overfishing.3 The resulting disruption of the ecosystem could damage the fishing industry and hurt North Sea coastal communities from the United Kingdom to Scandinavia.
Plankton anchor the marine food chain. Phytoplankton, which live close enough to the water's surface to perform photosynthesis—critical to maintaining oxygen in Earth's atmosphere—form the base of the marine food web.4 Although phytoplankton are microscopic, they can be seen from satellites when they grow in a concentrated area (bloom) on the ocean's surface.5 Zooplankton, which feed on phytoplankton, and bacterioplankton, which recycle nutrients in the water, make up the next levels of the web.4
Plankton are particularly sensitive to climate change. Since 1950, global mean sea surface temperatures have risen roughly 1° F (0.6° C).6 Scientists estimate that regional sea surface temperatures in the North Sea increased by 1.6° F (0.9° C) from 1958 to 2002.7
The result is changes in the distribution and abundance of plankton species, as well as shifts in their seasonal cycles.3 For example, in the northeast Atlantic, both warmer-water and colder-water plankton moved 10° latitude farther north over a four-decade period at the end of the twentieth century.3,8
The changes have not been uniform, however. While some types of plankton bloomed 30 days earlier at the beginning of this century than in the middle of the twentieth century, other types maintained their seasonal cycles throughout that period.7 Mismatches in marine communities and disruption of the food chain are the result.
Warming of the North Sea and its effects on plankton can influence commercially important species further along the food chain that rely on plankton for food. Major changes in plankton could therefore disrupt not only the marine food chain, but also the fishing industry and communities that have invested in infrastructure tied to commercial species in the North Sea, such as cod.9
Indeed, cod have already been negatively affected.3,10 The shifts in plankton ecosystems linked to warmer surface temperatures have produced a poor food environment for young cod (larvae), reducing the chances that they will survive until they are large enough to be harvested.10
The North Sea cod fishery has been declining owing to overfishing since the late 1960s.10 The North Sea cod catch fell 75 percent from 1987 to 2002, for example.11 In the past two decades, Bridlington fishermen shifted to shellfishing,2 but the nearby town of Whitby is still known as the cod capital of the United Kingdom.12 England's coastal communities can ill afford further damage to the fishery from climate change.
What the Future Holds
Further climate change is expected to intensify these effects on North Sea plankton, cod, and marine ecosystems.7 By 2100, scientists estimate that average world sea surface temperatures could rise as much as 5.4° F (3° C) if our heat-trapping emissions continue unabated.13,14
In the North Sea, surface temperatures are projected to increase 3.6-6.3° F (2-3.5° C) by the end of the century, if our emissions continue to rise at current rates.14,15 If we make significant efforts to reduce our emissions, the increase in North Sea temperatures could be limited to 2.7-3.6° F (1.5-2° C).14,15
If our climate continues to warm at today's rate, scientists expect North Sea plankton that respond to temperature cues to bloom even earlier in the coming decades.7 With a growing mismatch in life cycles among various species of plankton, as well as further climate-induced shifts in their abundance and distribution, effects on the North Sea ecosystem—including cod—are projected to be considerable.7,8
If we make deep and swift cuts in our heat-trapping emissions, we may reduce the impact of global warming on the North Sea fishing industry, and give English communities like Bridlington and Whitby more time to adapt.