To date, there has been little research into the influence of climate change on the cleanliness and safety of our seas. However, our understanding of possible changes in and the influence of temperature, storms and precipitation allows us to make informed hypotheses about the broad direction of future change. By considering these dominant processes we can also make some assessment of likely changes on a more detailed, regional scale, but very local processes are likely to be the most important drivers of local changes.

Hazardous substances

Changes in future rainfall and winds will have a particular effect on the distribution of hazardous substances in the UK marine environment. For example, unusually wet seasons and intense storm events could deliver untreated sewage and diffuse runoff pollutants from catchments to the coastal and marine environment. Changing seasonal river flow can also change the concentration of treated sewage and the biological oxygen demand could increase as sea temperatures rise. More intense storm events, along with increases in sea temperature and changes in salinity, may also affect the release of contaminants presently in the sediment on the seabed. More indirectly, climate change may lead to increased use of certain pesticides in farming, or of UV sunscreens, and these chemicals could find their way to the marine environment. Changes in storms and rainfall patterns could also affect sewage discharge and the pollution levels in runoff, as well as the disposal of polluted sediments.

Radioactivity

Remobilisation of radionuclides from sediment is now the principal source of caesium-137 and plutonium in the Irish Sea. Changing wind and wave conditions, a potential result of climate change, could further disturb these sediments, leading to the potential remobilisation of radionuclides into the water column and further redistribution.

Eutrophication

The key driver of eutrophication in shelf seas is the supply of nitrate, ammonia and phosphate. Recent studies in offshore North Sea areas show that hypoxic (low oxygen) events in these regions are more likely to be due to climate change than to nutrient enrichment from human sources. Future changes in the intensity of storms and the amount of seasonal precipitation could affect the supply of nutrients in runoff from catchments. Increased stratification in summer could limit nutrient supply to surface waters during the productive seasons, while potentially increasing the occurrence of hypoxic conditions in the bottom waters in deeper parts of the North Sea and Irish Sea. Other pressures such as ocean acidification are likely to complicate the biological responses to nutrient enrichment.

Oil and chemical spills

Climate change could affect the frequency or impact of spills in several ways. Potentially greater storminess increases the chance that oil-bearing vessels will get into difficulties and sink or run aground. More indirectly, changes in agricultural practices or weather patterns might affect the routes and cargo taken by ships. As yet, we have no studies on this covering UK waters, but changes in Arctic sea ice may allow a northern sea-route to become more viable.

Noise

A combination of ocean acidification (as atmospheric CO₂ is taken up by the ocean surface) and reduced ventilation (through a more stable water column) makes the ocean considerably less able to absorb sound for frequencies below about 10 kHz. The previously mentioned projection of an increase in acidity of 0.3 pH units by the end of the 21st century would decrease the capacity of the ocean to absorb low-frequency noise by almost 40%. This would mean that ambient noise levels within the auditory range critical for environmental, military, and economic interests would increase significantly when combined with the potential for increasing sources from human activities.

Microbiological contamination

If higher rainfall increases the amount of faecally derived microbes in the marine environment, this could cause more failures to comply with the values in the EU Bathing Water and Shellfish Water Directives (and worse classifications under the Shellfish Hygiene Directive). Higher temperatures may also encourage the growth of naturally occurring human pathogens such as Vibrios. Both of these effects could increase the health risk associated with recreational water use and shellfish consumption.

Algal toxins

Earlier spring blooms of many harmful algal species could increase their window of opportunity, and warmer waters may allow the expansion of these species into higher latitudes. If warming increases stratification of the seas around the UK, this may also favour such harmful species. There is some evidence that they are more stimulated by nutrients in warmer waters, although this process is poorly understood and could be due to changes in light availability rather than temperature.