Climate of the marine environment

Ocean climate is largely defined by its temperature, salinity, ocean circulation and the exchange of heat, water and gases (including CO2) with the atmosphere. The functioning of our marine ecosystem is highly dependent on changes to both ocean climate and acidification, whilst storms and waves, sea-level rise and coastal erosion pose clear threats to human life, built structures and shipping.

The bold text indicates new information for the 2007–2008 report.

	WHAT IS ALREADY HAPPENING	WHAT COULD HAPPEN
Temperature (air and sea) BADC; FRS; MOHC; NOCS; SAMS; UKCIP	Marine air and sea surface temperatures (SST) have been rising at a similar rate to land air temperature, but with strong regional variations. Since the 1980s the rate of rise has been about 0.2–0.6 ºC per decade. Warming has been faster in the English Channel and southern North Sea than within Scottish continental shelf waters. 2006 was the second-warmest year in UK coastal waters since records began in 1870; seven of the 10 warmest years have occurred in the last decade. Recent warming is also evident in waters of the upper 1,000 m of the North Atlantic.	Climate change models indicate that SST will continue to rise in all waters around the UK coast, with stronger warming in the south-east (~0.15–0.4 ºC per decade in the southern North Sea) than the north-west (~0.05–0.2 ºC per decade at Rockall).
Storms and waves ERI	A greater incidence of severe winds and larger mean wave heights in western and northern UK waters are being observed.	Models predict overall fewer Atlantic depressions crossing to UK waters but there will be a greater number of deep depressions (intense storms) and associated increased wave heights.
Sea level Defra; MOHC; POL	Global average sea level has risen during the 20th century by between 1 and 2 mm per year. The latest published satellite measurements suggest the rise was around 3 mm per year between 1993 and 2003. Smaller rates of rise are seen in Scotland compared to the south of England. Extreme water levels have also increased in the UK, most likely as a consequence of mean sea-level rise.	During the 21st century a global average sea-level rise of between 9 and 88 cm relative to 1990 has been predicted but there is uncertainty in ice-melt and its effect on the upper limit of sea-level rise; thermal expansion will account for the majority of the overall rise. The anticipated range of relative sea-level rise by the 2080s (relative to the 1961–1990 mean) is 20–80 cm in south-west England and 0–60 cm in Scotland.
Acidification PML	The ocean is becoming more acidic as increasing atmospheric carbon dioxide (CO2) is absorbed at the sea surface. Models and measurements suggest that surface pH has decreased by 0.1 pH unit since 1750. The surface ocean has absorbed nearly half of the increased CO2 emissions due to burning of fossil fuels over the last 250 years, thus reducing the amount remaining in the atmosphere.	Continued acidification will reduce the ability of the ocean to take up CO2 from the atmosphere, which will have feedbacks to future climate change, further accelerating the accumulation of CO2 in the atmosphere. Future increases in ocean acidity will have major negative impacts on some shell/skeleton-forming organisms within this century.
Gulf Stream and Atlantic Heat Conveyor NOCS	The Atlantic Heat Conveyor (within which the Gulf Stream plays a role) helps to maintain relatively mild temperatures in north-west Europe. Some observations suggest that the Atlantic Heat Conveyor has reduced in strength by up to 30% since the early 1990s. More data are needed to distinguish this trend from natural variability, which has recently been shown to be large on a day-to-day basis.	It is very likely that the Atlantic Heat Conveyor will slow during this century, but not sufficiently to completely offset warming across the UK. There is considered to be less than a 10% chance of a collapse of the Atlantic Heat Conveyor this century.
Salinity FRS; IMGL; NOCS; SAMS	Surface waters to the north and west of the UK have become relatively more saline since the 1970s. There are no clear trends in the shallow coastal waters of the Irish Sea, southern North Sea and western Scotland. Deep waters of the North Atlantic have freshened over the past 40 years.	Climate-driven changes in precipitation, evaporation, ocean circulation and ice-melt might influence salinity.
Shelf sea stratification and the spring bloom Cefas; POL	There is evidence to suggest a recent trend towards stratification (layers of less dense water above more dense water) earlier in the year, resulting in earlier spring blooms of plankton – largely in response to warming air temperatures.	Changes to rainfall seasonality and extreme events may change stratification in areas of freshwater influence, such as estuaries. Stratification and spring blooms of plankton in our shelf seas will occur earlier in a warmer climate.
Coastal erosion Plymouth University	Coastal erosion is occurring along 17% of the UK coastline (30% of England’s coastline; 23% Wales; 20% Northern Ireland; 12% Scotland). Almost two-thirds of the intertidal profiles in England and Wales have steepened over the past 100 years. Steepening of the intertidal profile is particularly prevalent on coasts protected by hard engineering structures (this represents 46% of England’s coastline; 28% Wales; 20% Northern Ireland and 7% Scotland).	Both coastal erosion and steepening of intertidal profiles are expected to increase in the future, due to the effects of sea-level rise and changes to wave conditions.
Air–sea flux of heat and water NOCS	The exchange of heat and water between the ocean and the atmosphere plays an important role in driving the circulations of both the atmosphere and ocean. There is little evidence for major changes in air–sea fluxes of heat and water around the UK.	The global water cycle is likely to intensify but the effect of this change within the UK is uncertain.