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Climate of the marine environment

WavesOcean 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.

Where headline messages under each topic are new for 2010-2011, they are highlighted in bold text. Arrows show change in confidence since the 2007-2008 MCCIP Annual Report Card. Where a topic is referred to in the 'regional snapshot' map, a map symbol appears.

  WHAT IS ALREADY HAPPENINGWHAT COULD HAPPEN

Temperature (Air and Sea)

Marine Scotland; NOC; Cefas; IMGL; MOHC; PML; SAMS

Same confidence High Confidence   Regional SnapshotLess confidence Medium Confidence   Regional Snapshot
  • Marine air and sea surface temperatures have risen over the north-east Atlantic and UK waters in the last 25 years.
  • The largest increase in air temperature has been over the southern North Sea at a rate of around 0.6°C per decade.
  • The largest increases in sea surface temperature have occurred in the eastern English Channel and the southern North Sea at a rate of between 0.6 and 0.8°C per decade.
  • Although temperatures are generally increasing, inter-annual variability is high. 2008 UK coastal sea surface temperatures were lower than the 2003-2007 mean.
  • Models project that temperatures will continue to rise in UK and north-eastern Atlantic waters up until at least the 2080s. However, in the next 10 years, natural oceanic and atmospheric variability make it difficult to predict whether temperatures will go up or down.

Storms and Waves

ERI; NOC

Less confidence Medium Confidence   Same confidence Low Confidence  
  • Natural variability in wave climate is large and the role of anthropogenic influence is unclear.
  • Increases in monthly mean and maximum wave height in the north-eastern Atlantic occurred between 1960 and 1990; however, this rise in wave height may be part of long-term natural variability. There has been no clear pattern since 1990.
  • There is no consensus on the future storm and wave climate for north-western Europe, since projected future storm track behaviour varies among atmospheric models.
  • Predictions of storm behaviour used by the UKCP09 wave model show storm tracks moving south, resulting in lower wave heights to the north of the UK and slightly larger wave heights in some southern regions, especially the south-west.

Sea Level

NOC; MOHC

Same confidence High Confidence   More confidence Medium Confidence   Regional Snapshot
  • Global sea level has risen at a mean rate of 1.8mm per year since 1955. From 1992 onwards a higher mean rate of 3mm per year has been observed.
  • Sea-level rise measured over the UK is consistent with the observed global mean
  • Projections of change in the UK suggest a rise of between 12 and 76cm by 2095, compared to a 1980-1999 baseline. This
    approximately equates to rates of between 1.2 and 7.6 mm per year respectively.
  • Considering projected land movements, a greater rise in southern regions of the UK is likely relative to the north.

Ocean Acidification

PML; Bristol University; MBA

Same confidence High Confidence   Same confidence Medium Confidence  
  • The ocean is becoming more acidic as increasing amounts of atmospheric carbon dioxide (CO2) are absorbed at the sea surface. Models and measurements suggest about a 30% decrease in surface pH (an increase in acidity) and a 16% decrease in carbonate ion concentrations since 1750.
  • The rate of change in pH is faster than anything experienced in the last 55 million years and is causing concern for marine ecosystems and species.
  • Oceans will continue to acidify with increasing CO2 emissions.
  • Whilst we have high confidence that ocean acidification will continue, subsequent impacts on ecosystems are less well understood.
  • Future increases in ocean acidity may have major negative impacts on some shell and skeleton-forming organisms by 2100.

Atlantic Heat Conveyor

NOC; Cefas; MOHC; Reading University

More confidence Medium Confidence   More confidence Medium Confidence  
  • Daily observations of the Atlantic heat conveyor began in 2004, revealing substantial daily to seasonal variability. At present the record length is too short to determine inter-annual variability or longer-term trends.
  • Observations and ocean models provide some evidence for recent slowing at some latitudes, during the 1990s and early 2000s. However, we do not yet have compelling evidence for a direct influence of changes in the Atlantic heat conveyor on climate in and around the North Atlantic over recent decades.
  • It is very likely that the Atlantic heat conveyor will slow this century, with models predicting an average 25% reduction of pre-industrial strength.

Salinity

Marine Scotland; Cefas; IMGL; NOC; PML; SAMS

Same confidence Medium Confidence   Regional SnapshotSame confidence Low Confidence  
  • The shelf sea and oceanic 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 shelf sea waters of the Irish Sea, southern North Sea and western Scotland.
  • Salinity of the deep waters of the North Atlantic decreased between 1960-2000 but has been stable for the last decade.
  • The salinity of shelf seas and oceanic surface waters may decrease slightly, though there are considerable uncertainties due to the influence of climate-driven changes in precipitation, evaporation, ocean circulation and ice-melt.

Shelf Sea Stratification

NOC; Cefas

Same confidence Medium Confidence   Same confidence Low Confidence   Regional Snapshot
  • There is some evidence that temperature stratification over the north-western European shelf seas is beginning slightly earlier in the year.
  • There is no suggestion of strengthening of stratification beyond the normal inter-annual variability.
  • Models project that by 2100 thermal stratification will begin around seven days earlier and end five to ten days later, decreasing the period of vertical shelf sea mixing. 
  • The strength of stratification in north-western European Shelf Seas could increase in response to changes in seasonal heating and rainfall.
  • Changes to stratification of coastal waters caused by inputs of fresh water (from changes in rainfall) cannot yet be predicted by existing models.

Coastal Erosion

Univeristy of Plymouth

Same confidence High Confidence   Regional SnapshotSame confidence Low Confidence  
  • Coastal erosion is a complex process that has a variety of causes, with rising sea level being only one of them. Whereas climate change and relative sea-level rise are global and regional phenomena, respectively, coastal erosion is a local process.
  • Currently, around 17% of the UK coastline experiences erosion (30% of the coastline in England; 23% in Wales; 20% in Northern Ireland; 12% in Scotland).
  • Where the coast is protected by engineering structures (46% of England's coastline; 28% Wales'; 20% Northern Ireland's and 7% of Scotland's is protected by artificial structures), steepening of the intertidal profile and a narrowing of the intertidal zone resulting from rising sea levels commonly occurs.
  • 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 Exchanges of CO2

PML; Cefas; UEA

NEW
Low Confidence  
NEW
Low Confidence  
  • The ocean removes about one quarter of atmospheric CO2 emissions from human activity.
  • Some areas of the ocean absorb more CO2 than others; some areas release CO2 back to the atmosphere.
  • The north-west European shelf seas are thought to be an area of CO2 uptake.
  • The efficiency of CO2 uptake by some areas of the ocean, including the north-east Atlantic, may be decreasing.
  • Increases in atmospheric CO2 will drive an increase in the CO2 content of the surface waters of the ocean. This is expected to increase the partial pressure of CO2 to double its pre-industrial level by 2050.
  • The proportion of CO2 from anthropogenic emissions taken up by surface waters may decrease as sea surface temperature rises (reducing solubility) and CO2 content increases (reducing buffering capacity). Other processes that affect CO2 uptake are less well understood (e.g. stratification, upwelling, ocean circulation and primary production).

Air-sea Exchanges of Heat and Water

NOC

Same confidence Low Confidence   Same confidence Low Confidence  
  • The exchanges of heat and water between the ocean and the atmosphere play an important role in driving variability in the circulations of both the atmosphere and the ocean.
  • An increase in ocean heat content has been identified, both globally and for the North Atlantic since 1960 (with an estimated upper limit of about 0.5 watts per square metre).
  • Obtaining reliable predictions of future changes in the air-sea heat and freshwater fluxes in the UK marine environment is difficult as the anthropogenic signal is small and may be strongly influenced by changes due to natural variability in the climate system.