Climate change in the marine environment

iStock_2093966_HR_EDIT3 Photo:
© iStockphoto.com/AVTG

	WHAT IS ALREADY HAPPENING	WHAT COULD HAPPEN	CONFIDENCE
Temperature (air and sea) Find out more... NOCS, FRS, Met Office, UKCIP	Sea surface temperature (SST) and air temperature over the sea within the mid-latitude North Atlantic and UK coastal waters have been rising by 0.2 - 0.6 ºC per decade over the past 30 years. Warming is greatest within the English Channel and North Sea where temperatures have risen faster than land temperature. Warming is also evident in waters of the upper 1500 m of the North Atlantic.	Climate change models anticipate 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).	HIGH
Ocean salinity Find out more... NOCS, FRS, UKCIP, Cefas	An increasing trend in surface salinity since 1995 around the North Atlantic is less evident in the UK shelf-seas. Deep waters of the North Atlantic have freshened over the past 40 years.	Difficult to predict, but changes in precipitation, evaporation, ocean circulation and ice melt have the potential to impact upon salinity.	LOW
Storms and waves Find out more... NOCS, Met Office, ERI	There has been a greater incidence of severe winds and increasing wave heights (by about 2% per year) in western and northern UK territorial waters over the past 50 years.	Different modelling approaches project different scales of change but indicate that wind strengths and wave heights will increase.	HIGH (present) LOW (future)
Large-scale oceanic processes Find out more... NOCS	The Atlantic Meridional Overturning Circulation (MOC) helps to maintain relatively mild temperatures in north-west Europe. Some observations suggest that the MOC has reduced in strength by up to 30% since the early 1990s. However, other studies disagree with this interpretation.	Most climate models anticipate some reduction in strength of the MOC due to increased freshwater influence in high latitudes, but continue to show overall future warming of the UK climate. An abrupt MOC shutdown leading to rapid cooling remains a high-impact, low-probability event. Our level of understanding is hampered by both model and observation limitations.	LOW
Sea level Find out more... Hadley Centre, UKCIP	Global average sea level has risen during the 20th century by between 1 and 2 mm per year. Satellite measurements suggest the rise was around 3 mm per year between 1993 and 2003.	During the 21st century it is likely that global average sea level will rise by between 9 and 88 cm, relative to 1990, but will not be uniform around the world. The anticipated range of relative sea-level rise by the 2080s (relative to the 1961 - 1990 mean) is 20 to 80 cm in south-west England and 0 to 60 cm in Scotland.	MEDIUM
Acidification Find out more... PML	Ocean acidity has been relatively stable for over 20 million years. The ocean is becoming more acidic as increasing atmospheric carbon dioxide (CO2) is absorbed at the sea surface. Models suggest that surface pH has decreased by 0.1 pH unit since pre-industrial times.	Model projections suggest that the change in average pH in UK waters this century will exceed its current range of variation. The full impacts of acidification remain largely unknown but organisms such as corals, some plankton, shellfish and sea urchins are expected to become less able to produce calcareous parts, such as shells, by the middle of this century.	HIGH (for pH change)
Shelf-sea Stratification Find out more... Cefas	Stratification is the term used when the sea becomes layered due to changes in temperature and salinity with depth. The seasonal cycle of stratification in shelf-seas is subject to significant interannual variability in timing and strength. Modelling suggests that over the last 40 years, the timing of peak stratification in the Irish Sea has become later by about 20 days.	Possible changes in timing and strength of stratification. Changes to rainfall seasonality and extreme events may impact stratification in areas of freshwater influence, such as estuaries.	LOW
Seabed (nearshore and offshore) Find out more... Cefas	Unknown. At present there are no changes definitely attributable to climate change.	Changed sediment conditions at some coastal environments, such as partially enclosed lagoons and bar-built estuaries, may occur. Sediment supply may be altered if climate change results in the modification, construction or removal of sea-defences.	LOW

WHAT IS ALREADY HAPPENING

WHAT COULD HAPPEN

CONFIDENCE

Temperature (air and sea)

NOCS, FRS, Met Office, UKCIP

Sea surface temperature (SST) and air temperature over the sea within the mid-latitude North Atlantic and UK coastal waters have been rising by 0.2 - 0.6 ºC per decade over the past 30 years.

Warming is greatest within the English Channel and North Sea where temperatures have risen faster than land temperature.

Warming is also evident in waters of the upper 1500 m of the North Atlantic.

Climate change models anticipate 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).

HIGH

Ocean salinity

Find out more...

NOCS, FRS, UKCIP, Cefas

An increasing trend in surface salinity since 1995 around the North Atlantic is less evident in the UK shelf-seas.

Deep waters of the North Atlantic have freshened over the past 40 years.

Difficult to predict, but changes in precipitation, evaporation, ocean circulation and ice melt have the potential to impact upon salinity.

LOW

Storms and waves

Find out more...

NOCS, Met Office, ERI

There has been a greater incidence of severe winds and increasing wave heights (by about 2% per year) in western and northern UK territorial waters over the past 50 years.

Different modelling approaches project different scales of change but indicate that wind strengths and wave heights will increase.

HIGH

(present)

LOW

(future)

Large-scale oceanic processes

Find out more...

NOCS

The Atlantic Meridional Overturning Circulation (MOC) helps to maintain relatively mild temperatures in north-west Europe. Some observations suggest that the MOC has reduced in strength by up to 30% since the early 1990s. However, other studies disagree with this interpretation.

Most climate models anticipate some reduction in strength of the MOC due to increased freshwater influence in high latitudes, but continue to show overall future warming of the UK climate.

An abrupt MOC shutdown leading to rapid cooling remains a high-impact, low-probability event. Our level of understanding is hampered by both model and observation limitations.

LOW

Sea level

Find out more...

Hadley Centre, UKCIP

Global average sea level has risen during the 20th century by between 1 and 2 mm per year. Satellite measurements suggest the rise was around 3 mm per year between 1993 and 2003.

During the 21st century it is likely that global average sea level will rise by between 9 and 88 cm, relative to 1990, but will not be uniform around the world.

The anticipated range of relative sea-level rise by the 2080s (relative to the 1961 - 1990 mean) is 20 to 80 cm in south-west England and 0 to 60 cm in Scotland.

MEDIUM

Acidification

Find out more...

PML

Ocean acidity has been relatively stable for over 20 million years.

The ocean is becoming more acidic as increasing atmospheric carbon dioxide (CO2) is absorbed at the sea surface. Models suggest that surface pH has decreased by 0.1 pH unit since pre-industrial times.

Model projections suggest that the change in average pH in UK waters this century will exceed its current range of variation.

The full impacts of acidification remain largely unknown but organisms such as corals, some plankton, shellfish and sea urchins are expected to become less able to produce calcareous parts, such as shells, by the middle of this century.

HIGH

(for pH change)

Shelf-sea Stratification

Find out more...

Cefas

Stratification is the term used when the sea becomes layered due to changes in temperature and salinity with depth. The seasonal cycle of stratification in shelf-seas is subject to significant interannual variability in timing and strength.

Modelling suggests that over the last 40 years, the timing of peak stratification in the Irish Sea has become later by about 20 days.

Possible changes in timing and strength of stratification.

Changes to rainfall seasonality and extreme events may impact stratification in areas of freshwater influence, such as estuaries.

LOW

Seabed (nearshore and offshore)

Find out more...

Cefas

Unknown. At present there are no changes definitely attributable to climate change.

Changed sediment conditions at some coastal environments, such as partially enclosed lagoons and bar-built estuaries, may occur.

Sediment supply may be altered if climate change results in the modification, construction or removal of sea-defences.

LOW