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The annual
mean Central England Temperature has increased by about 0.5°C
during the 20th Century.
The 30-year mean of annual mean temperature in Northern Ireland
and Scotland increased by about 0.3°C from 1873 - 1902 to
1961 - 1990.
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The average number of storms in October to March
at UK
stations has increased significantly over the past 50 years.
However, the magnitude of storminess at the end of the 20th
century was
similar to that at the start.
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There is a tendency towards wetter
winters in north-east England and drier summers in south-east
England. There were no statistically
significant trends in precipitation in Northern Ireland for
the period from 1931-2000.
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Annual sea
surface temperature averaged around the UK coastline has increased
by about 0.5°C for
the period 1871 to 2000, with most coastal sites showing a
warming trend.
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Sea
surface salinity (SSS) averaged over the northern North Sea
from 1950 to 2002 shows decreasing salinity since the 1970s.
There is no discernible trend in mean SSS in the English Channel
from 1900 to the early 1980s. SSS averaged over the Irish Sea
from 1950 to 2002 shows a decrease in both winter and summer.
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There are local short-term variations in tide and surge levels
at UK sites but no long-term trends.
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After adjusting
for land movements, ‘absolute’ mean
sea level (MSL) around the UK coast has increased by about 1mm
per year during the 20th Century. ‘Relative’ MSL,
due to the combined effect of absolute MSL changes and land movements,
is increasing around most of the UK coast but remains constant
or is decreasing along some northern coasts.
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UK MSL shows
an increase in the rate of rise towards the second half of
the 19th Century but is now rising on average less fast,
i.e. there has been a decrease in the rate of rise in the 20th
Century. Trends in UK extreme sea levels match MSL trends closely.
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Wave data from ships and buoys indicate that the mean winter
wave height in the northeast Atlantic increased significantly
between the 1960s and 1980s. Satellite data confirm that this
increase continued into the early 1990s.
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In the northern
North Sea, there was an upward trend of about 5-10% (0.2-0.3m)
in mean significant wave height (Hs) for January–March
for the period 1973-1995, but a decrease thereafter. In the central
North Sea, the trend in Hs for January–March was upwards
until 1993/94, with a decrease thereafter. In the southern North
Sea, there is no discernible trend in Hs for January–March
from 1973 to date.
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At Sevenstones
LV, off Land’s End, the acceptable value
is an increase of 0.02 m/yr in mean wave height over a period
of about 25 years. This trend seems to have persisted into the
early 1990s at least, although recent winters have suggested
a levelling off.
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Two pulses of inflow into the North Sea in 1988/89 and 1998
coincided with unusually strong northward transport of anomalously
warm water through the Rockall Trough.
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Coastal flow conditions from the Irish Sea to Scottish coastal
waters changed considerably after 1977, with a further change
in Irish Sea outflow during 1980 to 1981, after which the flow
pattern returned to that of 1977-1980.
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The North Sea has both southerly and northerly offshore transport
of sediment. The nearshore sediment transport is predominantly
southerly on the N-S orientated sections and westerly on E-W
orientated sections.
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The English Channel has both westerly and easterly offshore
transport of sediment. The nearshore sediment transport is predominantly
easterly, with some reversals in the lee of headlands.
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The Celtic Sea has a variable offshore transport of sediment.
The nearshore sediment transport is predominantly northerly on
the N-S orientated coasts and easterly on E-W orientated coasts.
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The Irish Sea has southerly and south-westerly offshore transport
of sediment on the North Wales coast south of the Lleyn Peninsula
and northerly and north easterly offshore transport north of
the Lleyn Penisula (Bardsey Sound). The nearshore sediment transport
is predominantly northerly on the N-S orientated sections of
the coast and easterly on E-W orientated sections.
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Turbidity (water clarity) in the Menai Straits (Irish Sea)
deteriorated from the mid 1960s to the late 1980s. There was
no overall trend turbidity in the Irish Sea between 1987 and
1997
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Coastal changes in Scotland were mainly accretional during
the early and mid-nineteenth century. In most places accretion
rates fell and erosional conditions ensued around the turn
of the century but there was a general recovery to slight accretion
during the period 1920 to 1960. Between 1969 and 1981, approximately
40% of sandy beaches over 100m in length in Scotland were eroding,
22% were stable, 11% were advancing, 18% showed evidence of
both advance and retreat and 9% were protected or backed by
some other stable feature such as rocks.
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The northern coastline of Northern Ireland is principally
hard rock, so coastal erosion is minor and localized. The coast
to the west of the Bann River is an area of deposition. East
coast beaches are generally of late-Holocene age and are not
being renewed at a constant rate to match current sea-level rise,
with some consequent beach loss.
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In England, the largest erosion rates (i.e. greater than 1m/yr)
are along the east coast, with nearly 20% of the locations
in East England so categorised. Some 13 of the 18 locations
in North East England, where erosion exceed 1m/yr, fall along
the South Yorkshire coast. By comparison, less than 5% of locations
in all other regions have such high rates and this is particularly
noticeable in South West England and Wales.
