Environmental Engineering Reference
In-Depth Information
several months each year, a cold and arid atmosphere, more seasonal river regimes and a
subarctic ecosystem. Britons would be
true
Europeans, able to walk to mainland Europe
(with lower sea levels), which itself could not have been the birthplace of great
civilizations. This was the scene for most of the past 115 ka, since the last or
Eemian
temperate (interglacial) stage. Sea level was over 100 m lower than today and the North
Sea area was an extension of the north European plain. Permafrost and tundra conditions
prevailed, with intermittent episodes of Early Devensian mountain glaciation. A late
Devensian ice sheet, covering most of Britain and Scandinavia, coincided with world-
wide glaciation to drive sea levels down to - 130 m at 18 ka BP.
Thereafter, global warming and ice melt ushered in the Flandrian temperate stage.
Global sea levels were restored to 0-3 m above their present level by the Mid-Holocene
hypsithermal
or climatic optimum,
c
. 5 ka BP. Britain's continental shelf shrank
progressively and the coastline became far more indented. Orkney and Shetland became
islands at
c
. 13 ka BP and land bridges with Ireland and the outer Hebrides were drowned
by 12 ka BP. The Loch Lomond Stadial ice readvance checked further insularization until
after 10 ka BP, when the Inner Hebrides, Anglesey and the Isle of Wight were isolated.
The low coastal plain connecting the Thames-Rhine estuary as far north as Yorkshire and
Sussex-Flanders (northern France) was finally breached by the Flandrian transgression
c
.
8·5 ka BP, which completed the isolation of the British Isles (Figure 1).
Subsequent minor fluctuations may seem insignificant compared with the overall rise
of some 130 m. However, the last areas to flood - including the Wash, the inner Severn
estuary and the Solway Firth and Morecambe Bay fringe of Lancashire - became the first
areas reclaimed naturally during the minor regression (-1-4 m) which accompanied
cooling after 5 ka BP. Extensive peat formation in enclosed muddy estuaries, especially
the Somerset and Gwent levels (Severn estuary) and Fens (East Anglia), records their
subsequent environmental and human history. Similar minor climatic oscillations, such as
the
Medieval Warm Epoch
and
Little Ice Age
, between c. AD 800-1300 and AD 1350-
1850 respectively, caused major socioeconomic changes in Europe and altered sea level
by ±1-2 m. The extent and timing of changes were neither uniform nor synchronous -
just as forecast for the twenty-first century. Sea level first rose by about 1 m and then fell
by 1-2 m as European temperatures fluctuated by ± 1·5° C. These changes are small by
comparison with the Pleistocene-Holocene transition but were enough to create
substantial problems for coastline and hinterland management for our medieval ancestors.
This provides a warning for the twenty-first century.
