12
Global Warming and its possible impacts on Essex
What are the impacts of global warming?
We are already seeing biological change. Periodically there are articles in the newspapers recounting
the increased numbers of sharks seen off Cornwall or turtles off Scotland, but undoubtedly there is
much more significant change occurring on a more lowly scale. There arc many examples of plants
colonising Britain from southerly latitudes and for many previously coastal thermophiles to move
inland, such as the Mediterranean Bean Broomrape, Orobanche crenata, that has been at Cranham
since 1950 and which expands its seed bank ever hot summer. This is the only place in Britain where
it has persisted and is increasing. Other examples are the Buttonweed, Cotula, which has colonised
ponds in southern England, and the lettuce, Lactuca virosa, and the drought-resistant Hawkweed
Oxtongue, Picris hieracoioides, which formerly were found on warm chalk and coastal soil but are
now commonplace in Essex.
Study of such change is known as phenology and has been the subject of articles in the last two
issues of the Club's newsletter and of an article later in this Naturalist by Sparks, Roy and Mason.
The role of Recorders in supplying the basic information for such studies is paramount.
The patterns of climate change indicate that Britain is becoming warmer (Fig. 5), with drier summers
and wetter winters (Fig. 6). Forecasts suggest we could have a climate akin to that experienced in
the south of France today. This could have immense impacts on farming. Obviously the crops we
grow in Britain, in Essex, are basically not suited to hotter drier summers. Different strains or even
completely different crops will have to be grown, for instance maize might become more
commonplace. Farming methods will have to change also. The trend towards larger fields and
arable farming make the land more vulnerable to soil erosion. This is not a problem in Essex at the
moment, though it does occur, even on heavier soils such as on the till (boulder clay) near Toot Hill,
to the southwest of Ongar. With increased amounts of rainfall in the autumn and winter, when many
fields are bare, erosion will become more frequent. Soil erosion is more likely on light soils and on
longer slopes that are bare or poorly vegetated during periods of heavier rain. The current practice
of autumn ploughing in larger fields would leave soils vulnerable to the winter rains. However,
ploughing patterns can be changed and field sizes decreased.
Sea-level rise is predicted. This partly due to the slow subsidence of the land in southeast England,
but a more important element is an absolute rise in sea level as global warming causes the polar ice
caps to melt. However, sea level has been oscillating for at least the last two thousand years, so
whether this rise is humanly induced or natural is open to debate. Whatever the outcome of the
debate, the rise is real. Salt marshes are already in decline around Essex (plate 1), with losses of up
to 44% (along the Stour) between 1973 and 1988. Under natural conditions these marshes would
migrate as sea level rises or falls. With the current rise of sea level, the marshes should be migrating
inland, but the sea-walls and other defences are preventing this. Another impact is that coastal
installations or properties will become vulnerable. In some cases the response is to give the land
back to the sea, as at Tollesbury, as long-term protection would be expensive and not necessarily
successful. In other cases, the coast has to be defended. Perhaps the most obvious cases in Essex
are the oil installation at Copperas Bay, Parkeston (plate 2), where shingle defences are being set up,
and east London, now protected by the Thames Barrier and satellite barriers on the Lea and Roding.
The increased temperature will mean more robust meteorological conditions. At least two or three
of the hurricanes affecting Florida and the southeast United States reach Britain each year. These
usually arrive in a form little or no different from the usual depressions that pass over Britain,
though, every two years or so one is still vigorous enough to rattle windows. These degraded hurricanes
Essex Naturalist (New Series) 17 (2000)