Download how has climate change affected norfolk?

NORFOLK AND RECENT CLIMATE CHANGE
INTRODUCTION
You have probably read a lot in the press recently about climate change, and the
effect that changes in temperature and weather could have on our lives. As
Norfolk is relatively flat and low-lying, with an extensive coastline, it could bear
the brunt of any changes. Many present coastal areas are so low that they are
below estimated future sea levels. There is also the potential threat of
increased coastal erosion, and salt-water contamination of the region’s drinking
water and freshwater habitats such as The Broads.
Climate change is often portrayed as being a recent trend caused by human
activity producing lots of greenhouse gases and toppling the Earth’s natural
balance. Many recent scientific studies provide evidence to support this claim.
However, natural cycles of climate change, both warming and cooling, are known
to have taken place throughout the Earth’s history, over thousands of millions of
years.
Geologists divide up geological time into periods, with each period being partly
defined by a certain type of climate. Geological periods last for however long
the environmental conditions remain the ‘same’. The present geological period,
covers the last 2.6 million years of Earth history, and is called the Quaternary.
The Quaternary is quite different to other periods, as it defines the length of
time that the Earth has been experiencing a changeable climate with cycles of
warm and cold temperatures, with some cycles lasting longer, and having warmer
or colder temperatures, than others. Evidence shows that although there has
been a progressive long-term trend of global cooling during the Quaternary,
there have also been several different ice ages, or glaciations, separated by
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episodes of global warming where the climate was much warmer or more
temperate than the present day.
Norfolk hasn’t escaped these climate changes. In fact, the geological record of
the region, tells a story of episodes when temperatures were much warmer than
the present day, and the region resembled the ‘Costa del Cromer’! At other
times, the Norfolk landscape was covered by glacier ice and the climate would
probably have resembled that of present-day Iceland. These climatic changes
had a major effect on the local geography, influencing sea level and the position
of the coastline, the behaviour of rivers, as well as the existence of early
humans and flora and fauna.
HOW HAS CLIMATE CHANGE AFFECTED NORFOLK?
Today, Norfolk is situated on the western side of the North Sea. The North Sea
is shallow and Norfolk is relatively low lying. Unfortunately, Norfolk has no solid
high cliffs like the White Cliffs of Dover to keep the sea out! Consequently, it is
vulnerable to rising sea levels that may result from global warming. On the other
hand, during a cold episode, the world’s glaciers would grow; taking the water
that is presently in the seas. This could cause global sea level to fall by say
30 m. The North Sea would shrink in size, and Norfolk’s coast would move
northwards and eastwards. Norfolk would increase in size! But in contrast, a
30 m global sea level rise during a warm episode, when glaciers melt into the
seas, would cause the coastline in Norfolk to move westwards, swallowing up the
present day coastal areas.
To explain climate change during the Quaternary, it is helpful to divide it up into
two parts, the first, covering 2.6 million to 900,000 years ago, and the second,
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from 900,000 years to the present day. It is worth bearing in mind that the last
900,000 years is a short period of time, compared to the Earth’s total age of
4.6 billion years!
From 2.6 million to 900,000 years
Between about 2.6 million and 900,000 years ago, the coastline of ‘East Anglia’
lay much further inland (Figure 1). Southern England was joined to France, at the
Straits of Dover, which now links the North Sea to the English Channel. This
meant a ‘land-bridge’ existed between Britain and continental Europe, which
enabled animals to migrate between the two areas.
Figure 1 Geography of the United Kingdom and the North Sea Basin during the early Quaternary (c.
1,600,000 years ago) showing the position of the major rivers and coastline.
The climate is believed to have been mostly warmer than at present, with a
trend to slight cooling. Numerous small-scale oscillations from warmer to cooler
episodes occurred. The effect of these small climatic oscillations was to drive
frequent but relatively small falls and rises in sea level. In the Southern North
Sea area and Norfolk, this would have created a fluctuating coastline. In many
ways, the landscape would have looked very similar to parts of the present
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Norfolk coastline, with salt marshes, tidal creeks, mud and sand flats, river
estuaries, and pebbly beaches (Figure 2). In Norfolk, the sands, gravels and
muds that were laid down during this time, in this coastal environment, are
known as ‘crags’.
Figure 2 An ancient beach deposit at Norton
Subcourse in southern Norfolk. These sands
and gravels are called the Wroxham Crag.
Inland, Norfolk would have consisted of a low-lying vegetated coastal plain,
dissected by three major rivers that drained eastwards across central and
eastern England. Evidence of their existence is represented by extensive sand
and gravel deposits, which are exposed at the surface, or buried beneath
younger Quaternary deposits. The relatively stable climate, and the vegetated
land surface which protected the land from too much erosion, would have meant
that the rivers were relatively low energy, transporting mainly small grain
material such as sands, silts and clays through their catchments and into the
North Sea.
From 900,000 years ago to the present day
Around 900,000 years ago, a marked climatic shift occurred. The effects of
this move to a climate dominated by extremes have been marked, both globally
and locally.
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Over 20 major climatic shifts from ‘warm stages’, (or interglacials) to ‘cold
stages’, (or glacials), have been recognised globally within the last 900,000
years, each lasting several tens of thousands of years. Although evidence of only
some of these has been found in the UK, several of them have been identified in
East Anglia. Fossil plants and animals, such as beetles and small vertebrates,
suggest that the climate during many of these ‘warm stages’ was broadly similar
to that of the present day.
Also, on several separate occasions, the Norfolk region was located either near
the margins of, or buried beneath the British Ice Sheet that flowed southwards
from Scotland, and down the present coast of eastern England, into Norfolk.
During the maximum extent of glaciation, ice covered the whole of the British
Isles north of Bristol and London. The thickness of ice over Norfolk is
estimated to have been between 2 and 3 km.
How many glaciations there were is still unclear but at least three major
glaciations have been recognised: the earliest of these is called the Happisburgh
Glaciation and started around 640,000 years ago. The second, and largest
glaciation is called the Anglian Glaciation and occurred around 450,000 years
ago. The third glaciation, which didn’t extend as far into Norfolk, is known as
the Devensian glaciation which was at its coldest around 25,000 years ago.
Each of the glaciations dramatically modified the geography of Norfolk and
deposited vast quantities of sediment. Glaciers pick up material of all sizes as
they progress over the land, and carry it under the base of the ice. They smear
this onto the land surface as they travel over it, transforming the lie of the
land, or geomorphology. This material, which is generally very clayey, but can
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include all grain sizes, is called till, and it is this material that makes many of
Norfolk’s fields clayey (Figure 3). The water released from glaciers as they
melt, deposits huge amounts of sands and gravels as the glacier retreats. These
sands and gravels are also found in Norfolk, interbedded with the tills, and often
lie at the surface making some fields much sandier.
Figure 3 The cliffs at Happisburgh, north Norfolk, showing deposits laid down during the Happisburgh
Glaciation. Three layers of till are separated and overlain by sands that were deposited within a glacial lake.
Large changes in climate resulted in major changes in global sea level with sea
levels rising and falling between climatic episodes by several tens to hundreds of
metres, having a huge effect on the size and extent of the North Sea. During
periods of global warming, the position of the coastline may have been similar or
further ‘inland’ than at present. Shallow marine and coastal sediments (Figure 4)
above present sea level show that in the past, sea levels have been higher. In
contrast, in glacial stages sea level would have been much lower and the coastline
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would have lain considerably further to the east in the present offshore region
(Figure 5).
Figure 4 Rippled fine sands and
muds
at
Sidestrand,
north
Norfolk, deposited on an ancient
tidal flat.
Figure 5 The United Kingdom and
the North Sea Basin prior to
glaciation during the middle part
of the Quaternary (c. 800,000
years ago).
We know that climate change is a major driver of sea-level change. Likewise, the
activity of rivers also responded to the changeable regime. All of the rivers
began to transport higher quantities of material from further afield. The
glaciations eroded and buried the pre-glacial landscape, but due to post-glacial
erosion, much of the modern-day drainage network of Norfolk is superimposed
upon an ancient drainage pattern.
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DRIVERS OF GLOBAL CLIMATE CHANGE
1. The distribution of land and water
There are several theories to explain the glacial – interglacial cycles of the
Quaternary, but many scientists now believe that the distribution of the land
and water on the Earth’s surface is crucial. Because the oceans are linked this
allows large-scale flows of water between them. Land in the Earth’s mid and
high-latitude areas allows the growth of glaciers on them. This flow of heat and
moisture around the globe is called ‘thermohaline circulation’.
2. Solar Radiation
During the Quaternary, as well as this distribution of land and water, an
important driver of long-term climate change was temperature. Temperature is
controlled by the amount of solar radiation that we receive, which in turn is
controlled by our proximity to the sun. At longer time scales, typically thousands
to millions of years, the shape of the Earth’s orbit around the sun is known to
vary. Variations in the Earth’s orbit occur in cycles, and have the effect of
changing the amount of, and distribution of, solar radiation over the Earth’s
surface. These cycles are called Milankovitch Cycles after Milutin Milankovitch,
the Serbian astrophysicist who recognised them. He discovered three primary
cycles (Figure 1) listed below.
1. Orbital shape or eccentricity: The Earth’s orbit varies from being nearly
circular (called low eccentricity) to being slightly elliptical (high
eccentricity) over a 100,000-year cycle. During periods when the orbit is
elliptical, the Earth passes closer to the sun, and the amount of heat
received can be as much as 23% greater than when circular.
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2. Axial tilt or obliquity: The Earth’s spin can wobble between 22.1 and
24.5° over 41,000-year cycles, changing the tilt in the Earth’s axis. When
there is a large tilt, this makes winters colder and summers warmer.
3. Axial orientation or precession: The change in the direction of the
Earth’s axis of rotation relative to that of the sun over 21,000-year
cycles. When the distance to the sun is shorter and the Earth’s axis is
pointing towards the sun, one polar hemisphere will have warmer summers
and colder winters, whilst the other will be notably milder.
These orbital changes, combined with the distribution of land and sea, have
driven episodes of global warming and cooling. Over 100 such climatic changes
have been recognised, affecting global sea levels and the extent of the worlds
ice sheets and glaciers (Figure 2).
Global cooling events known as ‘cold stages’ or ‘glacials’, are indicated by the left
pointing peaks and labelled with even numbers. They are characterised by a
lowering of global sea level, as the water is being drawn away by the growth of
ice sheets and glaciers. Global warming events, called ‘warm stages’ or
‘interglacials’, are depicted with the right pointing peaks and odd numbers.
Interglacials are characterised by rising global sea levels, and the decay of ice
sheets and glaciers.
All figures featured are BGS  NERC 2006
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Figure 1 The Milankovitch theory of climate change, showing how changes in the Earth’s orbit around the
sun over long time periods affects the amount and distribution of heat over the Earth’s surface.
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Figure 2 Quaternary climate change. The left hand side of the diagram shows the global pattern of climate
change calibrated with a numerical and geomagnetic timescale. Evidence for known temperate, glacial and
periglacial climate episodes in East Anglia is shown. The controlling Milankovitch drivers are shown on the
right hand side of the figure.
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Discussion points / homework topics
1. The Industrial Revolution and climate change – what affect have humans
had on climate since the Industrial Revolution? How much of the climate
we are experiencing today is natural and how much is anthropogenic
(caused by man)?

Relevant books:
1) The Holocene – An Environmental History by Neil Roberts
2) The Great Ice Age – climate change and life by Wilson, Drury
& Chapman
3) Understanding Earth by Press, Siever, Grotzinger and Jordan
(Editor).
2. What other activities other than those discussed affect climate?
a. Volcanic eruptions – cause short-term variations in climate.
Enormous quantities of fine ash and dust released into the
atmosphere lead to localised reductions in temperature. As well as
this, the sulphur volatiles also released convert into sulphuric acid
in the atmosphere and results in cooling due to back scattering of
incoming long wave radiation, e.g. the Mount Pinatubo (Philippines)
eruption in 1991, when northern hemisphere temperatures dropped
by about 1oC.
b. Sunspots and solar winds – changes in radiative output from the
sun. Sunspots are dark areas of the Sun’s surface. Observations of
sunspot occurrence suggest that they have an eleven-year
periodicity. High levels of solar activity cause high solar winds,
which deflect cosmic rays.
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3. Research and summarise the findings of the two Greenland ice cores;
Greenland Ice Core Project, known as GRIP, (1989-1992) and Greenland
Ice Sheet Project 2, known as GISP2 (1989-1993). What were the main
results and what is the advantage of drilling two so close to each other?

References:
1) The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and
Our Future. Richard B. Alley (2002 Paperback).
This book is written by one of the leading scientists involved in the
interpretation of the GISP2 Ice Core. It is highly readable, accessible
and informative, explaining many of the main findings of GISP2.
Provides many more references that are useful when investigating Ice
Cores.
2) Dansgaard et al. (1993). Evidence of general instability of past climate
from a 250-kyr ice-core record. Nature 364, 218–220. This paper
outlines GRIPs main findings.
The advantage of drilling so close to each other, GRIP at the Greenland
Summit and GISP2 20km to the West, is the reproducibility of the
results. The two cores are identical for the last 110,000 years, making the
results and interpretations more reliable.
4. Many will assume the last 2.6 million years (The Quaternary) is a long
time, but in geological time it isn’t. The Quaternary is relatively short and
recent; try thinking of how short 2.6 million years is compared to 4.6
billion years using analogues, e.g. a roll of toilet paper represents 4.6
billion years, and the last 2.6 million years is represented by the last
2.6cm!
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Assumptions are as follows:

The toilet roll is 230 sheets long. The Which Report (Januray
2006) gives the number of sheets in various rolls. The average is
around 230 – 240

therefore a sheet represents: (4600 million divided by 230) 20
million years

assume that a sheet is 20 cm long (an easy number to work with but
probably an overestimate)

so 1 cm is 1 million years

so 2.6 cm is 2.6million years.
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