Download Climate change 1.3

AS LEVEL GEOGRAPHY
G1: Changing Physical
Environments
Investigating climate change
1.3 What are the causes of climate
change.
Key Question 1.1 What are the world’s major climates and how do they relate to
biomes?
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The relationship between weather and climate.
An overview of the global patterns of climate.
An overview of biomes and their relationship with climate.
Key Question 1.2 What are the temporal patterns of climate change?
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Short-term climate change.
Long-term climate change.
Key Question 1.3 What are the causes of climate change?
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The evidence for climate change.
The atmospheric processes that result in climate change.
The relative role of environmental and human factors in recent climate
change.
Key Question 1.4 What are the issues resulting from climate change?
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Changing climates and shifting climatic belts and the effect on biomes.
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Increasing levels of extreme weather and the impacts on human activities.
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Rising sea levels and their impact on people.
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The variation of these impacts in different regions.
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The impacts of climate change on society.
Key Question 1.5 What strategies can be used to address climate change?
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Strategies to address climate change
(i)
at international level;
(ii)
by government action;
(iii)
by pressure groups and by individuals.
Key Question 1.6 How successful have strategies been in addressing climate change?
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Evaluation of attempts to reduce climate change.
The evidence for climate change
Information about ancient climates is
obtained from a variety of evidence that has
been influenced in someway by past
climates:
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Glaciological evidence
Geological evidence
Biological evidence
Historical and archaeological evidence
Glaciological evidence
•Glaciers
•Ice cores
•Isotope analysis
Glaciers
Whether glaciers are advancing or retreating is a
clear response to variations in climate.
The changes in the three main glaciers near
Chamonix in the French Alps have been studied.
These are the Mer de Glace, d’Argentierre and
des Bossons. Data suggests that there was a lag
of around ten years in the response of the
glaciers to any changes. It seems a small change
in temperature (0.5-1oC) over a period of 60-70
years is enough to cause glacial retreat.
Most glaciers in the northern hemisphere
showed a decrease in size in the twentieth
century. This may be a reflection of the general
rise in temperatures. However, some glaciers
such as the Hubbard glacier in Alaska have been
growing. This could be due to local conditions.
The Mer de Glace,
France
Glaciers
Changes in the positions of the Mer de Glace
Ice cores
Ice cores have been taken from the highest
parts of Greenland and Antarctica where
there is only a small annual loss of ice due
to melting. The cores span a time scale of
up to 18 000 years and are divided into
layers that represent one year’s
accumulation. Glaciologists analyse the
ice for chemical and radiochemical trace
elements. Microscopic air bubbles are
found in the ice. These can be used to give
us information about past atmospheric
pressure as well as gas content (e.g. CO2
and nitrous oxide). The quantity of acid
aerosols can be used to estimate the
frequency of past volcanic eruptions
(particles emitted from volcanoes have a
cooling effect on climate).
Glaciologist cutting
through an ice core
Isotope analysis
An isotope is one or more forms of an element that differ from
each other in atomic mass.
This technique involves studying the ratio between two oxygen
isotopes, 18O and 16O. In sea water, the ratio is 0.002 1:1.
During warmer times, more of the 16O isotope is evaporated,
leaving an excess of 18O. Ice cores can reveal a ratio in favour
of the heavier 18O isotopes in precipitation that fell during
colder periods in the past.
Geological evidence
•Carbon dating
•Sediment cores
Radio carbon dating
Radio carbon (C14) dating can be
used to determine the age of
fossils, rocks and sediments.
C14 is a radioactive isotope of
carbon that is taken in by plants
and animals. It has a half life of
5370 years. This means that only
half the C14 will remain in a
specimen that is 5370 years old.
Sediment cores
Sediment cores are extracted from lake beds ant the ocean
floor. The biological material in these cores can help us
understand how changes in the environment can affect life.
An example is the study of foraminifera (a type of plankton).
They are very sensitive to water temperature changes and so
their presence or absence from sediments indicates
fluctuations in climate.
Foraminifera
Geological evidence
We have to be careful when using geological
evidence for many reasons:
• Sometimes records are not complete
•Human activities have disturbed sediments and
soils
•Ice advances have changed / removed evidence
•Some sediments do not contain much organic
material.
Biological evidence
•Dendrochronology
•Pollen analysis
Dendrochronology
Dendron = tree
Chronos = time (Greek)
This involves studying the annual growth rings of trees. This growth is
dependent on the climate of an area. In semi-arid areas, the availability of
moisture influences annual growth (and therefore ring width). In boreal
(northern coniferous) forests, annual growth is influenced by
temperatures, (especially the influence of frost). As a tree gets older,
annual growth is spread over a wider circumference. However,
mathematical techniques can now compensate for this.
Cross-section through an
oak tree.
Pollen analysis
The characteristics of plants are influenced by climate. As climate
changes, so too the plant communities of an area.
Pollen preserved in peat and sediment can be used to reconstruct past
climatic conditions. The sediment layers (and therefore the pollen) can be
dated using radio carbon dating.
The frequency of different types of pollen indicates which types of species
were dominant at the time. To reconstruct the climate, we look at what
type of climate these species favour today.
A prepared slide of
pollen.
Historical and archaeological
evidence
•Printed material e.g.
weather diaries and records
kept by amateur
meteorologists.
•Paintings and engravings
e.g. cave paintings, paintings
from time of “Little Ice
Age”.
•Photographic material of
extreme events such as
floods and storm damage.
People skating on the
River Thames
The atmospheric processes that
result in climate change
The greenhouse effect
There is considerable misunderstanding over the terms
global warming and the greenhouse effect. Global
warming is usually viewed as a human problem. The
greenhouse effect occurs naturally and is produced by
certain gases in the atmosphere (the main ones being water
vapour and CO2). These gases absorb energy, help warm
the earth and maintain temperatures that enable life to
exist.
Short wave solar energy passes into the earth’s atmosphere.
Some wavelengths are absorbed, reflected or scattered.
The rest reaches the surface to warm the land ant the
oceans.
The greenhouse effect
The greenhouse effect
Because the earth’s surface is cooler than the sun, the earth
emits long-wave, largely infra-red energy back into the
atmosphere where much is absorbed by gases. Some can
escape and pass back into space. The absorbed energy
warms the troposphere and some is reflected back from
clouds. Some of this infra-red energy is in turn radiated
back to the earth’s surface, keeping it warmer than would
otherwise be the case. The remainder escapes into space.
The release of radiated long-wave energy is broadly in
balance with incoming solar energy and is often referred to
as the solar budget.
The greenhouse effect
Without the greenhouse effect and an atmosphere, the earth
would be like the moon. Here, temperatures rise to over
100oC when lit by the sun and drop to -150oC at night.
The average temperature near the surface of the earth
would be about -18oC instead of 15oC. While the system is
in balance, conditions remain suitable for life.
The atmospheric processes that
result in climate change
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The important questions here are:
Is there a link between the the increase in greenhouse gases
released into the atmosphere due to human activities and
any changes observed in the earth’s climate?
What evidence is there for change?
How much change is going to happen?
What effects will these changes have?
Can we (or are we willing to) act to stop these changes?
Is it already too late?
We will consider some of these issues in
this section and those that follow.
The relative role of
environmental and human factors
in recent climate change
• Environmental
- Solar activity
- Earth geometry and Milankovitch cycles
- Plate tectonics
- Ice-albedo effect
- Ocean circulations
- El Niño and La Niña
- Volcanic activity
Solar activity
One cause of climate change
might be changes in the
amount of energy emitted by
the sun. Measurements have
identified 11, 22, 100 and
79/80 year cycles. The 100
and 79-year cycles can be
combined to produce a 179
year cycle that scientists relate
to patterns detected in tree-ring
studies.
Earth geometry and Milankovitch
cycles
The earth’s geometry varies and this affects how much solar
energy is received by different parts of the earth. Milutin
Milankovitch (a Yugoslav scientist) calculated three ways in
which the earth’s geometry varies and these are called
Milankovitch cycles:
1
The earth’s orbit changes from being near-circular to
being more oval every 1 million years.
2
The earth wobbles on it’s axis every 40 000 years.
3
The axis of the earth moves around slowly every 20
000 years.
Earth geometry and Milankovitch
cycles
These cycles have been matched to the occurrence of ice
ages. However, there have been periods in the past (as long
as 250 million years) without glaciation. This suggests that
other factors are involved. The cycles will affect the
distribution of energy over the earth’s surface but barely
affect the actual amount of energy within the system. This is
seen as a criticism on the use of these cycles to define climate
change.
Earth
geometry and
Milankovitch
cycles
Plates are responsible for moving land
areas into different climatic regions,
but can plate movements actually
bring about climate change? There is
evidence that the existence of a land
mass at the poles (or surrounding
them) can encourage ice sheets to
develop. This may be due to the land
preventing warm ocean currents ( that
cause snowfall to melt) from reaching
the poles.
Research suggests that the formation
of the Himalayas and the Tibetan
plateau led to a cooling of the world’s
climate around 40 million years ago.
It has been suggested that without the
Himalayas and the Tibetan plateau,
the Indian monsoon would not
happen.
Plate tectonics
Ice-albedo effect
Albedo = The ability of a surface to reflect solar radiation.
Snow and ice can reflect huge amounts of incoming solar
energy (around 80 per cent compared to 25 per cent for
grass). A build up of snow and ice cover has a cooling
effect on the earth’s climate. Less snow and ice cover leads
to more heat being absorbed by the ground (and therefore a
warmer atmosphere).We must remember, however that
other factors, such as solar activity, can reverse this effect.
Ocean circulations and sea
surface temperatures
The oceans have their own circulations of warm and
cold water, an example being the Gulf Stream. There
are huge eddy currents in the oceans that are over
60km across. These can travel for hundreds of
kilometres before fading. These ocean circulations are
closely linked with atmospheric circulations.
The oceans receive about 80 per cent of solar energy.
Most of this is absorbed by the top 100m of water
therefore sea surface temperatures (SSTs) are
important in relation to global climate.
Ocean circulations and sea
surface temperatures
The Namias-Sabine hypothesis argues that sea surface
temperature anomalies (SSTAs) strongly influence
the atmosphere. They are believed to affect weather in
local and more distant locations (however, we do not
know to what extent). This link is known as
teleconnections. For example there is a link between
SSTAs in the equatorial Pacific and pressure patterns
over North America. Researchers are including SSTAs
in climate models to produce better long-term weather
forecasting.
Sea surface temperatures
Ocean circulations
Ocean circulations and sea
surface temperatures
Changes to the oceanic conveyor belt could have
dramatic effect on the whole world. Some researchers
suggest that there is a link between ice ages and the
global conveyor belt. Sudden changes may be due to
the breakdown of the conveyor belt. Global warming
may be the result of more freshwater being released
near the poles. This would make the North Atlantic
colder and cause the climate of Britain to become more
like that of Siberia. Understanding the links between
ocean and atmosphere may be vital if we are to be able
to predict future changes in climate.
El Niño and La Niña
El Niño
One clear example of the links between oceanic movements
and climate change concerns El Niño events. These occur in
the Pacific but disrupt the climate across much of the rest of
the world. El Niño means “boy child” and is so called
because its waters reach the Americas at about Christmas
time. El Niño Southern Oscillations (ENSOs) occur every
two to nine years. High sea surface temperatures in the
western Pacific trigger a reversal in the normal flow of the
Trade Winds and ocean currents that flow across the tropical
Pacific from the Americas towards Asia. Tropical rains
usually centred over Indonesia shift eastwards, influencing
wind patterns world-wide.
El Niño
Impacts include a stronger sub-tropical jet stream that has also changed
its position, shifting storm tracks and monsoons. These produce
unseasonable weather over many regions of the globe (through
teleconnections). Some success has been seen in the prediction of
ENSOs. The effects are proving hard to predict.
The impact
of an El
Niño
oscillation
E
l
N
i
ñ
o
La Niña
La Niña (“female child”) refers to an anomaly of
unusually cold sea surface temperatures in the
eastern tropical Pacific. They also occur at irregular
intervals (roughly half as often as El Niño) and are
therefore hard to predict. The effects of La Niña are
nearly the opposite to those of El Niño. The
western Pacific is warmer and wetter than usual but
the tropical eastern Pacific is colder and drier. In
the USA, the Pacific north west region is wetter
than normal but it is drier and warmer than normal
across much of the south. The impacts are most
clearly seen in winter at these latitudes.
Volcanic activity
Many eruptions since 1980 show clearly the
effects that volcanic eruptions can have on
climate change.
Mount St Helens
When Mount St Helens erupted on 18 May,
1980, it sent huge quantities of ash and
sulphate aerosol particles high into the
atmosphere. This had an effect on the earth’s
albedo causing more energy to be reflected.
However, the blast was mainly lateral and the
ash settled quickly. Because not much material
was sent into the stratosphere there was little
climatic disturbance. Computer estimates the
effect on annual average temperatures to be
less than 0.1oC for the northern hemisphere.
The effects of the eruption of
Mount St Helens.
Volcanic activity
Mount Pinatubo
In June 1991, the largest volcanic eruption for 80
years occurred in the Philippines. The magnitude
was estimated to be 10 times that of Mount St
Helens. According to the USGS, 5-8 km3 of ash
and aerosol particles were ejected into the
atmosphere. The cloud extended 24 km into the
stratosphere. In the following weeks, satellites
observed particles encircling the globe and
measurements confirmed that dust was shading part
of the earth. It has been estimated that average
global temperatures could be reduced by over 1oC
for up to five years. Volcanic eruptions seem to
have a cooling effect on the earth’s climate and
could contribute to glacial phases. The full cause
and effect. link between volcanic eruptions and
climate change is uncertain as other variables are
involved which may counteract the cooling effect.
Satellite image of
sulphur dioxide
cloud from eruption
of Pinatubo.
The relative role of
environmental and human factors
in recent climate change
• Human factors
- Changes in vegetation
- Pollution
Changes in vegetation
There are close links between vegetation and
climate. Variations in the distribution of
different plant species may be one indicator of
global warming.
Destruction of the world’s rainforests can
seriously disturb the balance between vegetation
and the atmosphere. Positive feedback can
result in semi-arid conditions and problems such
as soil erosion.
The boreal forests of the northern hemisphere
absorb more sunlight in winter than the snow
covered areas. The forests are therefore warmer
than the surrounding land and any change in the
vegetation cover could have climatic
consequences.
Boreal forest and
snow covered areas
in Alaska.
Pollution
The burning of fossil fuels and
deforestation have both resulted in a
steady rise in CO2 levels in the
atmosphere. There has also been an
increase in other gases which also
absorb outgoing energy from the
earth. This all has a warming effect
on the atmosphere.
Are any changes part of a long-term
trend or the result of human
activities?
The causes and consequences of
global warming are complex and the
subject of debate.
Pollution from a
chimney stack.