Download Climatology

Theme 7 – Climate Change
Read:
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Aguado & Burt: Chapter 16
Jeftic, Keckes, Pernetta – Climatic Change and the Mediterranean, Vols 1 and 2
We shall discuss climate change under the following headings:
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Past climates
Factors responsible for climate change
Methods used to estimate past climatic conditions
Application of GCMs to predict potential human effects (Global Circulation Model)
Defining Climate Change
It is far more difficult than originally perceived. Climate change is the norm not the unusual. Earth’s
climate is a complex system that responds to boundary conditions (external factors). Changes in
boundary conditions cause changes in the climatic system.
However it is believed that climatic systems may change even without corresponding changes in
boundary conditions – intransitivity. Another problem is associated with statistical interpretation of
measurements, ex: how does one establish a mean value? ie: over what time period?
Temporal and Spatial Changes
Is there global warming? The question is asked in terms of human time scale and rooted to the location
of the interlocutor. Oscillations that take place over longer time periods tend to have greater
magnitudes. Tropical latitudes tend to experience less severe climatic changes than higher latitudes.
Past Climates
The ‘normal’ climate for our planet is far warmer than it is at present; no permanent ice at all and sea
levels 150 – 200m higher than present. This illustrates the importance of seeing what span of time to
consider when calculating a mean global temperature. There were about 7 major ice ages in Earth’s
history all within 2.5 billion years (10-20% of the time). The latest Ice Age started about 15mya and is
still ongoing. Since there are still ice caps, we are considered to be in an Ice Age.
Pleistocene epoch: 1.8mya; known as the Ice Age
Holocene: covers the last 10,000 years and is often referred to as the time since the last Ice Age
These perceptions can be misleading since oscillations have occurred irregularly during the last 800,000
years.
From the time of the last interglacial, two main pulses of glaciations occurred – 125,000 years ago and
75,000 years ago. The peak of the last glacial episode dates back to 20,000 years ago – extensive ice
sheets covered continents while sea levels dropped by 120m.
What is clearly worrying is that Earth’s climate changes in an abrupt fashion. Climatic conditions switch
between cold and warmer conditions over a short period of time which allows little time for biological
and human adjustment.
Cave paintings found within the present Sahara desert testify to a thriving forest system as recently as a
few thousand years ago.
Factors in Climate Change
Including:
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Variations in solar output
Changes in Earth’s orbit
Variations in atmospheric turbidity
Changes in terrain characteristics and land configurations
Changes in present influences of ocean currents
Changes in radiation-absorbing gases
Variations in Solar Output
Solar Constant is somewhat misleading. There is a variation of 0.1% - 0.2% related to sunspot activity –
especially on the 10.7 year cycle. The Maunder Minimum (a period of greatly reduced sunspot activity
between 1645 – 1715) coincided with coldest period of Little Ice Age.
There is a quasi-biennial oscillation (QBO) which seems to have a more direct relationship. This involves
stratospheric winds over the tropics which change direction E-W or W-E in a two-year cycle. These shifts
affect surface atmospheric pressure with resultant Northern or Southern shifts in storm tracks. This is
an example of occurrences in the upper atmosphere affecting the lower atmosphere.
Changes in Earth’s orbit
There are three astronomical factors:
1. Eccentricity: Perihelion coincides with Northern hemisphere’s winter (Jan 4) and Earth is 3%
closer to the sun with a 7% increase in solar radiation – mitigates winter severity? 100,000 year
dominant cycle. This is because the Sun is not in the centre of the Earth’s orbit.
2. Precession: Orientation of Earth’s axis which, presently, points at the North Star, varies. If it
were to point at Vega, the Northern hemisphere’s winter would coincide with aphelion (further
away from the Sun) – more severe seasonal conditions. 27,000 year wobble.
3. Obliquity: The tilt of the Earth’s axis varies between 22.1 and 24.5 off the perpendicular (atm it
is 23.5). This has a huge effect on the seasons. 41,000 year dominant cycle. The last peak of
obliquity occurred 10,000 years ago.
These three cycles are referred to as Milankovitch Cycles.
Variations in Atmospheric Turbidity
Aerosols enter the atmosphere through volcanic emissions or human agency (smoke stacks/field
tilling/desertification etc) and can lodge at stratosphere and/or troposphere. These absorb solar
radiation and heat the atmosphere, reflect solar radiation and allow condensation of water droplets.
Changes in Terrain Characteristics
Reflective properties of the land surface have a direct bearing on climatic characteristics, including
albedo:
- Forest fires and deforestation
- Desertification
- Overgrazing
- Soil compaction and evapotranspiration
If glaciers melt, albedo decreases because of less ice surface to reflect sunlight, which causes more
glaciers to melt, etc – positive feedback.
Land Configuration
Effects of continentality and zones of maritime influence have changed with continental movements.
The Northern hemisphere’s land mass results in greater extremes of temperature, while the Southern
hemisphere has a greater maritime influence.
Changes in Ocean Currents
There is the so-called ‘great ocean conveyor belt’. Heat is released to the atmosphere in two locations
(near Canada and the North Pole), when water freezes to become ice it releases heat. If a point is
broken, for example if the water would not freeze, the ‘conveyor belt’ would collapse and another
system would arise to take its place.
Changes in Radiation-absorbing gases
The anthropogenic contribution of Carbon Dioxide. There is an exchange of Carbon Dioxide between
the atmosphere and the ocean, but an increase in water temperature results in release of Carbon
Dioxide  positive feedback. There are fast and slow processes in the Carbon cycle. The best way to
store Carbon is in coral reefs, where it is locked away as Calcium Carbonate. Because of global warming,
many coral reefs are dying away because the water temperature is increasing. It is better than forests,
because although forests take up Carbon Dioxide, if a forest fire occurs, it is all released back onto the
atmosphere.
Trace gases that contribute toward the anthropogenic greenhouse effect
- Carbon dioxide (50% contribution)
- CFCs (17% contribution)
- Methane (13% contribution)
- Dinitrogen oxide (7% contribution)
- Surface ozone (5% contribution)
- Water vapour is another very important factor, but is so unpredictable
Global Temperatures – Trend
Surface observations, over land and sea, build up a record of global average annual
temperatures since 1860. In the 1920s it fell, then it began to rise, plateaued for a while, then from the
1980s, began shooting up. These graphs prove that surface temperatures are increasing. Global
circulation models can be wrong because they make the wrong assumptions, or give more weight to
data which they shouldn’t. To test it, instead of taking it forward in time, send it backwards. Data
already exists of past temperatures, so exclude that data from the model, and see how the model has
performed compared to data that exists. Then, the model can be projected forward.
A “business as usual” plan is one that shows how temperature would change if we continued as
we are today, without making any changes.
Most people assume that global warming implies an overall shift to higher temperatures. In
several cases, changes would be in increased variance of temperature coupled with a mean shift. This
results in sudden, unpredictable weather phenomena.
Rainfall is also affected by global warming. In some models, the Mediterranean is predicted to
have more rain, in others it is predicted to get less or the same amount. What would probably happen is
that the drought period will be longer – this is already felt today.
Climate Change Impacts
- Unsustainable forestry
- Biodiversity loss
- Food supply and demand
- Land degradation
All these are linked. Land degradation will affect the food supply. In more extreme environments,
the food chains are simpler due to a reduced amount of organisms – the biodiversity is less, and there
are very simple, linear food chains. Simple food chains are often the most vulnerable to change.
It is predicted that in the 2080s there will be an increase in mixed forest and the reduction in
tropical rainforest.
Water stress is the amount of water needed to be able to get by. Using more than 20% of the
potential water resource is a problem. Malta uses 200%. Crop yields are also expected to change.
Wheat, maize and rice are the three staple crops of the world.
Sea level is rising at the moment and is expected to continue rising. Many cities are built near the
sea due to the use of ports. Just a few cm of water rise is enough to create lots of problems. With
storm surges, worse problems can arise.
Greenhouse Sceptics
Most dissension comes from fossil industry lobbyists but good arguments include:
o Most GCMs fail to account for water vapour fluxes
o CO2 may be less potent as a greenhouse gas than has been estimated
o Methane levels may actually be declining
o
Most GCMs tend to predict that more warming should have already taken place if they
are run back into the past. Now it is actually shown that there has been an
underestimation by GCMs, so this last point is no longer valid.
It is feared that a threshold may be reached and the rate of change will suddenly increase. The
system has not been studied for long enough for good predictions to be made. It is unknown what the
threshold would be. The situation can be likened to a titration, where just one drop is enough to
eventually make the chemical reaction occur.
Water vapour plays a crucial role
o Relative humidity rise by just 4% is equivalent, in terms of greenhouse effect, to a
doubling of CO2 content
o Temperature increase  greater evaporation  greater cloud cover  greater Earth
albedo  cooler surface temperatures (negative feedback)
Climate Politics
Framework Convention on Climate Change objective: to stabilize “greenhouse gas
concentrations at a level that would prevent dangerous anthropogenic interference with the climate
system”
Up to 1999, only Fiji had ratified the convention. But now, Russia’s latest signing is bringing the
Convention into force.
After much debate, Kyoto Protocol singed in 1997 set targets for CO2, methane and nitrous
oxides to 5% below 1990 levels by 2012. Individual countries’ contribution varied according to their pre1990 output. No specific penalty mechanisms for breach of the Protocol were agreed to. The USA
wanted target emissions to be traded, banked, and borrowed much like the Acid Rain Program.
The USA fears that adherence to greenhouse gas controls would render its products more
expensive and lose competitiveness. The EU and Japan are far more amenably to controls and backed
the Kyoto Protocol unilaterally. Russia has also recently joined. Developing countries, led by China,
want no controls on emissions to apply to them, claiming that it is not fair that they should control
development when most emissions were made by the west.
From 1st January 2005, the European Union initiated a Carbon trading exchange for its members.
This would force industry to factor carbon emissions into their production costs. The major objection to
this carbon exchange is the allocation system where industries are arbitrarily allocated a given number
of carbon emissions. Is the market (profit driven) a suitable framework for decision making with long
term effects? Estimates for current prices stand at 5-9 Euros per metric ton.
What are the costs of curbing CO2 emissions? These depend upon the possibility of trading
emissions between regions.
What are the costs of doing nothing? The organizations most interested in climate change are
insurance agencies. Consider the magnifying effect of a higher sea-level on future tsunamis – like the
latest Indian Ocean episode.
Engineering solutions:
o Pump CO2 into deep ocean sediment layers or deep coal seams
o Pump CO2 directly into oceans to stimulate algal blooms
Some estimates claim that adherence to Kyoto limits would only result in a reduction of 0.1 oF
from the expected 2.5oF rise by the year 2050. Mitigation measures include:
o Steady retreat from coastal development
o Development of resilient crop management practices
o Drought mitigation measures
o Flood protection systems
o Efficient fuel usage; etc
Types of adaptation to climate change could be anticipatory or reactive.
The IPCC 4th Assessment is now available of the PICC website.
Climate change is an integrated framework, it needs to be looked at as a whole.