2 GLOBAL SYSTEMS: CLIMATE CHANGE, A CASE STUDYukscience.org/_Media/EG4310_Reader.pdf ·...

69EG4310 Sustainability and Global Systems Section 2

© MMU 2005

2 GLOBAL SYSTEMS: CLIMATE CHANGE, A CASE STUDY

2.1 Introduction

In the previous section you were introduced to the concepts of earth systems which

operate at global scales and what ‘global’ means in the context of sustainability. In this

section you will learn about the ideas and science behind global climate change.

Climate is a term used to describe average weather conditions and is therefore less

descriptive than weather. Climate defines and summarises a set of normal seasonal

weather conditions across the planet. Climate in the tropics is quite distinct from that

which we might experience in Europe or North America. The climate ‘system’ is a

holistic collection of separate processes and influences that may be defined as primarily

being atmospheric, oceanic, terrestrial, chemical and biological.

Like many complex stochastic systems the climate system is sensitive to a number of

conditions. Like a swinging pendulum, the world’s climate will always tend to want to

‘rest’ around a set of average states. Given some set of anomalous boundary conditions

(increased sea surface temperatures or raised air temperatures for example) and the

pendulum may swing more forcefully resulting in more unusual weather patterns in a

given year. The problem with climate change is that such anomalous events may become

the new ‘norm’ – allowing more extreme and hence devastating climate to dominate and

impact human society and natural systems.

Some opponents of climate change theory (and politics) say “so what if our climate

changes”? Surely we will develop new technologies to cope with this change! In fact this

argument is no different to asking every inhabitant of earth to jump off a cliff

proclaiming “don’t worry, some bright spark will tell us how to fly on the way down!”

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Every single aspect of human life is influenced by weather and climate. Agriculture,

health, leisure and tourism, transport policy, energy generation and consumption,

commercial and financial activities and hydrology are all directly affected. This means

that political institutions and nations take the threat of climate change across the globe

very seriously – not least the small island nations that are most vulnerable to sea-level

change. As key resources such as water, soil and vegetation become adversely affected

this will create great friction between nations possibly leading to conflict (Barnett, 2003).

While there are numerous academic institutions around the world studying the theory

and observations of global climate change, the overall responsibility of providing a

synthesis of known facts is borne by the UN Intergovernmental Panel for Climate

Change (IPCC). This group uses working parties of scientists to provide updated

synthesis reports dealing primarily with the scientific basis of climate change (Houghton

et al., 2001) and impacts, adaptation and vulnerability (McCarthy et al., 2001). Whilst there

are many individuals within the scientific community who oppose some of the published

material within the IPCC reports (sometimes due to political rather than scientific

rationale) it remains the single most uniform and consensus driven doctrine available.

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2.2 Evidence for past climate change

In order to understand the future state of any dynamic system we must try and observe

past behaviour of that system. We can derive evidence of past climate change operating

at a global scale by analysis of both physical proxies and dynamical models (Robinson

and Henderson-Sellers, 1999).

Firstly, we can say that the climate has changed in the past. What is debatable however is

the extent to which recent climate change is “unnatural” and due to human activity. Such

change might prove to be the start of an ever increasing temperature trend.

Figure 2.1: (a) Annual anomalies of global average land-surface air temperature (°C), 1861 to 2000, relative

to 1961 to 1990 values. Values are the simple average of the anomalies for the two hemispheres. The

smoothed curve was created using a 21-point binomial filter giving near decadal averages.

Source: IPCC (2001), Climate change 2001: The scientific basis.

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There are a variety of palaeoclimatic techniques used to determine how climate has

changed over long time periods. These climate reconstruction methods provide proxies of

past environmental conditions:

Tree Rings (dendroclimatology)

Each year of a tree’s life is recorded by the addition of a new growth ring around the

central trunk. The width of this ring is influenced by environmental conditions. In dry

climates ring width is affected by precipitation whereas in colder climates ring width may

be related to summer temperatures. See Frank and Esper, 2005.

Lake Sediments

During the course of an annual cycle (warm and wet followed by cold and dry), sediment

will often be deposited in a lake bed. These layers record the passing of time and contain

biological debris such as pollen and seeds from nearby vegetation and diatoms that have

lived in the water body itself. The temperature most favoured by specific tree/plant

species as well as coastal sea-level inundation can be inferred from these proxies. It is

common to use coring equipment to retrieve several metres of sediment for laboratory

analysis. See Ji et al., 2005

Pollen Analysis

As with lake sediments – pollen grains may be deposited over land and accumulate over

time. Using dating methods such as radiocarbon or caesium/americium markers the

proxy temperature conditions that were prevalent when the pollen was deposited can be

inferred. As with lake sediment analysis, material is often retrieved using coring

equipment. See Stebich et al., 2005

Ice cores

Changes in environmental temperature often leads to periods of snow (and hence ice)

accumulation as well as melting. If undisturbed ice core samples can be dated, the ice

may be chemically analysed and proxies derived from such variables. Oxygen isotope

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ratios can be used to determine temperature where sampled can be transported to

suitable laboratories. See Paul and Schäfer-Neth, 2005.

Other techniques such as loess deposits, deep-sea ocean cores, corals and palaeosols also

generate useful additional evidence for past climates.

In fact, the masses of evidence derived from such analysis has shown that our planet’s air

temperature has changed quite considerably over long time periods

Figure 2.2: Relative swings in temperature conditions inferred from a wide variety of proxies showing a

warm period (around 7kya) known as Holocene thermal maximum

(Source: ARIC http://www.doc.mmu.ac.uk/aric/gccsg/index.html)

Quantitative estimates of mid-Holocene warmth suggest that the Earth was perhaps 1 or

2°C warmer than today. Most of this warmth may primarily represent seasonal (summer)

warmth rather than year-round warmth. Beginning about 1450 A.D. there was a marked

return to colder conditions. This interval is often called the Little Ice Age, a term used to

describe an epoch of renewed glacial advance (see Figure 2.3).

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Figure 2.3: Indication of “little ice age” from temperature records.

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2.3 Causes of climate change

There are various competing influences that can be regarded as causally linked to

observable climate change. These can be partitioned into natural (internal and external

forcing) and anthropogenic (principally due to human industrialisation).

Natural external forcing is that which would influence our planet’s climate regardless of

human interference. The most important of these is orbital forcing – sometimes called

Milankovitch Cycles. Milutin Milankovitch (a Serbian astrophysicist) worked out ways in

which the Earth-Sun geometry changed as a function of orbital cycles (Liu, 1995, Pillans

et al., 1998 and Kukla and Gavin, 2004). The distance between the Earth and Sun

changes for a variety of reasons as does the quantity of solar energy reaching Earth.

The Earth follows an elliptical orbit around the Sun. Orbital stretch/shrink ~100,000 yrs

(see Figure 2.4). The three primary cycles are:

1. Variations in the Earth's orbital eccentricity—the shape of the orbit around the

sun.

2. Changes in obliquity—changes in the angle that Earth's axis makes with the

plane of Earth's orbit and

3. Precession—the change in the direction of the Earth's axis of rotation, i.e., the

axis of rotation behaves like the spin axis of a top that is winding down; hence it

traces a circle on the celestial sphere over a period of time.

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Figure 2.4: Milankovitch cycles (Source: University of Michigan, 2005)

http://www.globalchange.umich.edu/globalchange1/current/lectures/samson/climate_patterns/

As the quantity of solar radiation reaching the earth is also variable, we can summarise

this as solar cycles. There is really no such thing as a ‘solar constant’

We have already seen that orbital effects can change the quantity of solar radiation

reaching the Earth but the Sun generates variable quantities of energy due to its own

internal variability. Solar activity is known to have cycles – with a periodicity of about 11

years. As well as sunspot activity, the Sun can interact with our atmosphere by generating

solar flares leading to a powerful solar ‘storm’ (enhanced solar wind)

Solar flares can damage satellites, and can also affect the Van Allen belts producing

Aurora (Northern Lights).

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Primary sources of internal natural forcing include volcanic activity. Active volcanoes

generate large quantities of dust and smoke and particulates in the atmosphere block out

solar radiation, preventing it from penetrating through to the ground surface (Prothero,

2004). The main effects of volcanic eruptions are to cool the affected regions (not

dissimilar to a “nuclear winter”). When Mount Pinatubo erupted in the Philippines June

15, 1991, an estimated 20 million tons of sulphur dioxide and ash particles blasted more

than 12 miles (20 km) high into the atmosphere.

Whilst both internal and external natural forcing undoubtedly alters our climate over

varying time scales the most hotly debated and that which is likely to be most culpable is

anthropogenically induced forcing. The burning of fossil fuels is believed to be the major

source of anthropogenic climate forcing. Burning oil, gas and coal generates a wide

variety of gases and particulates – the most important of which is carbon dioxide (CO2).

The natural Greenhouse effect is enhanced by extra CO2 to create the Enhanced

Greenhouse Effect. Without the natural greenhouse effect global temperatures would be

around 253 K (-20ºC) but is actually 288 K (15 ºC). Other greenhouse trace gases include

Methane (CH4), Nitrous Oxide (N2O) and water vapour. What is typically referred to as

“the greenhouse effect” is really the enhancement absorption and re-emission of

outgoing longwave radiation (OLR) by increasing concentrations of the greenhouse

gasses. This process has been studied for several decades and has provided much debate

within the scientific community (Bard, 2004).

Human activity can affect the way in which the Earth surface responds to solar radiation.

Modifying land surfaces can profoundly affect heating and vulnerability to climate

change (Lioubimtseva et al., 2005). The gradual commercial deforestation of the tropical

rainforest regions in South America have removed a valuable carbon sink and released

carbon as this timber is burned or decays. The “slash and burn” policy attributed to

subsistence farmers in Africa and South America have removed tree species. Removal of

trees can lead to landslips, soil erosion and development of dust bowls. Changes in

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Sahelian grasslands (removal) may have modified the albedo and soil moisture regime

leading to droughts in the region.

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2.4 Scenarios and potential impacts of future climate change

Scenarios may be regarded as somewhat sophisticated ‘educated guesses’ achieved by

complex simulations dependent upon extremely powerful supercomputers.

Projections using the SRES (Special Report on Emissions Scenarios) emissions scenarios

in a range of climate models result in an increase in globally averaged surface temperature

of 1.4 to 5.8°C over the period 1990 to 2100 (Figure 2.5, IPCC, 2001).

Such a dramatic departure from existing temperature conditions will result in

unprecedented changes in climate and weather patterns. Key impacts include:

o Extreme weather events (frequency and magnitude)

o Human health (spread of diseases)

o Sea-level change (inundation of coastal areas and loss of island nations)

o Agriculture (loss of productive land leading to food security problems)

Read the IPCC (2001) report: Climate change 2001: impacts, adaptation and vulnerability

available from http://www.ipcc.ch.

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Figure 2.5: Variations of the Earth’s surface temperature: years 1000 to 2100. From year 1000 to year

1860 variations in average surface temperature of the Northern Hemisphere are shown reconstructed from

proxy data (tree rings, corals, ice cores, and historical records). The line shows the 50-year average, the grey

region the 95% confidence limit in the annual data. From years 1860 to 2000 are shown variations in

observations of globally and annually averaged surface temperature from the instrumental record; the line

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shows the decadal average. From years 2000 to 2100 projections of globally averaged surface temperature

are shown for the six illustrative SRES scenarios

and IS92a using a model with average climate sensitivity. The grey region marked “several models all SRES

envelope” shows the range of results from the full range of 35 SRES scenarios in addition to those from a

range of models with different climate sensitivities. The temperature scale is departure from the 1990

value.

Source: http://www.ipcc.ch/pub/un/syreng/spm.pdf

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2.5 Conclusions

The science and politics of global climate change is unique amongst global issues as the

consequences will be immense for humanity. It is unlikely that any section of human

society will escape the effects of climate change in the future.

As fossil fuels begin to become scarcer and fuel prices rise there will be a need for

alternative sources of energy. This will not happen any time soon though, and we may

already have reached a point of no return. Only by improving our understanding of the

science behind the problem can we tackle the issues in a rational and equitable way. For

this reason, the study of global climate change is a dynamic and contentious one and is

likely to remain so for some time.

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Reading and reflection 2.1

You should prepare briefing papers (four/five sides of A4) on

each of the following topics:

• Reconstructing past climate change – the science and methods used

• Climate change a new phenomenon? – Reconstructions of the last 15,000 years

• The science of climate change modelling – supercomputers and fundamental limits

• Scenarios of future global climate change

• The major impacts of potential future climate change


© MMU 2005

2.6 References

Bard E (2004). Greenhouse effect and ice ages: historical perspective. Comptes Rendus

Geosciences, Volume 336, Issues 7-8, Pages 603-638

Barnett J (2003). Security and climate change. Global Environmental Change, Volume

13, Issue 1, Pages 7-17

Frank D and Esper J (2005). Characterization and climate response patterns of a high-

elevation, multi-species tree-ring network in the European Alps. Dendrochronologia,

Volume 22, Issue 2, Pages 107-121

IPCC (2001). Climate change 2001: the scientific basis. Edited by Houghton J, Ding Y,

Griggs D, Noguer M, van der Linden P, Dai X, Maskell K and Johnson C. Published by

Cambridge University Press. ISBN: 0521 01495 6 and available online at

http://www.grida.no/climate/ipcc_tar/

IPCC (2001). Climate change 2001: impacts, adaptation and vulnerability. Edited by

McCarthy J, Canziani O, Leary N, Dokken D and White K. Published by Cambridge

University Press. ISBN: 0521 01500 6 and available online at

http://www.grida.no/climate/ipcc_tar/

Ji S, Xingqi L, Sumin W and Matsumoto R (2005). Palaeoclimatic changes in the Qinghai

Lake area during the last 18,000 years. Quaternary International, Volume 136, Issue 1, Pages

131-140

Kukla G and Gavin J Milankovitch climate reinforcements. Global and Planetary

Change, Volume 40, Issues 1-2, Pages 27-48

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Lioubimtseva E, Cole R, Adams J and Kapustin G (2005). Impacts of climate and land-

cover changes in arid lands of Central Asia. Journal of Arid Environments, Volume 62,

Issue 2, Pages 285-308

Liu H (1995). A new view on the driving mechanism of Milankovitch glaciation cycles.

Earth and Planetary Science Letters, Volume 131, Issues 1-2, Pages 17-26

Paul A and Schäfer-Neth C (2005). How to combine sparse proxy data and coupled

climate models. Quaternary Science Reviews, Volume 24, Issues 7-9, Pages 1095-1107

Pillans B, Chappell J and Naish T (1998). A review of the Milankovitch climatic beat:

template for Plio–Pleistocene sea-level changes and sequence stratigraphy. Sedimentary

Geology, Volume 122, Issues 1-4, Pages 5-21

Prothero D (2004). Did impacts, volcanic eruptions, or climate change affect mammalian

evolution? Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 214, Issue 3,

Pages 283-294

Robinson P and Henderson-Sellers A (1999). Contemporary climatology. Published by

Longman. Second edition. ISBN: 0 582 27631 4

Stebich M, Brüchmann C, Kulbe T and Negendank J (2005). Vegetation history, human

impact and climate change during the last 700 years recorded in annually laminated

sediments of Lac Pavin, France. Review of Palaeobotany and Palynology, Volume 133, Issues

1-2, Pages 115-133

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