Climate Change: Impacts and Responses Topic 2: The Earth's
Climate System 1
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2 Image: NASA Earth Observatory Topic outline 1. Definitions 2.
Components of Earths climate system 3. Drivers of Earths climate
system (internal and external forcings and feedback mechanisms) 4.
Earth's energy balance and the greenhouse effect 5. Biogeochemical
cycles and links to the climate system
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3 Image Credit: Fred Kulpers Learning outcomes for this topic
Demonstrate an understanding of the main components of the Earths
climate system and how they interact Demonstrate an understanding
of what drives the Earths climate system Describe the Earths energy
balance and how it relates to the greenhouse effect Demonstrate an
understanding of how biogeochemical cycles influence Earths
climate
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4 Section 1: Definitions
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5 Earths climate system Radiative forcing Climate feedbacks
Outline: Definitions
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6 The climate system is defined by the dynamics and
interactions of its five major components: Atmosphere (air)
Hydrosphere (liquid water) Cryosphere (frozen water) Geosphere
(land surface) Biosphere (life) Climate system dynamics are driven
by both internal and external radiative forcings. Earths climate
system
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7 Radiative forcing relates to the amount of energy which Earth
receives from the sun, and how much Earth then radiates back into
space. Types of radiative forcing: external forcings are those
attributable to changes in the amount of energy that arrives at
Earth in the first place, internal forcings are all those factors
that determine how much energy is reflected or radiated by Earth.
Radiative forcing What can affect radiative forcing? changes to the
amount of incoming radiation changes to the amount of solar
radiation that is reflected away from the Earth, or changes in the
amount of energy that is radiated away from Earth.
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8 Fig FAQ8.1-1 (Chapter 8, IPCC AR5, 2013) Climate feedbacks
Feedbacks occur when an internal or external forcing results in
changes to the climate system which further impact climate system
dynamics in a feedback loop. A positive feedback operates to
increasingly impact climate. A negative feedback is self-limiting,
and offsets or reduces the prevailing change. An example of a
positive climate feedback is atmospheric water vapour.
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9 Section 2: Components of the Earth's climate system
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10 Components Interactions amongst components Outline:
Components of the Earths climate system
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11 Components of Earths climate system
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12 Image: www.noaa.gov Read more: The atmosphere The atmosphere
is mostly nitrogen (78.1%) and oxygen (20.9%), with trace gases
including argon and helium, as well as radiatively active
greenhouse gases such as carbon dioxide (0.035%) and ozone. The
atmosphere is made up of layers called the troposphere,
stratosphere, mesosphere and thermosphere, each with varying
temperatures and with different properties in terms of the gases
they contain.
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13 Schematic view of components of the climate system and its
interactions Image: IPCC 2007
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14 Section 3: Drivers of the Earths climate system
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15 Drivers of climate change External climate forcings Internal
climate forcings Feedbacks Outline: Drivers of the Earths climate
system
18 Image created by Robert A. Rohde / Global Warming Art Solar
variation Periodic and aperiodic fluctuations Solar variation and
volcanic activity account for some climate change within prehistory
Solar variations alone do not explain the currently observed
changes.
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19 Milankovitch cycles Eccentricity (a cycle of around 100,000
years) Tilt or Obliquity (a cycle of around 41,000 years)
Precession (a cycle of around 24,000 years) Image: Robert A.
Rhodes, Global Warming Art Schematic of the Earths orbital changes
(Milankovitch cycles) that drive the ice age cycles. T denotes
changes in the tilt (or obliquity) of the Earths axis, E denotes
changes in the eccentricity of the orbit (due to variations in the
minor axis of the ellipse), and P denotes precession, that is,
changes in the direction of the axis tilt at a given point of the
orbit. Source: Rahmstorf and Schellnhuber (2006).(IPCC 2007)
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20 Image: www.climate.nasa.gov Greenhouse gases Greenhouse
gases absorb and emit radiation within the thermal infrared range
Greenhouse gases include: water vapour, carbon dioxide, methane,
nitrous oxide, ozone, CFCs and others
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21 Image: www.nasa.gov Tropospheric aerosols Aerosols: Scatter
and absorb radiation, bringing about complex interactions with
climate Play a role in cloud formation Create positive and negative
forcing: Sulphate aerosols persist over time and reflect energy
from the sun resulting in cooling Black carbon particles settle on
Earth and reduce albedo which causes warming
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22 Image: www.nasa.gov Stratospheric ozone The ozone layer is
thinning due to effects of chlorine and bromine released from
manmade CFCs Holes have formed over the poles as a result of the
effects of seasonal stratospheric cloud formation Stratospheric
ozone has complex direct and indirect interactions with climate
Image of the largest Antarctic ozone hole ever recorded (September
2006), over the Southern pole
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23 Image: NOAA Ocean circulation changes
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24 Image: www.nasa.gov Land surface changes
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25 Image: NASA Volcanos A volcano is a rupture in the Earths
crust from which magma, ash and gases can escape. They have
far-reaching atmospheric effects.
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26 Fig SPM.5, IPCC AR5, 2013 Estimates of radiative forcing in
2011 relative to 1750
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IPCC 2014 Positive and negative feedback mechanisms 27
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28 Well-understood: Water vapour (positive feedback) Albedo
(positive feedback) Less-well understood: Land carbon cycle
(currently negative feedback) Clouds (positive and negative
feedback) Feedbacks not included in climate models: Methane
hydrates (positive feedbacks) Permafrost methane (positive
feedback) Our understanding of these feedbacks
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29 Section 4: Earths energy balance and the greenhouse
effect
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30 What is the greenhouse effect? Earths energy balance
Outline: Earths energy balance and the greenhouse effect
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31 What is the greenhouse effect? Image: www.nps.gov
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32 Earths energy budget Image: IPCC 2013 Global annual energy
flows are shown in Watts/m 2 TOA stands for Top of Atmosphere
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33 Section 5: Biogeochemical cycles and links to the climate
system
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34 What are biogeochemical cycles? The carbon cycle The
nitrogen cycle Outline: Biogeochemical cycles and links to the
climate system
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35 Transfer and transport of matter within the biosphere,
hydrosphere, geosphere and atmosphere Gaseous cycles (carbon,
nitrogen, oxygen, water) Sedimentary cycles (phosphorus, sulphur)
What are biogeochemical cycles?
38 Fig Box6.2, Chapter 6, IPCC AR5, 2013 The nitrogen cycle
Nitrogen is the most important element for plant growth Nitrogen
availability affects the rate of key eco-system processes Human
activities - fossil fuel combustion, the use of inorganic nitrogen
fertilizers, and release of nitrogen in wastewater have altered the
global Nitrogen cycle Box 6.2, Figure 1 | Anthropogenic reactive
nitrogen (Nr) creation rates (in TgN yr1) from fossil fuel burning
(orange line), cultivation- induced biological nitrogen fixation
(blue line), HaberBosch process (green line) and total creation
(red line). Source: Galloway et al. (2003), Galloway et al.
(2008).
40 Components of the climate system Radiative forcing External
forcings Internal forcings Climate feedbacks The greenhouse effect
Earths energy budget Biogeochemical cycles Summary
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41 IPCC Fourth Assessment Report: Climate Change 2007 (AR4)
available at www.ipcc.chwww.ipcc.ch IPCC Fifth Assessment Report:
Climate Change 2013 and 2014 (AR5) available at
www.ipcc.chwww.ipcc.ch Jansen, E., J. Overpeck, K.R. Briffa, J.-C.
Duplessy, F. Joos, V. Masson-Delmotte, D. Olago, B. Otto- Bliesner,
W.R. Peltier, S. Rahmstorf, R. Ramesh, D. Raynaud, D. Rind, O.
Solomina, R. Villalba and D. Zhang, 2007: Palaeoclimate. In:
Climate Change (2007). The Physical Science Basis. Contribution of
Working Group I to the Fourth Assessment Report of the
Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M.
Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L.
Miller (eds.)]. Cambridge University Press, Cambridge, United
Kingdom and New York, NY, USA. Rahmstorf, S., and H.J.
Schellnhuber, (2006). Der Klimawandel. Beck Verlag, Munich, 144 pp
Galloway, J. N., J. D. Aber, J. W. Erisman, S. P. Seitzinger, R. W.
Howarth, E. B. Cowling, and B. J. Cosby, )2003). The nitrogen
cascade. BioScience, 53, 341356. Galloway, J. N., et al., (2008).
Transformation of the nitrogen cycle: Recent trends, questions, and
potential solutions. Science, 320, 889. References
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42 End of Topic 2: The Earths Climate System Next Topic:
Climate Change in the Distant Past