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Climate Change:
Impacts and Responses
Topic 2:
The Earth's Climate System
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Topic outline
Image: NASA Earth Observatory
1.
Definitions
2.
Components of Earth’s
climate system
3.
Drivers of Earth’s 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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Learning outcomes for this topic
 Demonstrate an understanding
of the main components of the
Earth’s climate system and how
they interact
 Demonstrate an understanding
of what drives the Earth’s
climate system
 Describe the Earth’s energy
balance and how it relates to
the greenhouse effect
 Demonstrate an understanding
of how biogeochemical cycles
influence Earth’s climate
Image Credit: Fred Kulpers
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Section 1:
Definitions
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Outline:
Definitions
 Earth’s climate system
 Radiative forcing
 Climate feedbacks
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Earth’s climate system
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.
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Radiative forcing
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.
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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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.
Fig FAQ8.1-1 (Chapter 8, IPCC AR5, 2013)
An example of a positive climate feedback is
atmospheric water vapour.
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Section 2:
Components of the Earth's
climate system
Outline:
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Components of the Earth’s climate system
 Components
 Interactions amongst
components
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Components of Earth’s climate system
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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.
Image: www.noaa.gov
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Schematic view of components of the climate
system and its interactions
Image: IPCC 2007
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Section 3:
Drivers of the Earth’s climate
system
Outline:
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Drivers of the Earth’s climate system

Drivers of climate change

External climate forcings

Internal climate forcings

Feedbacks
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Drivers of climate change
IPCC 2014
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Climate forcings
External Forcings:

Solar variation

Milankovitch cycles
Internal Forcings:

Greenhouse gases

Tropospheric aerosols

Stratospheric ozone

Land surface changes

Ocean circulation changes

Volcanoes
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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.
Image created by Robert A. Rohde / Global Warming Art
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Milankovitch cycles
Schematic of the Earth’s orbital changes (Milankovitch cycles) that drive the ice age
cycles. ‘T’ denotes changes in the tilt (or obliquity) of the Earth’s 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)
Image: Robert A. Rhodes, Global Warming Art

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)
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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
Image: www.climate.nasa.gov
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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
Image: www.nasa.gov
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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: www.nasa.gov
Image of the largest Antarctic ozone hole
ever recorded (September 2006), over the
Southern pole
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Ocean circulation changes
Image: NOAA
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Land surface changes
Image: www.nasa.gov
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Volcanos
Image: NASA
A volcano is a rupture in the Earth’s crust from which magma, ash and
gases can escape.
They have far-reaching atmospheric effects.
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Estimates of radiative forcing in
2011 relative to 1750
Fig SPM.5, IPCC AR5, 2013
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Positive and negative feedback mechanisms
IPCC 2014
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Our understanding of these feedbacks

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)
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Section 4:
Earth’s energy balance and the
greenhouse effect
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Outline:
Earth’s energy balance and the greenhouse effect

What is the greenhouse effect?

Earth’s energy balance
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What is the greenhouse effect?
Image: www.nps.gov
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Earth’s energy budget

Global annual energy flows are shown in Watts/m2

TOA stands for Top of Atmosphere
Image: IPCC 2013
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Section 5:
Biogeochemical cycles and links to the
climate system
Outline:
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Biogeochemical cycles and links to the climate system

What are biogeochemical cycles?

The carbon cycle

The nitrogen cycle
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What are biogeochemical cycles?

Transfer and transport of matter within the biosphere,
hydrosphere, geosphere and atmosphere

Gaseous cycles (carbon, nitrogen, oxygen, water)

Sedimentary cycles (phosphorus, sulphur)
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The carbon cycle
Fig FAQ6.2-1, Chapter 6, IPCC AR5, 2013
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Read more: The carbon cycle
Fig 6.1, Chapter 6, IPCC AR5, 2013
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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
Fig Box6.2, Chapter 6, IPCC AR5, 2013
Box 6.2, Figure 1 | Anthropogenic reactive nitrogen (Nr) creation
rates (in TgN yr–1) from fossil fuel burning (orange line), cultivationinduced biological nitrogen fixation (blue line), Haber–Bosch
process (green line) and total creation (red line). Source:
Galloway et al. (2003), Galloway et al. (2008).
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Read more: The nitrogen cascade
Fig Box 6.2-2; Chapter 6, IPCC AR5 2013
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Summary

Components of the climate system

Radiative forcing
•
•
External forcings
Internal forcings

Climate feedbacks

The greenhouse effect

Earth’s energy budget

Biogeochemical cycles
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References

IPCC Fourth Assessment Report: Climate Change 2007 (AR4) available at www.ipcc.ch

IPCC Fifth Assessment Report: Climate Change 2013 and 2014 (AR5) available at www.ipcc.ch

Jansen, E., J. Overpeck, K.R. Briffa, J.-C. Duplessy, F. Joos, V. Masson-Delmotte, D. Olago, B. OttoBliesner, 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, 341–356.

Galloway, J. N., et al., (2008). Transformation of the nitrogen cycle: Recent trends, questions, and
potential solutions. Science, 320, 889.
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End of Topic 2:
The Earth’s Climate System
Next Topic:
Climate Change in the Distant
Past