Climate Change: Impacts and Responses Topic 2: The Earth's Climate System 1

2 Image: NASA Earth Observatory Topic outline 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

3 Image Credit: Fred Kulpers 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

4 Section 1: Definitions

5  Earth’s climate system  Radiative forcing  Climate feedbacks Outline: Definitions

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. Earth’s climate system

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.

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.

9 Section 2: Components of the Earth's climate system

10  Components  Interactions amongst components Outline: Components of the Earth’s climate system

11 Components of Earth’s climate system

12 Image: 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.

13 Schematic view of components of the climate system and its interactions Image: IPCC 2007

14 Section 3: Drivers of the Earth’s climate system

15  Drivers of climate change  External climate forcings  Internal climate forcings  Feedbacks Outline: Drivers of the Earth’s climate system

16 Drivers of climate change IPCC 2014

17 External Forcings:  Solar variation  Milankovitch cycles Internal Forcings:  Greenhouse gases  Tropospheric aerosols  Stratospheric ozone  Land surface changes  Ocean circulation changes  Volcanoes Climate forcings

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.

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 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)

20 Image: 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

21 Image: 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

22 Image: 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

23 Image: NOAA Ocean circulation changes

24 Image: Land surface changes

25 Image: NASA Volcanos A volcano is a rupture in the Earth’s crust from which magma, ash and gases can escape. They have far-reaching atmospheric effects.

26 Fig SPM.5, IPCC AR5, 2013 Estimates of radiative forcing in 2011 relative to 1750

IPCC 2014 Positive and negative feedback mechanisms 27

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

29 Section 4: Earth’s energy balance and the greenhouse effect

30  What is the greenhouse effect?  Earth’s energy balance Outline: Earth’s energy balance and the greenhouse effect

31 What is the greenhouse effect? Image:

32 Earth’s energy budget Image: IPCC 2013  Global annual energy flows are shown in Watts/m 2  TOA stands for Top of Atmosphere

33 Section 5: Biogeochemical cycles and links to the climate system

34  What are biogeochemical cycles?  The carbon cycle  The nitrogen cycle Outline: Biogeochemical cycles and links to the climate system

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?

36 The carbon cycle Fig FAQ6.2-1, Chapter 6, IPCC AR5, 2013

37 Read more: The carbon cycle Fig 6.1, Chapter 6, IPCC AR5, 2013

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 yr–1) from fossil fuel burning (orange line), cultivation- induced biological nitrogen fixation (blue line), Haber–Bosch process (green line) and total creation (red line). Source: Galloway et al. (2003), Galloway et al. (2008).

39 Fig Box 6.2-2; Chapter 6, IPCC AR Read more: The nitrogen cascade

40  Components of the climate system  Radiative forcing External forcings Internal forcings  Climate feedbacks  The greenhouse effect  Earth’s energy budget  Biogeochemical cycles Summary

41  IPCC Fourth Assessment Report: Climate Change 2007 (AR4) available at  IPCC Fifth Assessment Report: Climate Change 2013 and 2014 (AR5) available at  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, 341–356.  Galloway, J. N., et al., (2008). Transformation of the nitrogen cycle: Recent trends, questions, and potential solutions. Science, 320, 889. References

42 End of Topic 2: The Earth’s Climate System Next Topic: Climate Change in the Distant Past