1. Climate variability and climate change
Climate variability has been described as natural (long-term and linked with Ice Ages) and climate change has been described as the phenomena of a changing climate caused by humans. Climate change has also been referred to as the Anthropogenic Greenhouse Effect.
Page 1

2. But what is Climate and how is this different to weather?
Weather is the local physical properties of
Temperature
Air pressure
Humidity
Cloud cover
Wind
over relatively short periods of time.
Page 2

3. But what is Climate and how is this different to weather?
Climate is described as average temperature, precipitation and wind across large geographic regions over long periods of time.
The Climate System is the complex interaction between
the atmosphere,
the land (and its topography)
the oceans or other water bodies,
snow and ice
biota
Page 3

4. Climate variability – changes in climate from natural impacts
Climate is influenced by
Solar output
The earth’s rotation and spin (Milankovitch cycles)
The atmosphere
Ocean absorption
Ocean circulation (El Nino, Indian Ocean)
All of the above have contributed to past climate variability
Page 4

5. Climate variability Solar radiation provides the energy
The radiation balance is altered by a change in:
output or Earth’s orbit (Milankovitch cycles)
reflection – albedo
long wave radiation
Page 5

6. Milankovitch Cycles
Serbian mathematician Miltutin Milankovitch explained the changes in earth’s rotation and orbit around the sun
Milankovitch Cycles – Natural change in solar radiation striking the earth due to the gradual change over time of the earth’s orbit (eccentricity), the tilt of its axis (obliquity) and the direction of its axis (precession)
Page 6

7. Milankovitch Cycles Earth’s orbit (eccentricity) 100,000 year cycle
Tilt of earth’s axis (obliquity) 40,000 year cycle
The direction of its axis (precession) 26,000 year cycle

8. Milankovitch Cycles
The Milankovitch Cycles explain the variation in energy striking the earth but it is a complex system with many feedback systems and do not provide all the answers to why the climate varies.

9. Earths Energy Balance See the clip below for explanationIN
OUT
Energy from sun watts/m2
Energy lost to space
watts/m2
Energy Absorbed
Page 9

10. Climate variability CLIMATE VARIABILITY Solar output
Atmospheric composition
Ocean absorption
Ocean circulation
Rotation and spin
Page 10

11. Climate variability CLIMATE CHANGE Increased Greenhouse gases
Solar output
Atmospheric composition
Ocean absorption
Ocean circulation
long time frame
shorter time frame
Rotation and spin
Page 11

12. The Earth’s Energy Balance (Source: Australian Academy of Science, 2015, “The science of climate change: Questions and answers” p.7) Watch the clip below for an explanation.

13. Climate variability So climate variability is natural.
There is also natural greenhouse effect caused by the atmosphere of the earth.
The concentration of gases in the atmosphere is changing and this is the ‘Anthropocentric Greenhouse Effect’ and the cause of Climate Change.
Page 13

14. What is the greenhouse effect?
The greenhouse effect is a mechanism that keeps the earth some 35 degrees warmer than it would otherwise be.
It happens naturally because of particular gases in the air that absorb infrared radiation.
The main gases involved are water vapour, carbon dioxide and methane.
Page 14

15. Greenhouse Effect
The enhanced greenhouse effect or the anthropogenic greenhouse effect is that altered by human activities.
This change is caused by the increase in Greenhouse Gases.
This is basis of the observed current climate change.
Page 15

16. What is Climate Change?
Global climate change is a change in the earth’s climate including changes in:
temperature
precipitation
extreme weather events and
a rise in sea level
Page 16

17. What is meant by extreme weather?
Hot (cold) days & nights
Heavy rainfall events, hail & thunderstorms
Droughts
Floods
Tropical cyclones
Bushfires
Extreme winds
Page 17

18. Past climate records
Past climate records give clues about what to expect form increasing CO2 and methane in the atmosphere.
Ice age cycles initiated by variations in Earths orbit.
Changing temperatures triggered changes in the concentration of CO2 (and methane) in the atmosphere (melting ice and permafrost).
Receding ice sheets also reflect less sun.
These positive feedback effect amplify the initial disturbance.
Not that the changes in temperature lead the changes in CO2 (on following slide).
Page 18

19. Source: Australian Academy of Science, 2015, “The science of climate change: Questions and answers” p.9

20. How do we know about past climates?
Proxy data:
Tree-rings
Ocean sediments
Ice cores
Corals
Even patterns of past civilisations give us clues.
Page 20

21. What empirical evidence is there for climate change?
MGT3MCC MGT4MCC Page 21

22. Evidence for climate change (see Q3 in Australian Academy of Science, 2015, “The science of climate change: Questions and answers”)
The evidence for human induced climate change relates to:
Increasing greenhouse gas emissions from the burning of fossil fuels, cement manufacture and deforestation.
This has create an imbalance in that CO2 is added to the atmosphere faster than it is removed (in the biosphere and oceans)
This increase in atmospheric CO2 acts like a adding a blanket – warming the earth.
Page 22

23. Source: The Economist
Page 23

24. Source: Climate Change: The hottest year on record, The Economist, 21 January 2016

25. Source: The state of the planet, The Economist, 25 November 2015
Page 25

26. How has the atmosphere changed recently?
Carbon dioxide
180 ppm to 280 ppm – variation due to ice ages
260 ppm to 280 ppm - 10,000 years
280 ppm to 250 years ago
280 ppm to ppm* (45%) - since industrial revolution
*As at July mauna-loa-co2-data.html (Check the current CO2 level from this link)
Page 26

27. Where does atmospheric carbon dioxide come from?
Eating food (tied with respiration)
Glucose in food consumed
Water, heat and carbon dioxide released.
C6H12O O CO O
glucose oxygen carbon dioxide water heat
Page 27

28. Where does atmospheric carbon dioxide come from?
Fossil fuels burned (combustion)
stored energy released,
water, heat and carbon dioxide released.
Heat (Energy)
Light (Energy)
H2O
CO2
Page 28

29. Where can atmospheric carbon dioxide go?
Used by plants (where fossil fuels originate) , organic matter (soils), and sequestered in forests
Absorbed by oceans and marine organisms (can lead to acidification)
Sedimentary rocks
Page 29

30. The carbon cycle (Source: Australian Academy of Science, 2015, “The science of climate change: Questions and answers” p.13)
Page 30

31. The imbalance
The global carbon cycle (Figure 3.1) illustrates the imbalance of carbon accumulating in the atmosphere.
See also Figure 3.2 for accumulation of emissions from fossil fuels and land use change and that absorbed in the oceans and land (sinks)
Page 31

32. How do greenhouse gases warm the lower atmosphere ?
Earth’s surface absorbs solar radiation as the surface temperature increases and it emits infrared radiation
(recall the earth’s energy balance)
Greenhouse gases absorb infrared radiation
Water vapor, ozone, carbon dioxide, nitrous oxide, methane, chlorofluorocarbons (CFCs)
Page 32

33. Enhanced Greenhouse Effect
Greenhouse gases emit and absorb radiation (within the thermal infrared range)
Abundant greenhouse gases:
Water vapour (H2O)
Carbon dioxide (CO2)
Methane (CH4)
Nitrous oxide (NOx)
Ozone (O3)
CFCs
Page 33

34. Global warming potential
Greenhouse gases warm the Earth by absorbing energy and slowing the rate at which the energy escapes to space (acting like a blanket insulating the Earth). Different greenhouse gases can have different effects on the Earth's warming.
Their ability to absorb energy (their "radiative efficiency"), and
How long they stay in the atmosphere (also known as their "lifetime").
Page 34

35. Global warming potential
The Global Warming Potential (GWP) was developed to allow comparisons of the global warming impacts of different gases.
It measures of how much energy the emissions of one ton of a gas will absorb over a given period of time, relative to the emissions of one ton of carbon dioxide.
The larger the GWP, the more that a given gas warms the Earth compared to carbon dioxide over that time period.
Page 35

36. Global Warming Potential
Page 36

37. Climate change - warming
Climate change - warming arises from changes in the flows of energy through the climate system.
Increases in atmospheric GHG’s (long lived)
Increases in GHG’s (short lived)
Changes to land cover (replacement of darker forests with paler croplands) albedo
Increases in aerosols (cause cooling)
Solar fluctuations
Volcanic eruptions
See p.14 Australian Academy of Science, 2015, “The science of climate change: Questions and answers”
Page 37

38. Effect on Climate (Source: Australian Academy of Science, 2015, “The science of climate change: Questions and answers” p.14)

39. Climate warming
Human induced drivers are much larger than natural drivers as shown in Figure 3.4
Effects of volcanic eruptions are short lived
Solar variations small – and warming has continued to occur as solar activity decreases
See model simulations on p.15 (Figure 3.5) in the Australian Academy of Science, 2015, “The science of climate change: Questions and answers”, replicating human and natural influences on warming.
Page 39

40. Climate warming in the future
How much will the Earth warm in the future?
Depends, on the emission trajectory
Modelling into the future is highly uncertain so a number of scenarios are developed to help guide policymakers
Uncertainty also around feedback effects;
the impact of clouds
Ability of oceans to absorb carbon dioxide
Replacing trees with cropland
Page 40

41. Future climate change scenarios (Source: Australian Academy of Science, 2015, “The science of climate change: Questions and answers” p.16)