1. Global Warming Seminar Why is the Earth the Temperature it is? Michael de Podesta November 2013

2. One problem… Do any of us have any personal evidence that the global climate is changing?

3. This Presentation… 1.Why is the Earth’s surface the temperature it is? 2.The Earth’s Atmosphere 3.Increasing Carbon Dioxide 4.Should we be concerned? 5.What’s going to happen? 6.What should we do?

4. Energy Balance

5. How hot does an object get when placed in front of a fire?

6. Light from the Sun heats the Earth… The Sun Earth 5400 ºC

7. Light from the Sun heats the Earth… Drawn to Scale… The Sun Earth (drawn 100 times too big) (drawn to scale)

8. Light from the Sun heats the Earth… The Earth then radiates heat away… Light from the Sun Earth

9. The Energy Balance of the Earth

10. Earth Warms Earth Cools Energy Balance: to scale World Energy Production heat input from the Sun heat lost from the Earth

11. Hold on a moment! What about all the heat rising up from the Earth’s hot centre?

12. Earth 6400 km radius 5500 ºC Heat flow is less than 0.1 Watt per square metre Temperature increases by ~20 ºC for each kilometre below the Earth’s surface Heat flow to and from surface from the Sun 240 Watt per Square metre

13. A remarkable fact… Heat flow from the centre of the Earth can be completely ignored when considering what determines the surface temperature of the Earth!

14. Some more details…

15. How much light reaches the Earth? Earth At the top of the atmosphere Above the Equator At midday About 1360 W/m 2

16. How much light reaches the Earth? Earth North Pole South Pole Equator 1360 W/m 2 680 Whole Earth Average 340 W/m 2

17. How much light reaches the Earth’s Surface Light reflected from Earth Average Value 100 watts per square metre Light from the Sun Average Value 340 watts per square metre

18. What determines the surface temperature of the Earth? Infra Red Radiation cools the Earth… Light from the Sun heats the Earth…

19. Radiation Balance Light from the Sun heats the Earth… Average Value 240 watts per square metre Average Value 240 watts per square metre

20. Radiation Balance How hot must the Earth be to radiate 240 W/m 2 ? Average Value 240 watts per square metre -18 ºC

21. A Question What is the average temperature of the Earth? 1 metre above the surface and averaged over: day and night, all latitudes and longitudes. all seasons (a) – 15 º C (b) – 5 º C (c) + 5 º C (d) + 15 ºC

22. Summary -18 ºC Average Surface Temperature 33 ºC Temperature for radiation balance +15 ºC Greenhouse Effect

23. The Earth’s surface is 33 ºC warmer than it would be if had no atmosphere

24. This Evening… 1.Why is the Earth’s surface the temperature it is? 2.The Earth’s Atmosphere 3.Increasing Carbon Dioxide 4.Should we be concerned? 5.What’s going to happen? 6.What should we do?

25. The composition of the atmosphere? Gas% Nitrogen (N 2 )78.1 Oxygen (O 2 )20.1 Argon (Ar)0.93 Water (H 2 O)0.1 to 1 Carbon Dioxide (CO 2 )0.039

26. Illustration of atmospheric composition About 100 molecules O2O2 Ar N2N2

27. Illustration of atmospheric composition About 1200 molecules Water(H 2 O)

28. Illustration of atmospheric composition About 10000 molecules Carbon dioxide (CO 2 )

29. Nitrogen (N 2 ), Oxygen (O 2 ) & Argon (Ar) Suppose the atmosphere contained no carbon dioxide or water N 2, O 2 and Ar is more than 99% of the atmosphere Molecules have one or two atoms Natural frequency of vibration in the ultra-violet Make atmosphere opaque to ultra-violet light Transparent to infra-red and visible radiation

30. Nitrogen (N 2 ), Oxygen (O 2 ) & Argon (Ar) With an atmosphere of only Nitrogen Oxygen & Argon, what would be the surface temperature? Average Value 240 watts per square metre Average Value 240 watts per square metre -18 ºC

31. Greenhouse warming is caused by Water (H 2 O) Carbon Dioxide (CO 2 )

32. What is special about H 2 O and CO 2 Molecules have three atoms Natural frequencies of vibration in the infra-red They make the atmosphere opaque to certain infra- red frequencies

33. Vibrations of CO 2 and H 2 0 Different types of molecular jiggling occur at different frequencies Water H 2 0 Carbon dioxide C0 2

34. The Transparency of the Atmosphere

35. Infra RedUltra VioletVisible Absorption bands

36. Infra Red Radiation cools the Earth…

37. Radiation Balance in the 20 th Century… On Average 240 W/m 2 On Average 390 W/m 2 150 W/m 2 sent back to Earth Average Value 240 W/m 2 On Average + 15 ºC

38. Greenhouse Warming 33 ºC Others <1 ºC CO 2 2 ºC H 2 O 31 ºC If H 2 O is a more important greenhouse gas than CO 2, why aren’t we worried about water vapour emissions?

39. Residence time Because excess H 2 O in the atmosphere causes rain within a few days Excess CO 2 in the atmosphere takes a few hundred years to remove Photo Credit http://www.cepolina.com If H 2 O is a more important greenhouse gas than CO 2, why aren’t we worried about water vapour emissions?

40. How the parts fit together Atmospheric Water Global Temperature Greenhouse Effect Evaporation Small slowly-changing contribution to Greenhouse Effect Carbon Dioxide Clouds

41. Greenhouse Effect Earth’s surface is warmed by the Greenhouse Effect Caused by: Water (mainly) and carbon dioxide Turns the Earth from a ‘snowball’ with a hot Equator into the relatively temperate place So what’s the problem?

42. This Evening… 1.Why is the Earth’s surface the temperature it is? 2.The Earth’s Atmosphere 3.Increasing Carbon Dioxide 4.Should we be concerned? 5.What’s going to happen? 6.What should we do?

43. Atmospheric CO 2 Concentration versus year Historical Value 280 ppm Current value ~395 ppm parts per million Click for latest value

44. Atmospheric CO 2 Concentration versus year

45. Carbon dioxide Why is the amount of carbon dioxide in the Earth’s atmosphere is increasing? We are digging up carbon as: Coal & Oil & Gas We are burning them! C+ O 2 →CO 2

46. My family’s CO 2 emissions 8500 kg of CO 2 per year at home 8000 kg For our holiday in California! 16.5 tonnes!! There are many families like Michael’s… Emissions of CO 2 are closely linked to many of the best things about ‘modern’ life

47. Carbon? Or Carbon dioxide? CO2O2 1 tonne of CO 2 0.27 tonne of C 0.73 tonne of O 2

48. Global CO 2 Emissions 30 billion tonnes CO 2 8 billion tonnes C EVERY YEAR

49. Question Is 8 billion tonnes of carbon per year (emitted as CO 2 ) a lot or a little?

50. Carbon Cycle (Amounts of carbon in billions of tons) 760 90 8 2,000 39,000 500 1,000 3,000 (Coal) 300 (Oil &Gas) 2 2 760 increasing at 4 per year 60

51. Cause for Concern? What is the effect of increased levels of carbon dioxide in the Earth’s atmosphere? Nobody knows

52. Radiation ‘Balance’ in 2012… On Average <240 W/m 2 On Average 390 W/m 2 150 W/m 2 sent back to Earth Average Value 240 W/m 2 On Average + 15 ºC +2 W/m 2 +?? ºC

53. Earth Warms Earth Cools Energy Balance: to scale heat input from the Sun heat lost from the Earth

54. Conclusions The surface temperature of the Earth is affected by the composition of the atmosphere. H 2 O is responsible for about 31 ºC of warming. CO 2 is responsible for about 2 ºC of warming. The concentration of CO 2 in the atmosphere is increasing due to human emissions. This will affect the energy balance of the Earth Warming is strongly expected. Many observations support the warming expectation. Pre-historic Correlations between CO 2 and Global Temperature Meteorological Temperature Estimates, Arctic Sea Ice Collapse

55. This Evening… 1.Why is the Earth’s surface the temperature it is? 2.The Earth’s Atmosphere 3.Increasing Carbon Dioxide 4.Should we be concerned? 5.What’s going to happen? 6.What should we do?

56. 4. Why are scientists are concerned 1.Pre-historic studies show a strong correlation between atmospheric CO 2 levels and global climate. 2.There are observed changes in climate

57. Prehistoric Studies ` 1 year of snow From approximately 16,250 years ago

58. Bubbles in Arctic and Antarctic Ice 300 ppm Maximum180 ppm Minimum Ice Ages 395 ppm

59. Cause for Concern? Observed Changes in Climate

60. A Question? One estimate of the Land Surface Temperature?

61. A Question? What has happened ? What did Global Warming Theory predict in 1981? http://berkeleyearth.org But its not just average temperature that matters

62. Arctic Sea Ice http://nsidc.org/arcticseaicenews/

63. Arctic Sea Ice Minima Daily Mail And now it’s global COOLING! Return of Arctic ice cap as it grows by 29% in a year 8 th September 2013 2012 2013

64. A Question Can we be completely sure that the climate changes we observe are caused by anthropogenic emissions of carbon dioxide? Man-made and Woman-made 2001: It is likely 2007: It is very likely 2013: It is very very likely

65. This Evening… 1.Why is the Earth’s surface the temperature it is? 2.The Earth’s Atmosphere 3.Increasing Carbon Dioxide 4.Should we be concerned? 5.What’s going to happen? 6.What should we do?

66. Climate Models ‘What’s going to happen?” Climate Models ‘add up’ the many factors Nobody knows

67. The best ‘realistic’ possibility… If we make a 50% cut in global emissions: 80% cut in the UK CO 2 concentraions will rise to twice historical levels and stabilise

68. IPCC Predictions… Global Mean Temperature We stop all emissions NOW We BEGIN to stop all emissions EVENTUALLY We BEGIN to stop all emissions NOW We do nothing

69. This Evening… 1.Why is the Earth’s surface the temperature it is? 2.The Earth’s Atmosphere 3.Increasing Carbon Dioxide 4.Should we be concerned? 5.What’s going to happen? 6.What should we do?

70. What should we do… NothingEverythingSomething

71. Unused Slides.

72. Contributions to Climate Forcing Greenhouse gases Carbon Dioxide Methane Chlorofluorocarbons Nitrous Oxide Ozone Aerosols Black Carbon Reflective aerosols Cloud droplet changes Land cover changes Sun Climate Forcing (W/m 2 ) 0+1

73. The spectrum of sunlight

74. IPCC Predictions… Climate Research Unit East Anglia University 2008 0.5 metres in 100 years ? 1 metre

75. IPCC Predictions… 1 metre in 100 years http://en.wikipedia.org/wiki/Sea_level_rise

76. UK CO 2 Emissions

77. Daily Rotation Northern Hemisphere Summer Northern Hemisphere Spring Equinox Northern Hemisphere Winter Northern Hemisphere Autumn Equinox Angle varies from 22.5º to 24.5º And back again every 40,000 years 23.5º tilt Earth Spins 365.25 times on its journey around the Sun

78. Carbon dioxide The amount of carbon dioxide in the Earth’s atmosphere is increasing… Historically280 ppm 1950310 ppm 2000365 ppm 2025about 425 ppm 2050450-550 ppm

79. Cause for Concern? Climate models

80. Climate Models What is the output of a climate model?

81. The Earth Orbits the Sun Daily Rotation Northern Hemisphere Summer Northern Hemisphere Winter Angle varies from 22.5º to 24.5º And back again every 40,000 years 23.5º tilt Earth Spins 365.25 times on its journey around the Sun

82. Most Southerly Advance Mid Winter Seasonal Changes in Ice Cover

83. Most Southerly Advance Mid Winter Most Northerly Retreat Mid Summer If summer day length increases by a minute or two or days are warmer on average by a small amount This area used to reflect 90% of sunlight Now it reflects only around 30% Warmer ground emits trapped CO 2 and Methane

84. Is 380 Parts per million a lot or a little? Camera Light 380 ppm ‘blue’

85. An additional 2 watts per square metre of ‘radiative forcing’ Scientific American March 2004