Climate Change and its consequences Bill Menke October 4, 2005

1. Climate Change and its consequences Bill Menke October 4, 2005

2. Summary • The factors that influence global temperature • The role of greenhouse gasses • Anthropogenic emissions of greenhouse gasses • Natural Variability and Modeling efforts • Hazards of increased temperatures

3. 343 W/m2 Sunlight – mostly visible light Maximum = 1370 W/m2 Average* = 1370 / 4 = 343 W/m2 Aboput 30% reflected as visible light The rest converted absorbed by earth Earth’s surface gets hot and re-radiated energy as Invisible Infrared radiation 240 W/m2 103 W/m2 *average: surface area of earth is 4pr2, but only a disk of diameter pr2 faces the sun, hence the average is one fourth of the maximum

4. 1370 Watts 1370 W/m2 One toaster per square meter that’s a lot of heat … 1 square meter

5. E = c T4 With T in Kelvin and c = 5.6 x 10-8 W/m2K4 Infrared energy radiated by a hot object depends strongly upon it temperature 1 square meter temperature, T

6. 240 Watts downward Balanced by 240 Watts upward 240 = 5.6 x 10-8 T4 So how hot is the earth’s surface T = ( 240 / 5.6 x 10-8 )1/4 = 255 K = -17 deg C = 1 deg F 1 square meter temperature, T

7. Reality Check ! 255 K is too cold We must be doing something wrong ... New style of summer clothing

8. We forgot the Atmosphere Layer just thick enough to absorb all Infrared radiation that shines upon it

9. Energy balance: IR shining into a layer Must be balanced by energy radiated by layer

10. Sun 240 down Top surface 240 up T0 = 255K Model with two layer atmosphere Top of Atmosphere upward radiation must balance solar input cT04 = 240 W/m2 Bottom surface 240 down

11. cT14 = 2 x 240 W/m2 240 up T0 = 255K 480 up Total energy leaving upper atmosphere 2 x 240 W/m2 Must equal energy received from lower atmosphere T1 = 304K 240 down Lower atmosphere must be hotter to balance heat shining down from upper atmosphere

12. cT24 = (480 + 480 – 240) W/m2 T0 = 255K 480 up 240 down T1 = 304K Suppose you had three layers … 720 up 480 down T2 = 337K Lower atmosphere must be hotter to balance heat shining down from upper atmosphere

13. The more layers, each just opaque enough to absorb IR radiation, the hotter the lower atmosphere is How many layers in the Earth’ atmosphere? Somewhere between 2 and 3, probably closer to 2 (well, this is a very simplified model …)

14. What controls the IR opacity of the atmosphere The concentration of greenhouse gasses: Water vapor Carbon dioxide Methane Halocarbons Nitrous oxide

15. How do you compare greenhouse Gas concentrations ? The effect on the IR opacity is what’s important Not their actual concentration in the atmosphere Standard practice – represent as an equivalent change in solar radiation, “radiative forcing”

16. Greenhouse gasses have been increasing due to anthropogenic causese.g. burningfossil fuels

18. Can future rise in atmosphericCO2 be predicted? Sources of atmospheric CO2: burning fossil fuels deforestation Sinks of atmospheric CO2: absorption into ocean forest growth

19. Spatial pattern of oceans absorption and emmission of CO2 is very variable

20. But remember … water vapor is the major greenhouse gas

21. That’s a problem for models of global warmingconcentration of water vapor very variablethey are also temperature dependenthotter climate – more water vaporbut water vapor creates clouds, which increase the earth’s albedo

22. The earth is getting hotter

24. Is the increase in radiative forcing causing this global warming n? And if so Will temperatures continue to increase as we continue to add greenhouse gasses to the atmosphere?

25. Lesson from the Ice Age: global temperature has been very variable, so Natural variation needs to be seriously considered …

26. Models of climate necessary to sort out causes But How do you build confidence that models are correctly predicting the climate system? Traditional well-controlled experiments are impractical … One approach … model the past

27. An attempt to model Last 150 year Temperature variations Requires both Natural and Anthropogenic Forcing Note big increase in Anthropogenic forcing Since 1950

30. EXEMPLARY IMPACT : SEA LEVEL RISE Light grey: parts of Mississippi Delta that are less than 5 meters below sea leavel.

32. Why Sea Level Rise? • Melting of Glaciers, especially in Greenland and West Antarctica • Huge effect: 7 meters if you melt Greenland alone • Thermal expansion of ocean waters as you heat them • Huge effect: 1 meter per deg C, if you warmed the entire world ocean down to the sea floor

33. A very large percentage ofpeople live at low elevations

34. List of Physical Impacts Temperature hotter peak temperatures fewer really cold days hotter nights Weather more droughts more intense wind in hurricanes warmer winters Precipitation more intense rain storms more evaporation, less runoff in rivers