1. The 100 Kyr cycle Agnes Barszcz

3. Who wants to be a climatologist? 2 teams: The Aphelions The Perihelions Rules Joker

4. What I am going to talk about Various hypotheses for 100 kyr cycle Why Milankovich is wrong Suggest a new hypothesis See if it is reasonable Look at it’s sensitivity to different parameters Its flaws What is the right theory FUN: Giving out the price!!!

5. What is the 100 kyr cycle?

6. What is causing it? Many hypothesies: The milankovitch cycle Isostatic adjustmets of the litosphere under the weight of the glacier Feedback between atmosphere ocean and Co2 ….. WE ARE STILL MISSING A SOLUTION!

7. Question 1: Who can tell me in less then 2 minutes what the Milankovich theory is ?

8. Milankovich and and why it is wrong! 3 components Eccentricity Precession Axial tilt

9. Which one was key for us?

10. Milankovich and and why it is wrong! 3 components: Eccentricity would be the one we are interested in! -> Top five reasons that we should NOT……

11. Spectrum of 100-kyr glacial cycle: Orbital inclination,not eccentricity. By RICHARD A. MULLER* AND GORDON J. MACDONALD http://www.pnas.org/cgi/reprint/94/16/8329.pdfhttp://www.pnas.org/cgi/reprint/94/16/8329.pdf, 1995 Eccentricity changes are small Orbital calculation when caried out with greater presision show a major cycle of 400 Kyr Well dated climate proxies show a 100 kyr cycle only over the last million of years Double peak in frequency domain Causality problem

13. Suggested solution: Changes in the orbital inclination

14. Find a suitable solution…

15. Methods Use simple or complex models

16. Pros and cons Complex models: Global circulation models Pro: They take into account many parameters. They are more realistic Cons: Require large computers $$$$$ -> Used to simulate equilibrium responses to various initial conditions

17. Pros and cons Simple models: Pro: Require less computer power, and run faster.. Con: Yield less realistic results. We do not see the influence of all the small parameters that we have neglected

18. What was used A simple model

19. Claim Hezi Gildor and Eli triperman say the 100 kyr cycle is NOT related to the milankovich cycle!!!!!!!!

20. The answer! Their hypothesis is: The variation of the ice-albedo between glacial and interglacial periods Variant of the precipitation-temperature feedback

21. What the autors used A simple zonaly averaged box

22. The components of the model Ocean meridional thermohaline circulation Atmospheric temperature-humidity feedback Land glaciers Sea ice

23. What,where,how? The ocean model 4 surface boxes (400 m) 2 polar: Water may be covered with sea ice of variable extent Land may be covered with land ice of variable extent 2 midlatitude boxes 4 Deep water boxes (4000 m) ** Important to note that the ablation rate of glacier stays constant with time….

24. What,where,how? The atmosphere model: Each box can have 4 types of lower surfaces: Land Ocean Land Ice Sea ice -> All have different albedos

25. The technicalities What is a leapfrog scheme?

26. Leapfrog

27. Why leapfrog? Time reversible Assures energy conservation A better accuracy http://www.lifelong-learners.com/pde/SYL/s2node4.php http://einstein.drexel.edu/courses/CompPhys/Integrators/leapfrog/

28. How it goes… The crux of the problem

29. How it goes: Ocean is ice free Temperatures are mild More precip then melting and carving ->-> Land ice sheet grows

30. How does that affect the temperature?

31. As ice sheet grows slowly The albedo of the earth decrease The sea temperature are below zero only in the polar boxes. ->->-> At year 90 kyr, the global SST reaches zero degrees

32. What’s special about the moment that the SST reaches zero?

33. Ice sheet rapidly grows As the SST attained a critical value, sea ice grows very rapidly! In 20 year all polar box is covered in sea ice. ->->-> Sea ice switch is ON

34. When the switch is on.. Sea Ice Stop growing!!! Why????

35. Self-limitation of sea ice The sea cools by giving out heat to the atmosphere When it is covered by ice, there is no more exchange The warm midlatitude waters mix with the polar waters ->->-> No more sea ice growth

36. The ice age! The glacier is at it’s maximum The atmosphere is at it’s coldest How do we get out of an ice age??

37. Moisture feedback There is less moisture captured by cold air, so less northward moisture transport Because of the ice cap, there is also less evaporation in the polar region ->->-> Less moisture present in polar regions

38. We are loosing the icesheet The precipitaion rate is reduced by ½ The ablation rate stays constant ->->-> The glaciers retract

39. On the road to warm times As the ice sheet retract, the albedo is decreasing. Atmospheric and ocean temperatures rise slowly. As long as there are ice sheets in polar region the ocean temperature in the region in below zero :sea ice is present. -> How does that affect the land ice sheet?

40. Further down, on the road to warm times.. As long as the ice sheet is there, the land glaciers retreat fast The sea ice, does melt by sloooowly… The meltdown is slow because the SSt is close to zero.. -> What is causing it to melt anyways?

41. Close to interglaciation.. The sea ice melts down because of the heat advected and diffused by the ocean, that is coming from the midlatitudes. ->What will cause the abrupt acceleration of the melt down of sea ice?

42. Deep Ocean Because the deep ocean heats up: But Why?

43. The deep ocean Because of the melt down of the land ice sheet The switch is OFF

44. Switch is “off” All the ice melts down in about 40 years Atmosphere and ocean temperatures rise again

45. And back… The temperatures are maximum The ice sheet is minimum The amount of precipitation is at it’s maximum ->We are back at the starting point!

46. The Results Simulated years from 170 kyr to 70 kyr

47. Theoretically it makes sense… Ok so we have a scheme… Does it practically?

48. So what about the THC?!? THC = Thermohaline circulation It was included in the model It is rather an effect the a cause of the 100 kyr cycle What changes the strength of the THC?

49. The THC strength When glaciers melt, there is a lot of fresh water relised: minimal THC (12Sv) At interglacial periods, there is a lot of evaporation: Salier water: strong THC(16Sv) When glaciers form: less evaporation: weaker THC(13Sv)

50. Is it an ok resolution to have only 4 boxes? How many did we use in the model we made in class?? It is only the upper part of the ocean that has to cool significantly for glaciation. (The lower part’s role is to provide delayed responses to various forcing) It was already demonstrated in previous papers that this can be achieved in only a few tens of years

51. Does it make sense to have a 100 kyr period? Let’s do some simple math!!!!! Volume of land glaciers:  V= V max –V min =2.4 e16 m 3 M-Accumulation rate maximum = 0.09 e6 m 3 /s minumum = 0.03 e6 m 3 /s S-Ablation rate

52. Sensitivity to different parameters

53. Land–Ice sink term Reduce by 4 % Reaches faster the critical value at which the ice starts growing Slower deglaciation -> Cycle is longer by 10 kyr -> Less saw-tooth like shape

54. Land–Ice sink term Increase by 20 % Sink term always exceeds the precipitation rate ->>Glacier disappears!!!

55. Albedo Increase both land ice and sea ice albedo What will happen??

56. Albedo Increase both albedos Shorter cycle Less land ice needed to reduce SST under the threshold value Glaciers need to become smaller then before to enable a temperature increase that results in ice melting -> Shorter growth/Longer meltdown ->Shorter but more symmetric cycle

57. Albedo Very significant increase in sea ice albedo -> Permanent sea ice cover ->No land Ice

58. Albedo Very significant decrease in Sea ice albedo -> Makes the sea-ice mechanism less effective as a switch

59. Albedo Increase in Land-ice albedo ->Reduces the amplitude of the oscillation and shortens the time scale Converse is true

60. Emissivity The long wave emissivity represents: Cloud cover Humidity Land cover Topography Aerosols CO2 How will the emissivity evolve between a glacial minimum and maximum?

61. Emissivity The emissivity will increase between a glacial minimum and a glacial maximum because there is a smaller water vapor concentration

62. How about the CO2? Pelletier and Marshall: P’=0.015*ln( CO2 / CO2 ref ) So for a 30% CO2 change P changes by - 0.003 Induces an increase in the time scale of the oscillation of about 9 kyr. -> Why longer?

63. How about the CO2? Why longer? Whole system is warmer, We will need larger glaciers to turn the switch on!!

64. How about CO2? If we change P by +0.003 Cycle is longer by 12 kyr If we change P by + 0.005 Cools the climate enough so there is a permanent sea-ice cover

65. Ice sheet thickness?

66. Ice sheet thickness Doesn’t change the cliamte! Ice sheet play there role by the albedo Insulating properties

67. Freezing temperature Similar effect as with the emissivity Lowering the freezing T by 0.5 o Time scale is longer by 20 kyr Increasing the freezing T by 0.5 o Time scale is shorter by 20 kyr

68. Problems The model is Quite simple Highly idealized Neglecting any zonal variations Limited set of feed-backs

69. Problems…. It is not synchronous with observations Fails to predict the synchronous deglaciation of the southern hemisphere BUT

70. Take home message The aim of a such a simple model is NOT to be accurate with observations but just to explore potentially IMPORTANT effects and feedback of the climate.