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SEM seminar


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SEM seminar

  1. 1. Climate models in (palaeo-) climatic research How can we use climate models as tools for hypothesis testing in (palaeo-) climatic research and how can we apply this to understand climate change from the Cretaceous to the near future? Nanne Weber
  2. 2. Temperature 1900-2100 Different scenario’s for GreenHouse (GH) Gases +0.6C
  3. 3. History of climate last 300 Myr last 3 Myr last 1000yr last 50 kyr cold  warm
  4. 4. Outline of this talk <ul><li>What is a climate model? </li></ul><ul><li>Middle Holocene (6000 years Before Present =6 kyr BP): stable climate with warm NH summers </li></ul><ul><li>The Last Glacial Maximum (LGM, 21 kyr BP): cold, low GH Gas levels and large continental caps </li></ul><ul><li>The Paleocene-Eocene Thermal Maximum (PETM, 55 Myr BP): warm and high GH Gas levels </li></ul>
  5. 5. A climate model describes the Earth’s climate system
  6. 6. <ul><li>Computations are done on </li></ul><ul><li>a grid with finite size </li></ul><ul><li>You have to choose a grid </li></ul><ul><li>Grid size is always limited </li></ul><ul><li>Small systems are not simulated, so have to be parameterised </li></ul><ul><li>Small ~ grid distance </li></ul><ul><li>Model can only be validated at large spatial scale </li></ul>
  7. 7. <ul><li>Important processes that have to be parameterised: </li></ul><ul><li>Turbulent transport of heat, impuls, moisture </li></ul><ul><li>Clouds </li></ul><ul><li>Precipitation </li></ul><ul><li>Boundary layers </li></ul><ul><li>Radiation </li></ul>Climate models tend to be very sensitive to these processes!!
  8. 8. Completeness of model: this is determined by availability, computer resources and research question
  9. 9. Climate models Model= a set of mathematical equations which are solved on a grid by a computer *Equations describe many different processes (e.g. incoming radiation, cloud formation, heat transport, snow melt) in one or more components (e.g. atmosphere, ocean, vegetation) of the climate system *With a given spatial resolution *With given boundary conditions (e.g. glacial ice sheets, Greenhouse gases for 2100, Cretaceous land-sea mask)
  10. 10. The middle Holocene (6 kyr BP) Northern Africa wet southern Europe and India also wet , northern Europe dry
  11. 11. Het midden Holoceen Middle Holocene
  12. 12. The middle Holocene (6 kyr BP) Hypothesis: changes in precipitation (and vegetation) at 6 ka due to orbital forcing This holds also for cyclic patterns in sedimentary records
  13. 13. Orbital parameters: main cycles
  14. 14. Orbital parameters at 6kyr BP: higher NH summer insolation Changes in monthly-mean insolation as a function of latitude
  15. 15. The middle Holocene changes in summer temperature and precipitation (6k minus 0k)
  16. 16. Monsoon precipitation over Africa at 6 kyr BP: 1) models underestimate the signal as indicated by biomes 2) vegetation and ocean feedbacks help! Figure from IPCC Third Assessment Report (2001)
  17. 17. The middle Holocene (6 ka BP) Hypothesis: changes in precipitation (and vegetation) at 6 ka due to orbital forcing OK???
  18. 18. The Last Glacial Maximum LGM versus Pre-Industrial (PI) climate: lower GH-gas concentrations LGM 270 200 N 2 O ppb 760 350 CH 4 ppb 280 185 CO 2 ppm PI LGM
  19. 19. The Last Glacial Maximum (LGM) period of maximum extent of NH continental ice sheets
  20. 20. Hypothesis: changes in annual temperature and precipitation (21k minus 0k) are due to low GH-gas and ice sheets
  21. 21. Regional cooling
  22. 22. Cooling over the north Atlantic: data (diamonds) and 16 different models Figure from Kageyama et al. (2006)
  23. 23. Hypothesis OK? Yes for regional-mean cooling, but we do not (yet) understand spatial details
  24. 24. If we do a transient run, with prescribed insolation (upper), CO2 (middle) and ice (lower), do we find a realistic Antarctic temperature?
  25. 25. If we do a number of transient runs, each with separate forcings (insolation, CO2 and ice), where do we find a response to what?
  26. 26. Different aspects of climate forced by different factors!! SAT – CO2, ice Monsoon – orbital
  27. 27. What forces variations methane? One hypothesis is: variations in the wetland source Wetland area for today and LGM (Kaplan, 2002)
  28. 28. Extended hypothesis: in the cold and dry LGM climate wetland area is reduced and emissions are much lower than today
  29. 29. Methane model: compute wetland area and emissions from climatic fields (temperature, bottom moisture, etc) black: NH high-latitudes green: tropics yellow: SH high-latitudes
  30. 30. PETM: extremely warm, because of high GH-gas concentrations? Zachos et al. (2001) Large ‘mismatch’ in temperature between model (red line) and data (dots: red=PETM, yellow=just before or after PETM) Fig. from Sluijs (2006)
  31. 31. PETM simulation with EC-Earth, with CO2=1400 ppm and prescribed sea surface temperatures. Results for DJF surface temps
  32. 32. EC-Earth runs: polar warmth seems to be due to combination of feedbacks (sea-ice and snow, clouds,..) Comparison of simulated temps with data (green dots)
  33. 33. Ten Can one step twice into the same river?