1. Determining the Local Implications of Global Warming Clifford Mass University of Washington

2. Global Warming 101

3. What is a Greenhouse Gas? A greenhouse gas is a gas that that is relatively transparent to solar radiation, but absorbs and emits in the infrared…the type of radiation the earth emits. Some examples: –Water vapor –Carbon dioxide –Nitrous oxide –Methane

4. Partly Greenhouse Gases Make the Earth Warmer by Slowing the Loss of Infrared Radiation (infrared)

5. The Problem: Rapidly Rising Greenhouse Gases Due to Mankind

8. Amplifiers of Global Warming There are a number of natural “amplifiers” of mankind’s emission of greenhouse gases. The warming due to increased carbon dioxide, methane, and other greenhouse gases will cause more water to be evaporated from the earth’s oceans. Water vapor is the most potent greenhouse gas and thus causes even MORE warming. This is called a positive feedback

9. Even more… Warming temperatures melt snow and ice. Snow and ice help cool the planet because they reflect much of the sun’s radiation….that is why you need sunglasses while skiing. As the snow melts, less radiation is reflected to space and more is absorbed. Thus, the earth gets warmer, which melts more snow. Another positive feedback!

10. 1979 2003

11. Is Global Warming Already Happening? Finding the global warming signal is made more difficult because the earth’s climate has a substantial amount of natural variability. Also the warming due to man was relatively small prior to the middle of last century before the large increase in fossil fuel usage. The consensus of most atmospheric scientists is that some global warming due to man is now evident.

13. Eleven of the twelve warmest years in the past 150 years have occurred in the past twelve years (1995-2006)

14. But is greenhouse warming occurring in the Northwest? Finding the signal is made more difficult here by large interdecadal variability--e.g., the Pacific Decadal Oscillation.

15. Greenhouse Warming in the NW? Also there are large influences by the regions high terrain and proximity to the ocean. How do they change the story? There have been some major claims of large local effects--e.g., snowpack reduction of 50%….but are they really true?

19. But what about the future?

20. The Technology of Prediction Atmospheric scientists use complex climate prediction models…called General Circulation Models…to predict the future climate. These models are similar to weather forecast models, but allow the gases in the atmosphere to change. They also simulate the evolution of the oceans.

21. Technology of Prediction Have to assume the future emission of greenhouse gases by mankind…a major uncertainty. These models are not perfect and cannot exactly replicate the current climate….but they are close enough for useful results and getting better each year.

22. Which Scenario Will Mankind Follow?

24. Sample Climate Model Output for 2100

25. But what about the NW? What are the implications of global warming for the Northwest? How will our mountains and land-water contrasts alter the story? Do global models tell us the full story? Will there be any surprises?

26. Regional Climate Prediction As noted earlier, to understand the impact of global warming, one starts with general circulation models (GCMs) that provide a view of the global evolution of the atmosphere. Even leading GCMs only describe features of roughly 500 km or larger in scale.

27. Northwest weather is dominated by terrain and land-water contrasts of much smaller scale. In order to understand the implications of global changes on our weather, downscaling of the GCM predictions considering our local terrain and land use is required.

29. Model Topography and Resolution MM5 Topo (15 km)ECHAM5 Topo (150km)

30. Downscaling Is Needed

31. Downscaling The traditional approach to use GCM output is through statistical downscaling, which finds the statistical relationship between large-scale atmospheric structures and local weather. Statistical downscaling either assumes current relationships will hold or makes simplifying assumptions on how local weather works.

32. Downscaling Such statistical approaches may be a reasonable start, but may give deceptive or wrong answers… since the relationships between the large scale atmospheric flow and local weather might change in the future.

33. Downscaling There is only one way to do this right… running full weather forecasting models at high resolution over extended periods, with the large scale conditions being provided by the GCMs...this is called dynamical downscaling. Such weather prediction models have very complete physics and high resolution, so they are capable of handling any “surprises”

34. Downscaling Computer power and modeling approaches are now powerful enough to make dynamical downscaling realistic. Takes advantage of the decade-long work at the UW to optimize weather prediction for our region.

35. UW Regional Climate Simulations Makes use of the same weather prediction model that we have optimized for local weather prediction: the MM5. 10-year MM5 model runs nested in the German GCM (ECHAM). MM5 nests at 135 km, 45 km, and 15 km model grid spacing.

36. MM5 Model Nesting 135, 45, 15 km MM5 domains Need 15 km grid spacing to model local weather features.

37. Regional Modeling Ran this configuration over several ten-year periods: 1990-2000-to see how well the system is working 2020-2030, 2045-2055, 2090- 2100

38. Details on Current Study: GCM European ECHAM model with resolution roughly equivalent to having grid points spaced ~ 150 km apart. Can resolve features of roughly 600 km size or more. IPCC climate change scenario A2 -- aggressive CO 2 increase (doubling by 2050) IPCC Report, 2001

39. Now, The Future

49. Why Such Strong Warming on Mountain Slopes..Particularly in Spring? Probable Answer: Snow melt resulting in more solar heating.

50. Change in Water Of Snowpack (%)

53. Solar Radiation Snow and Ice Reflect Much of The Incoming Solar Radiation Now

54. Solar Radiation Global Warming Causes Snow level to Rise Resulting In Absorption of Solar Energy on Melted Slopes =WARMING Future

56. Why Relative Cooling West of Cascades in Spring? Low clouds due to more onshore flow from off the cool, cloud Pacific. The Montereyization of the western lowlands!

64. Precipitation Bottom Line: Annual trends relatively small, but some seasonal shifts

71. Early fall sees the greatest enhancement

73. Summary The viability of the approach…using high resolution numerical prediction models forced by large-scale general circulation climate models (GCMs)… has been demonstrated. Careful evaluation of the GCM output is required…there are deficiencies. Although there is general warming over the region for all seasons, the terrain and land water contrasts of the region enhance or weaken the warming in certain areas.

74. Summary Warming is enhanced on the upper windward slopes due to snow melt. Springtime warming is lessened west of the Cascade crest due to more low clouds. Many more hot days during the summer. Precipitation changes are more modest then temperature changes. There will be a substantial loss of snowpack, reaching catastrophic decreases by 2090.

75. The END

76. Project Support King County Seattle City Light EPA STAR Program Climate Impacts Group

77. We can evaluate our models by simulating the last 100 years

79. Annual Precipitation

80. Global Forcing: Surface Temperature

81. First things first But to make this project a reality we needed to conquer some significant technical hurtles. Example: diagnosing and predicting future deep soil temperatures Example: requirements for acquiring GCM output every 6 h and storing massive amounts of output. Example: insuring long-term mass conservations Evaluating the 1990-2000 simulations

82. Evaluating of Model Fidelity We have carefully evaluated how well the GCM and the MM5 duplicated the 1990-2000 period. We previously had run the system using another GCM…the Parallel Climate Model…with unsatisfactory results….crazy cold waves during the winter. ECHAM Model appears far better…but not perfect.

83. 1990-2000

84. Too Cold Cold episodes occurred 1-2 times per winter with temperature getting unrealistically cold (below 10F) in Puget Sound: Also a general cold bias to minima Better than previous attempts, but still a problem.

85. Why Cold Outbreaks? Unrealistic surges of arctic air into NW in ECHAM5, likely owing to poorly-resolved terrain (Cascades and Rockies). Extreme cold air inherited by MM5. Results from previous experiments with lower- resolution (T42) GCM indicate that higher resolution reduces frequency and severity of unrealistic cold events. Can possibly fix by extending our 45-km domain Also problem in model physics--probably more important on a daily basis

86. The Physics Fix Our research during the past few months suggests the problem was a bug in the land surface model. Fixed in the current version of model and will be used in next production runs.

87. Evaluation of Future Runs Because there are biases in the GCM runs, results for future decades (2020s, 2040s, and 2090s) will be evaluated against the ECHAM5-MM5 1990-2000 baseline But will have to be all redone once we are sure we have addressed all the problems.