1. Future Climate Change in the Pacific Northwest
Cliff Mass, Atmospheric Sciences
University of Washington

2. There has been a great deal of contradictory information about global warming and its influence on the Northwest

3. What can climate prediction science tell us. What do we know for sure
What can climate prediction science tell us? What do we know for sure? What are the uncertainties? Can you true the media?

4. Human-forced (anthropogenic) climate change has already affected our region
Even without any effects from increasing greenhouse gases like CO2

5. Massive Irrigation in Eastern WA

6. The result: cooling of 1-4F and higher humidity

7. Seattle’s urban core is 2-10F warmer due to concrete and buildings

8. Bottom Line
Humans have already changed the weather and climate due to changes at the surface

9. Natural Variability
Even without humans, weather and climate would vary in time, and records would be broken.
To understand anthropogenic global warming, one must start with a knowledge of natural variations.

10. NOAA observations over the NW
Mainly Natural
Natural & Anthropogenic

11. The Pacific Decadal Oscillation: A Mode of Natural Variability
More snow
Less Snow

12. Climate Change in the Northwest
Past climate change in the NW was mainly the result of natural variability and human impacts on surface conditions
But there is now a new player, whose impacts will increase in time.

13. Anthropogenic Climate Change Resulting from Increasing Greenhouse Gases

14. Greenhouse gases warm the planet
Carbon Dioxide
Water Vapor
Methane
Nitrous Oxide
… and others
Greenhouse Gas Emissions

15. The basic physics has been known for a long time Svante Arrhenius, 1896

16. We understand the greenhouse effect
Graphic courtesy of the National Park Service

17. Greenhouse gases act like a blanket Thicker blankets (or more of them) make you warmer

18. CO2 concentrations are increasing rapidly

19. We can predict the impacts of increasing greenhouse gases using global climate models
Sophisticated computer simulations based on the physics of the atmosphere and ocean.
Atmospheric parts are nearly identical to weather prediction models, but with atmospheric gases varying in time.

20. Climate Prediction Technology
We run global atmosphere-ocean models for decades or centuries.
Use the most powerful supercomputers.
Have to make assumptions about greenhouse gas emissions. How will they change in time?
There about two-dozen international groups doing such simulations.

21. Climate Model Output for 2100

22. Global Warming is NOT Uniform
Arctic warms quickly for a number of reasons, including the melting of sea ice.
Continents warm up more than oceans.
Eastern oceans up less than western oceans.
In general, the dry areas (e.g., the SW U.S.) get drier and wet areas (e.g., British Columbia) get wetter.

23. Problem: Global climate models are too coarse to simulate the effects of critical Northwest terrain
Climate Model Terrain

24. A new technology to solve the resolution issue: Regional Climate Modeling Where we run high-resolution local models driven by global climate simulations.

25. Change in Winter Surface Air Temperatures (F)25

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29. Temperature Northwest warming delayed and slowed by the Pacific Ocean
Observed Winter Surface Temperature Change ( )

30. Without Pacific warming, our mountain snowpack has not changed much over the past 30 years

31. What about water, our most precious resource?

32. Good news for average precipitation
Unlike some areas, we will still have plenty of precipitation, just more rain and less snow

34. Change in Snowpack from 1990 to 2090
But warming will result in more precipitation falling as rain rather than snow
Change in Snowpack from 1990 to 2090
Lower 0%
Higher

35. DON’T BUY THIS IN 2050

36. But there is a dark side to the our future warmth: more extreme precipitation and flooding

37. Super Atmospheric Rivers

38. When atmospheric rivers hit our terrain, intense precipitation falls
Precipitation on extreme atmospheric river days increases by 15-39%

39. Flooding Potential Increases
Snow absorbs rain.
With less snow, there will be less “protection.”
Thus, heavier rainfall could lead to greater flooding on major rivers.

41. And Greater Risk of Slope Failures and Landslides
Oso Washington

42. Northwest Windstorms Will there be more of them?
Will they become more intense?
The Inauguration Day Storm
1993

43. Northwest Windstorms
The answer appears to be no. No increasing trend in observations and none suggested by climate models.
UW investigated this issue for Seattle City Light

44. Sea Level Rise
Best estimates are 1-2 feet between 2000 and 2100, assuming continued greenhouse gas increases.

45. But it is a bit more complicated..

46. Slow Rise (2 mm a year, 8 inches a century)

47. Relatively minor impacts overall because our land rises rapidly from the water in most locations

48. Northwest Wildfires and Climate
Recent increase in large wildfires, but the small increase in temperature does not explain it.

49. More fires in the early 20th century followed by suppression

50. Increasing Risk of Major Wildfires
Climate change is a small part of this.
Suppression has produce unhealthy forests with lots of fuels ready to burn.
Now
Original

51. Increasing Wildfire Risks
Huge increases of population in the urban/fire interface
Large increase of recreation use of forests.

52. Wildfires
But later in the century, warming temperatures, less snowpack and drying summers could enhance wildfire probabilities on both sides of the Cascades.

53. Dealing with Global Warming
Mankind is doing little to stop global warming.
Substantial impacts will occur, but there is considerable uncertainty regarding the magnitude and impacts even if we knew the future of greenhouse gases in the atmosphere.

54. The Media is Doing A Very Poor Job Informing About Global Warming Science and Impacts
Much of what is available from online media, print media (e.g., Seattle Times), and broadcast media (e.g., CNN) is wrong, exaggerated, or inaccurate.
This is particularly true regarding global warming impacts on extreme events.
Several politicians are worse.

55. Major Points
Global warming from increasing greenhouse gases will be very significant, particularly later in the century
The Northwest is a relatively favored area, with slow change and plenty of water
Efforts for adaptation and resilience can greatly reduce the risks.

56. The End