Future Climate Change in the Pacific Northwest

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 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 1-4Fand 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 Natural & Anthropogenic Mainly Natural

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

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 timeSvante Arrhenius, 1896

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

17. Greenhouse gases act like a blanketThicker 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 ModelingWhere we run high-resolution local models driven by global climate simulations.

25. Change in Winter Surface Air Temperatures (F)

29. TemperatureNorthwest warming delayed and slowed by the Pacific Ocean Observed Winter Surface Temperature Change (1975-2014)

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. 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 Precipitationon 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