Climate Change in the Pacific Northwest: Impacts and Planning Philip Mote UW Climate Impacts Group University of Washington Climate Science in the Public Interest

Science of climate change  Thousands of peer-reviewed scientific papers  Intergovernmental Panel on Climate Change (IPCC)  Major reports in 1990, 1996, 2001  Conclusions:  “An increasing body of observations gives a collective picture of a warming world and other changes in the climate system.”  “There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.”

Carbon dioxide: up 32%

Methane: up 150%

Global average temperature degrees Celsius

Could these measurements be wrong?  Urbanization?  Stations too sparse?  Satellite measurements show no warming?  Perhaps 10% of warming; lots of natural evidence  Warming patterns very big  Surface definitely warming; troposphere warming but not

The South Cascade glacier retreated dramatically in the 20th century Courtesy of the USGS glacier group

Trends in timing of spring snowmelt ( ) Courtesy of Mike Dettinger, Iris Stewart, Dan Cayan +20d later –20d earlier

Mote 2003(b) Decrease Increase

those satellite observations Models: troposphere should warm faster than surface But satellites show little warming (0-5 miles) since 1979: does this mean that surface measurements are unreliable?

those satellite observations Models: troposphere should warm faster than surface But satellites show little warming (0-5 miles) since 1979: does this mean that surface measurements are unreliable?

Some evidence that it’s not natural  Rate of change appears to be unusual  Pattern of change matches that expected from increasing greenhouse gases  Solar, volcanic forcing would have led to cooling in the past ~30 years

Long-term context source: Mann et al., EOS

Carbon dioxide: up 32%

Solar output varies - but not much Figure courtesy of NOAA National Geophysical Data Center

Natural Climate InfluenceHuman Climate Influence All Climate Influences

Temperature change, minus

Main Impact: Less Snow April 1 Snow Extent for the Columbia River Basin Less snow, earlier melt:  More water in winter  Less water in summer

Snake River at Ice Harbor Reduced summer flows ==> shortages for irrigation, fish, hydro; less concern over flooding Increased winter flows ==> more hydro production

Simulated Natural Flow in the Willamette River at the Confluence with the Columbia

Conclusions  Earth is warming as greenhouse effect strengthens  Regional climate change will take many forms, some of which we cannot predict  Warming is virtually certain and has profound impacts: loss of snowpack, reduction in summer water supply, hardships for salmon and forests  Some prudent steps can be taken now to reduce vulnerability

Enhanced greenhouse effect

Decrease Increase

and climate damage Floods Estuary conditions: prey, predators, competitors Low summer streamflow, high temp ????

Consequences  Reduced summer flow in most rivers is likely  More difficulty supplying water for agriculture, hydropower, fish, recreation  Likelihood of snow-driven (springtime) flooding will decrease  Likelihood of rain-driven (winter) flooding will increase

21 st century temperature change IPCC (

Projected PNW Climate Change 2020sTemperaturePrecipitation Low+ 0.5°C+ 1.5 % Mean+ 1.5°C+ 6.9% High+ 2.5°C % 2040sTemperaturePrecipitation Low+ 1.5°C- 3.3 % Mean+ 2.3°C+ 7% High+ 3.2°C % Based on an increase in equivalent CO 2 of 1% per year. Benchmarked to the decade of the 1990s. Projected changes in average annual PNW temperature and precipitation for the decades of the 2020s and 2040s.