Climate Change in the Pacific Northwest: Impacts and

Planning

Philip Mote UW Climate Impacts GroupUniversity 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

1860 1880 1900 1920 1940 1960 1980 2000

0.8

0.4

0

-0.4

-0.8

degr

ees

Cel

sius

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 1960-2001 but not 1979-2001

1928

2000

The South Cascade glacier retreated dramatically in the 20th century

Courtesy of the USGS glacier group

Trends in timing of spring snowmelt (1948-2000)

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 Influence Human Climate Influence

All Climate Influences

Temperature change, 2071-2100 minus 1961-1990

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

0

20000

40000

60000

80000

100000

120000

140000

O N D J F M A M J J A S

Flo

w (

cfs

)

base

comp 2020

comp 2040

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

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

N2O

O3

CFCs

CH4

CO2

W/m2

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

21st century temperature change

IPCC (www.ipcc.ch)

Projected PNW Climate Change

2020s Temperature

Precipitation

Low + 0.5°C + 1.5 %

Mean + 1.5°C + 6.9%High + 2.5°C + 14.4 %

2040s Temperature

Precipitation

Low + 1.5°C - 3.3 %

Mean + 2.3°C + 7%High + 3.2°C + 13.7 %

Based on an increase in equivalent CO2 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.