Effects of Climate Change on Pacific Northwest

Ecosystems

Dave Peterson

Climatic Variability and Change – A Brief Introduction

Radiative Forcing Components of Global Warming

1.6 Watts

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Source: IPCC

Average global temperature has increased 0.8°C since 1906.

IPCC (2007)

Average global temperature has increased 0.8°C since 1906.

IPCC (2007)

Warmest 12 years 1998,2005,2003,2002,2004,2006, 2001,1997,1995,1999,1990,2000

Data source: IPCC 2001

IPCC “best estimate” range of global-scale warming by the 2090s:

1.8 - 4.0°C

Warming expected through 21st century even if CO2 emissions end today due to persistence of greenhouse gases

Projected 21Projected 21stst Century Global Warming Century Global Warming

Projected Temperature in Northwest

Changes relative to 1970-1999

7.2°F

3.6°F

0°F

10.8°F

14.4°F

+1.2ºC

+1.9ºC (

+3.3ºC (

°C

Rate of change per decade expected to be 3 times greater through mid-21st century

Rate of change per decade expected to be 3 times greater through mid-21st century

Choice of emissions scenario matter more

after 2050s

Winter windsand pressure over the North Pacific

Summer windsand pressure over the North Pacific

Aleutian Low Subtropical High

HH

LL

El Niño Southern Oscillation

For the Pacific Northwest:Positive (El Niño) = Warm, dry winterNegative (La Niña) = Cool, wet winter

Southern Oscillation IndexSouthern Oscillation Index

Pacific Decadal Oscillation

• An El Niño-like pattern of climate variability

• 20 - 30 year periods of persistence in North American and Pacific Basin climate

Warm, dryWarm, dry

Cool, wetCool, wet

Droughts were more common prior to 1950

Gedalof et al. (2004)

Streamflow for the Columbia River, reconstructed from tree-ring data

Why extremes matter

Standard deviation

1 in 40 yr high range

The distribution of weather events around the climatic average often follows a ‘bell-shaped’ curve.

Climate change can involve change in the average, or the spread around the average (standard deviation), or both.

A shift in the distribution

of temperatures has a much larger relative effect at the extremes than near the mean.

A shift of 1 standard deviation makes a 1 in 40 yr event into a 1 in 6 yr event

3.6°F

2.7°F

1.8°F

0.9°F

cooler warmer

Temperature trends (°F per century) since 1920

Nearly every glacier in Nearly every glacier in the Cascades and the Cascades and

Olympics has retreated Olympics has retreated during the past 50-150 during the past 50-150

yearsyears

Photos courtesy of Dr. Ed Josberger, USGS Glacier Group, Tacoma, WA

South Cascade South Cascade Glacier, 1928 (top) Glacier, 1928 (top)

and 2007 (right)and 2007 (right)

Snow Water Equivalent Trends

• Most PNW stations show a decline in snow water equivalent

• Numerous sites in the Cascades with 30% to 60% declines

Decrease Increase

Altered Streamflow• More winter rain, less snow → higher winter

streamflows• Warmer temperatures → earlier snowmelt and shift in

timing of peak runoff

+3.6 to +5.4°F(+2 to +3°C)

Projected streamflow changes, 2050s

Forest vegetation varies over time

The Disease Spiral

From Manion (1991)

A pathological model is applicable to forest ecosystems

Warmer climate

Soil moisture stress (+)

Growth and vigor (-)

Growth and vigor are affected by human-related factors

Exotic plants, pathogens, insects

Forest harvest practices

Air pollution

Fire exclusion

Critical Threshold

Time

Temperature Increase

Climatic VariabilityCli

mat

eThresholds are important

Pinyon pine - juniper Jemez Mountains, NM

October 2002

Pinyon pine dead Jemez Mountains, NM

May 2004

Climate change and tree growth

Subalpine forests

Westside forests

Low elevation forests

Mid elevation forests

Eastside forests

Subalpine forests: Less snowpack; longer, warmer growing seasons = Growth increase

Mid elevation forests: Warmer summers, less snow pack = Depends on precipitation

Low elevation forests: Warmer summers, less snow pack = Large growth decrease

Species responsesAnnuals & weedy species ↑Deciduous and sprouting species ↑Fire-sensitive species ↓Specialists with restricted ranges ↓

Climate changeWarmer temperatureMore severe droughts

Fire resets succession, alters temporal scale of fire rotation.

Mature trees buffer effects of warmer climate without disturbance.

Habitat changesLandscape homogeneity ↑Fire-adapted species ↑Forest cover ↓Species refugia ↓

New fire regimesFire frequency ↑Extreme events ↑Area burned ↑

Disturbance drives ecosystem change

The disturbance pathway is faster

How will climate change affect wildfire?

Area burned – Western U.S., 1916 - 2007

Area burned – Western U.S., 1916 - 2007

Fire suppression Fire exclusion Fuel accumulation

Cool PDOWarm PDO Warm PDO

Area burned – Western U.S., 1916 - 2007

Fire suppression Fire exclusion Fuel accumulation

Cool PDOWarm PDO Warm PDO

Area burned – Western U.S., 1916 - 2007

Fire suppression Fire exclusion Fuel accumulation

Lots of fire Much less fire Lots of fire

Years with fire area > 80,000 hectares

National Forest data, 1916-2007

Warm-phase PDO Cool-phase PDO

Idaho 15 7

Oregon 14 5

Washington 11 2

TOTAL 40 (74%) 14 (26%)

Future wildfire?

McKenzie et al. (2004), Conservation Biology 18:890-902

Analysis of wildfire data since 1916 for the 11 contiguous Western states shows that for a 2.0oC increase that annual area burned will be 2-3 times higher.

Fire – a component of stress complexes

Lodgepole pine forest

McKenzie et al. (2009)

Effects of temperature increase on mountain pine beetle

• Population synchronized by temperature (onset of spring)

• Rate of generation turnover increases with temperature increase

Tree Mortality

Mountain Pine Beetle

Shaded areas show locations where trees were killed. Intensity of damage is variable and not all trees in shaded areas are dead. www.fs.fed.us/r6/nr/fid/data.shtml

1980 - 2004

Mountain Pine Beetle outbreaks British Columbia

Courtesy of Mike Bradley, Canfor Corporation

Forest carbon budgetsStorage (quantity) vs. uptake (rate)

Young forest Storage Uptake Mg/ha Mg/ha/yr

50-100 5-10

Old forest 400-1000 + 1.0

Options for planners and resource managers???