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

meter meter

Source: IPCC

Average global temperature has increased 0.8°C since IPCC (2007)

Average global temperature has increased 0.8°C since 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: °C Warming expected through 21st century even if CO 2 emissions end today due to persistence of greenhouse gases Projected 21 st Century Global Warming

Projected Temperature in Northwest Changes relative to °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-21 st century Choice of emissions scenario matter more after 2050s

Winter winds and pressure over the North Pacific Summer winds and pressure over the North Pacific Aleutian Low Subtropical High H H L L

El Niño Southern Oscillation For the Pacific Northwest: Positive (El Niño) = Warm, dry winter Negative (La Niña) = Cool, wet winter Southern Oscillation Index

Pacific Decadal Oscillation An El Niño-like pattern of climate variability year periods of persistence in North American and Pacific Basin climate Warm, dry Cool, 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 the Cascades and Olympics has retreated during the past years Photos courtesy of Dr. Ed Josberger, USGS Glacier Group, Tacoma, WA South Cascade Glacier, 1928 (top) 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

Thresholds 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 responses Annuals & weedy species ↑ Deciduous and sprouting species ↑ Fire-sensitive species ↓ Specialists with restricted ranges ↓ Climate change Warmer temperature More severe droughts Fire resets succession, alters temporal scale of fire rotation. Mature trees buffer effects of warmer climate without disturbance. Habitat changes Landscape homogeneity ↑ Fire-adapted species ↑ Forest cover ↓ Species refugia ↓ New fire regimes Fire 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.,

Fire suppression  Fire exclusion  Fuel accumulation

Cool PDOWarm PDO Area burned – Western U.S., Fire suppression  Fire exclusion  Fuel accumulation

Cool PDOWarm PDO Area burned – Western U.S., 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, 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: Analysis of wildfire data since 1916 for the 11 contiguous Western states shows that for a 2.0 o C 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

Mountain Pine Beetle outbreaks British Columbia Courtesy of Mike Bradley, Canfor Corporation

Forest carbon budgets Storage (quantity) vs. uptake (rate) Young forest Storage Uptake Mg/ha Mg/ha/yr Old forest

Options for planners and resource managers???