Future Climate Change in the Pacific Northwest Cliff Mass, Atmospheric Sciences University of Washington

There has been a great deal of contradictory information about global warming and its influence on the Northwest

What can climate prediction science tell us. What do we know for sure What can climate prediction science tell us? What do we know for sure? What are the uncertainties? Can you true the media?

Human-forced (anthropogenic) climate change has already affected our region Even without any effects from increasing greenhouse gases like CO2

Massive Irrigation in Eastern WA

The result: cooling of 1-4F and higher humidity

Seattle’s urban core is 2-10F warmer due to concrete and buildings

Bottom Line Humans have already changed the weather and climate due to changes at the surface

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.

NOAA observations over the NW Mainly Natural Natural & Anthropogenic

The Pacific Decadal Oscillation: A Mode of Natural Variability More snow Less Snow

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.

Anthropogenic Climate Change Resulting from Increasing Greenhouse Gases

Greenhouse gases warm the planet Carbon Dioxide Water Vapor Methane Nitrous Oxide … and others Greenhouse Gas Emissions

The basic physics has been known for a long time Svante Arrhenius, 1896

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

Greenhouse gases act like a blanket Thicker blankets (or more of them) make you warmer

CO2 concentrations are increasing rapidly

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.

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.

Climate Model Output for 2100

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.

Problem: Global climate models are too coarse to simulate the effects of critical Northwest terrain Climate Model Terrain

A new technology to solve the resolution issue: Regional Climate Modeling Where we run high-resolution local models driven by global climate simulations.

Change in Winter Surface Air Temperatures (F) 25

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

Without Pacific warming, our mountain snowpack has not changed much over the past 30 years

What about water, our most precious resource?

Good news for average precipitation Unlike some areas, we will still have plenty of precipitation, just more rain and less snow

Change in Snowpack from 1990 to 2090 But warming will result in more precipitation falling as rain rather than snow Change in Snowpack from 1990 to 2090 Lower 0% Higher

DON’T BUY THIS IN 2050

But there is a dark side to the our future warmth: more extreme precipitation and flooding

Super Atmospheric Rivers

When atmospheric rivers hit our terrain, intense precipitation falls Precipitation on extreme atmospheric river days increases by 15-39%

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.

And Greater Risk of Slope Failures and Landslides Oso Washington

Northwest Windstorms Will there be more of them? Will they become more intense? The Inauguration Day Storm 1993

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

Sea Level Rise Best estimates are 1-2 feet between 2000 and 2100, assuming continued greenhouse gas increases.

But it is a bit more complicated..

Slow Rise (2 mm a year, 8 inches a century)

Relatively minor impacts overall because our land rises rapidly from the water in most locations

Northwest Wildfires and Climate Recent increase in large wildfires, but the small increase in temperature does not explain it.

More fires in the early 20th century followed by suppression

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

Increasing Wildfire Risks Huge increases of population in the urban/fire interface Large increase of recreation use of forests.

Wildfires But later in the century, warming temperatures, less snowpack and drying summers could enhance wildfire probabilities on both sides of the Cascades.

Dealing with Global Warming Mankind is doing little to stop global warming. Substantial impacts will occur, but there is considerable uncertainty regarding the magnitude and impacts even if we knew the future of greenhouse gases in the atmosphere.

The Media is Doing A Very Poor Job Informing About Global Warming Science and Impacts Much of what is available from online media, print media (e.g., Seattle Times), and broadcast media (e.g., CNN) is wrong, exaggerated, or inaccurate. This is particularly true regarding global warming impacts on extreme events. Several politicians are worse.

Major Points Global warming from increasing greenhouse gases will be very significant, particularly later in the century The Northwest is a relatively favored area, with slow change and plenty of water Efforts for adaptation and resilience can greatly reduce the risks.

The End