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

Some environment groups have proposed that global warming has already caused our precipitation to become more extreme

And local media have aired stories saying storms are getting more intense

In contrast, others hold that there is no strong evidence for current or future changes ill

Some suggest that the recent “pause” means global warming is not occurring

…while thousands of scientists from around the world have written a series of reports indicating the imminent threat of global warming due to mankind’s influence

Intergovernmental Panel on Climate Change (IPCC) Reports

What can climate prediction technology tell us What can climate prediction technology tell us? What do we know for sure? What are the uncertainties? What will happen here?

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

Massive Irrigation in Eastern WA

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

Plowed fields: Eastern WA dust storms

Seattle’s urban core is often 2-10F warmer than it would have been without concrete and buildings

Bottom Line Humans have already changed the climate

Increasing Greenhouse Gases

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

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

CO2 oncentrations are increasing rapidly

We predict the impacts of increasing greenhouse gases using global climate models (GCMs) Sophisticated computer simulations based on the physics of the atmosphere and ocean. Atmospheric parts are nearly identical to weather prediction models, which are tested every day, but with atmospheric gases vary in time.

Climate Prediction Technology We run coupled 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 22

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.

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 30 yr

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

Change in Winter Surface Air Temperatures (F) 28

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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

NCAR Global Model (Winter Precipitation Trend, 2005-2060)

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 -40% 0% +40%

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

Global warming will intensify atmospheric rivers Warmer air holds more water vapor. Examined a large collection of climate models simulation for changes from 1970-2000 to 2070-2100 based on “business as usual” greenhouse gas emissions. 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.

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. UW investigated this issue for Seattle City Light

Can we predict climate decades ahead when we can’t forecast next week’s weather?

In weather prediction we forecast the exact state of the atmosphere at some time in the future Tomorrow’s high in Spokane will be 67F It will rain tomorrow afternoon after 3 PM

In Climate Prediction We DON’T Do This We predict average quantities over extended periods. Example: the mean winter temperatures will be 3F higher over the Pacific Northwest. The average conditions are closely controlled by the amount of radiation reaching and leaving the planet We have a good handle in changes in radiation, IF WE KNOW THE ATMOSPHERIC COMPOSITION.

Major Take Home Messages Global warming from greenhouse gases has had only a small influence on our region so far. Natural variability has dominated over human forcing. That will change, particularly by the end of the century. Less warming near the coast, more in eastern Washington. Think 3-8F during the winter. Annual precipitation will remain the same or increase slightly

Take Home Significant (30-70%) drops in mountain snowpack by the end of the century Atmospheric rivers will be stronger, with heavier rainfall and more flooding. No increase in windstorms Beware those that hype current weather events as indications of global warming. Those who claim that GW is not an issue are equally wrong.

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