June 24, 2019

The Best Estimate Yet of the Impact of Global Warming on the Pacific Northwest

During the past month, a group of atmospheric researchers in my group at the University of Washington have completed a series of high-resolution climate simulations that probably represent the best estimate to date of what global warming, forced by increasing greenhouse gases, will mean for the Northwest.
CO2 is increasing more rapidly then ever

This blog will explain what we have done and how it provides a superior tool for determining the regional implications of anthropogenic (human-forced) climate change.  Securing a realistic estimate of the local impact of global warming is critical if we are to take steps to ensure resilience to the expected changes.  And yes, it might motivate folks to reduce their carbon footprint (like reducing jet travel, using mass transit more, etc.)

Before I begin, let me note that much of this work was sponsored by an Amazon Catalyst grant, which supported two UW staff members (Richard Steed and Jeff Baars) who ran and analyzed the simulations.   Amazon also provided substantial cloud computing resources.

Most estimates of climate change begin and end with global climate models, which include both atmospheric and ocean modeling components.  These global models are driven by estimates of how greenhouse gases, like CO2, will increase in the future.

But there is a problem.  To run globally for a century or more, the climate models must sacrifice spatial resolution.  In fact, most global models are run with grid spacing of around 150 km, which makes them unable to simulate the impacts of the crucial terrain and land-water features of the Pacific Northwest.  

We are talking about no Cascades, no Olympics, no Puget Sound or Strait of Juan de Fuca.  Even the Rockies are too low and smeared out.   Not good.  One thing my group at the UW has shown is that you have to run weather prediction models with roughly 12-km or better grid spacing to have any chance of getting our local weather and climate correct. The picture below illustrates the difference in terrain between a climate model (e.g., NCAR's CCSM4) and a higher-resolution weather prediction model.

A number of research projects have only made use of one or two climate models.  But each model has its uncertainties and biases; it would be far better to look at a collection (or ensemble) of model results--just as it is better to look at an ensemble of weather prediction forecasts.

The UW Effort:  An Ensemble of High-Resolution Climate Simulations

To address these issues, our group took on a complex task:  to run a high resolution weather forecast model for 130 years (1970-2100).   But instead of running the high-resolution model globally, which would have required impossible computer resources, we ran it over a domain that includes only the Pacific Northwest (see domains above).  And we did this 12 times, each driven by a different climate global model, allowing us to get a handle on the uncertainty in the climate forecasts.  There are fancy names for what we did:  dynamical downscaling or regional climate modeling.

We started with the several dozen global models that were part of the international CMIP-5 effort and selected the twelve that verified the best over the eastern Pacific during a contemporary period (1970-2000) and had output every six hours (which we needed to drive our regional climate model).

But we had a major decision to make.  How aggressive an increase in greenhouse gases should we use?   Should we assume that folks would "get religion" about climate change and radically reduce their emissions or should we use a "business as usual" continuation of recent trends?

We decided to go with the latter, in order to delineate the worst case.  So we used the RCP 8.5 scenario, which assumes continued increases of emissions (see below).   For the next few decades, the emission scenarios are all similar, since

 mankind can't change our energy technologies quickly, but by the end of the century the differences are large. 

Let me say, that I believe that the RCP 8.5 scenario will turn out to be too pessimistic (aggressive) by the middle to the end of the century.  I suspect that advancing technologies (like better photovoltaics, the advent of fusion power, advances in removing CO2) will have a major impact 30-60 years from now in reducing CO2 emissions and concentrations.   There will be advances that we can not even imagine now.

So consider what I am about to show as the worst case---and that the actual changes will not be so extreme.

Some Results

I will start by showing you the difference in conditions between a recent period (1970-1999) and two future periods (2030-2059, 2070-2099).    I show such thirty year periods to average out short-term variations that have little to do with climate trends. And I will present averages of the 12 climate runs.

Looking at the annual average of maximum temperatures, there will be roughly a 2C (about 3.6F) warming in maxima by 2030-2059--think 2045 (click on figures to enlarge).

But by the end of the century (2070-2099, think 2085), the average over the region will be twice that (around 4C increase, about 7F), with considerably more warming in the interior.

What about precipitation?  Looking to the first period (2030-2059), there is a generally small increase in precipitation, but there is something unexpected and subtle---decreases in precipitation in the downstream of some barriers.  An interesting finding to investigate further.

By the end of the century, the precipitation increases are more dramatic.   The Northwest will not dry out under global warming--we will generally get wetter.

Now, let me show you a plot of the annual mean temperatures from all ensemble members at a particular location (in this case Seattle).  Observed temperatures are shown with black dots.

The model runs are reasonably close to the observations before 2018, perhaps a degree too warm.  You will notice a steady rise over the century--nothing abrupt.  It appears that global warming might have contributed about a degree (C) of warming since 1970, with an additional 4C by the end of the century.

Summer precipitation at Seattle?  Lots of variability, but it looks like there will  be a small drying (perhaps 1 inch over the summer) by the end of the century.
Winter precipitation in Seattle?  A small increase, again with lots of year to year variability.

Want to see something scary?  Next, let's look at changes to our snowpack.

Here is the are the April 1 snowpack for 1970-1999, 2030-2049, and 2070-2099.  Modest declines over the lower-elevation terrain by mid-century.  Less change on the high terrain in British Columbia.  Much larger declines by the end of the century.  I don't think there will be skiing in Snoqualmie Pass in 2085 if the warming is not reduced.

Summer winds speed changes at the surface?  Generally weaker, except in the Strait of Juan de Fuca and Strait of Georgia.  Not good for wind generation.

The results I have shown you above are just the tip of the iceberg on what we can explore with these model runs.  Will cloudiness change?  How about the strong winds that drive wildfires?  There are many interesting questions that can be addressed with such climate simulations.

Major Lessons

The runs described above represent the best guidance now available for how global warming will influence our region if nothing is done to address greenhouse gas emissions.   By the end of the century, there will be substantial warming, with the average summer day around Puget Sound climbing into the mid-80s, rather that the upper 70s of today.  Our typical winter day west of the Cascades will have a high around 50F.   Cascades snowpack will decline substantially on April 1st (about 50% below today's value at 5000 ft). Winters will be wetter, but summers slightly drier (they are already typically dry today, but will be even more so under global warming).  Temperatures below freezing will become rare by the end of the century here in Seattle.  East of the Cascades, the influence of warming will be greater (see example for Yakima minimum temperatures below)

We are already seeing some small  temperatures impacts of global warming (1-2F), which implies that the major heat waves  TODAY are mainly natural variability (if temperatures is 20F above normal, as we observed earlier this month, roughly 18F of that warmth is natural).

Next Steps

There is much that should be done next.  First, we need to statistically improve our current runs, using bias correction based on the contemporary period. Next, we should run these simulations with an improved version of our modeling systems, using less aggressive and probably more modest global warming scenarios.  We should run our regional model driven by the next generation of global climate models (CMIP-6) and add physics variability and different start dates to get a wider range of solutions.

Unfortunately, our Amazon funds have been expended....so if you represent a foundation or a potential donor, and are interested in helping, please let me know or check here. 
Change in summer precipitation in inches

I believe simulations like those shown above will provide major assistance to a society that will have to adapt to a certain amount of climate change.  I also think that someone could make a good business out of providing regional climate prediction services.   But this not the kind of thing that the National Science Foundation would support (too applied) and the State of Washington doesn't support much outside climate research.


  1. I appreciate your efforts to get the unbiased scientific info out there Cliff.... day in and day out. It is rare to find this type of information these days, at least without wading thru all the journal articles (which are mostly over my head anyways). Keep up the good work!

  2. Howdy, I am curious about the change we are seeing in the jet stream. Is there any historical information available on the trends of the jet stream. It seems to be heading south more than I can remember. Many of the storms of the mid west and east are happening with the jet stream south in California. How often does it co e off the ocean and are a 90 degree turn down the coast?

    Al Hirsch. al.hirsch@alleyoop.us

  3. As you all can see, Cliff has done a nice job of summarizing the data we have about climate change here. To any who think he overstates the problem, I say: Study the science- and be honest with yourself (something which, I am afraid, many people have trouble doing). To those environmentalists who say he understates the problem, I want to remind you: He's on your side. I know environmentalists don't always agree on tactics. I understand that some activists think we should exaggerate the problem to scare people into moderate action, and in a way, I can understand this. For example, by analogy, many (or most) people, observing that you simmer spaghetti on a medium-low setting (the desired heat), will turn the heat up to high first to get the water boiling, give it a "kick in the pants" to minimize the time, then turn it down. In other words, overdo it at first to get the desired effect sooner. But Cliff takes the position that when it comes to education, one should say it like it is, and I more or less agree even in a case like this. If you exaggerate the problem, as he has said, you risk discrediting yourself, and losing the public following.

    It's unfortunate that science has gotten to be political, but this issue has to be addressed, and we have never faced anything like it before, so there will naturally not always agree on tactics. And yes, it WILL be tough to convert the naysayers. But environmentalists need to work together even when they disagree on tactics.

    1. Seriously,I don't think it is accurate to suggest that "environmentalists" are responsible for politicizing science. Generally speaking, they don't have the political power to do that. There is a lot more political power in the corporate sector, with a lot of players in that sector standing to benefit short-term (meaning in their lifetimes) from convincing folks that human-caused climate change isn't real or significant. We can observe and respond to inaccurate representations of climate science wherever we encounter them, insofar as we are capable. But I am especially concerned when misinformation becomes government or corporate policy.

    2. I'm not singling out the environmental community for politicizing science. People are doing it on both sides. And of course, the government has a responsibility to be honest.

  4. Thanks for all the good information you provide.

  5. What about the chances of extreme events? Are the chances of extreme ARs greater? What about heat waves? If summer averages are in the mid 80s, what do heat waves mean, 100, 110? What about windstorms? More frequent, less frequent, same frequency but lower or higher winds? If there are fewer freezing days, what does that do to insect populations? How will our agriculture be affected? Sure, the averages may go up slowly, but people are affected by the extreme events.
    You make climate change sound pleasant by not mentioning the extremes which are what affect people and property. Those reductions in snowpack mean forest fires and tree mortality events (already happening). AR events or high precipitation events mean more flooding and mudslides (imagine 2007 happening more often). Minimizing the extremes is misleading and gives a false sense of complacency.

  6. Thank you for the clear presentation of your research work. You note that the models are running "perhaps a degree too warm" over the 1970- 2018 period. However, model FGOALS-G2 (the pink line, I believe) appears to match closely the observed Seattle temperatures over the period from 1970 - 2018 and also to have the lowest and very gradual projected temperature increase to 2100. Could you comment on the features of FGOALS-G2 that produce this result and why its results are different from the other models results?

  7. So it sounds like areas of the Westside would have a Csa (hot-summer mediterranean) Koppen climate rather than the Csb (cool-summer mediterranean) experienced now. That checks out with the higher-emissions scenarios contained within this paper:


    Under those same scenarios, Chicago and Boston are projected to shift to a humid subtropical climate (Dfa to Cfa)l Fairbanks to a warm-summer continental (Dfc to Dfb); and subarctic climates would spread to the furthest north reaches of the Arctic Archipelago, where currently only tundra or polar climates can be found. These climate zones are reflective of what vegetation grows in a particular region (Koppen was a botanist)--so we're talking about major shifts in what types of plant communities will grow in a region, taking place at a rapid rate.

    What will this mean? I would guess that some species that predominate in our forests will not survive here by the turn of the next century. And it may take some time for them to get naturally replaced by species found further south. Ecosystems will be in upheaval--especially since this climate zone shifting takes place in addition to all the other stresses that we're putting on the natural world.

  8. Wow! This is the most interesting post I’ve ever come across regarding climate science. I’m biased, of course, being a lifelong Oregonian. Still....so much to think about. Thanks, Cliff.
    (Sorry I gave you a hard time a while back)

  9. Interesting work Cliff. Who exactly is your research group? Is it the Climate Impact Group at UW? I know they (you?) have built regional models like the one you descirbe here, with similar output, for years.

  10. Great work, Cliff!

    Everyone should have the opportunity to know this information. Is it something you can take to the media? It would help a lot of people set realistic expectations for the future. Young people deserve to see the best factual data and interpretation as it becomes available from objective sources.

    Kudos to everyone who contributed!

  11. My 'a little more than anecdotal' observation over the last 70 years is how low it gets at nighttime in the winter. Mud puddles on the driveway in winter time seemed to freeze a lot of nights. Kitsap Lake froze enough that us kids generally made sure we had ice skates that more or less fit.

    Gardening in Lewis county had to assume winter lows of 0-10 degrees F. Sometime in the 90s that all changed to 10-20F, even a bit higher. USDA and Sunset magazine have moved both Seattle and the Inter-mountain areas one climate zone higher, almost all based on expected winter lows.

  12. Thank you for presenting this research. It is helpful to view this careful analysis and recognize we can improve it. To often we try to interpret individual events as caused by climate change. Looking at the long picture, these individual events are not relevant. While this blog deals largely with GHG concentration, precipitation, temperature and therefore snowpack, I wonder if there are ways to suggest the degree and frequency of extreme weather events.

  13. Why did you back test only to 1970? Why not all the way back to when there were records kept in the region?

  14. This is definitely an interesting, preliminary analysis.

    In many ways it sounds like the direct impacts here locally will be relatively minor, compared to other regions of the country and the world. The loss in snowpack is the most concerning, because of that's the source of much of our water and power generation.

    What that means, though, is that we can only expect an increase in population migration to the area, as more and more people are chased out of the southwest and midwest, where the impacts are probably going to be more severe. The resultant stress on all our resources - water, power, waste management, land values and transportation systems will only experience more strain.

    It would be good to get some insight into how public policy intends to address all that.

  15. Have you applied for an AI for Earth grant from Microsoft? They list "Extreme weather and climate modeling" as one of the options for program focus. You can find additional information here - https://www.microsoft.com/en-us/ai/ai-for-earth-grants

  16. Another view as RCP 8.5 as "business as usual" at Judith Curry's blog.

    A closer look at scenario RCP8.5

  17. That seems then like tomatoes will do better here!

  18. I've said this many times previously, but I'll say it again - I'll believe climate change is a crisis when those forever screaming about it start acting like it. There's little talk about real world solutions that are close at hand, such as Thorium reactors. But the environmental groups dismiss this our of hand, so they can keep the grift coming via fundraising and increases taxation

  19. Hi Cliff,

    Long time blog reader. I’m curious as to why you chose a range of -10 to 50 C for your annual mean temperatures in Seattle graph? It seems to leave most of the graph as blank space and seems rather arbitrary as annual mean temperatures in Seattle never approach -10 or 50 C.

  20. Just curious, but are these models still using the global warming theory that was proposed in the Charney Report in 1978 and adopted by the IPCC? In that theory 1/3 of the warming comes from the effects of CO2, and 2/3 from the expected increase in water vapor in the upper troposphere. We can test the CO2 portion empirically and know it to be factual. In the 8 most recent studies I reviewed regarding the water vapor portion, the results of the various experiments were not supporting the contribution of water vapor, because the total precipital water was nowhere near what the theory predicted. Without that portion meeting expectations, warming could increase by 2/3 less than the IPCC theory predicts.

  21. According the Climate of Los Angeles Wikipedia article, the Mean Annual Temperature in Los Angeles today is 18 C. According to the US Climate Data web site the Mean Annual Temperature in Seattle today is 11 C (51.95 F) According to your chart with the black dots it predicts the climate in Seattle in 2100 will be 18 C which is similar to Los Angeles today. That sounds like a 7 C rise in 2100 but you say it would be a 4 C rise. Is that a typo?

  22. Its great to see some regional downscaling to model future conditions more accurately.

    That being said, my concern continues to grow, Cliff, over your predilection to downplay the potential consequences of climate change. In your effort to not sensationalize, you are most definitely over correcting.

    Take for example your highly emphasized statement:
    "So consider what I am about to show as the worst case---and that the actual changes will not be so extreme."

    The worst case scenario is our current trajectory. The only reason you suggest "actual changes will not be so extreme" is a number of unsupported pie in the sky assumptions about vast technological advances that will someday save us from ourselves. I am not so optimistic, and I'm certainly not going to base the interpretation of these important scientific results on assumptions. I certainly would not go as far to suggest, as your statement does, that "its not going to be as bad as we think..."

    I admire your strong commitment to accurate scientific interpretation. Your criticisms of poorly researched media sensationalizing highly nuanced scientific results are well founded, and important to maintain scientific credibility.

    That being said, the language you use to criticize media, and I-1631, and the way you tried to avoid sensationalizing your own work, are over corrections. I have very scientifically literate friends and colleagues, including scientists, who label you (incorrectly) a climate change denier. They are wrong, but the reasons they are upset with you are the same ones I am.

    It appears that you're strongly favoring what amounts to a type 2 error (failing to reject the null hypothesis - i.e. suggesting climate change wont be very significant) to avoid a type 1 error (rejecting the null hypothesis when its true - i.e. suggesting climate change will be very significant when its not). Deciding which error to avoid is a risk assessment exercise.

    The risk you seem to be assessing is the risk to absolute scientific credibility.

    Maybe instead it should be the risk of global catastrophe.

  23. KW

    According to NOAA, Seattle’s annual mean as of 2018 is just over 12C. That matches my eyeball estimate from Cliff’s chart (Black dots). The model ensemble mean (green line) is running about a degree higher, so 13C.

    Looks to me like the green line will be at about 17C by 2100, which is a 4C rise. Maybe subtract a degree back down to match what’s been observed (speculative correction to the model running hot), and Seattle will be about 16C (53.6 F) in 2100, at least according to this study. NOAA does indeed show the Los Angeles annual mean to be 18C. (64.4).

    So still about 11F. cooler than what Los Angeles is now.

  24. Whoops!!
    16C is 60.8F.

    So only about 4F difference between Seattle then and Los Angeles now. Ouch!

  25. I agree with Rebecca Timson. Also, Seattle does not exist in a vacuum. With climate change, food and water shortages will affect everyone, along with epidemics, mass migrations (caused by droughts, wildfires, etc.), and ocean die-offs -- not to mention changing coastlines and other impacts. Mr. Mass presents his predictions as if they are "worst case," but instead they appear to me to be "best case," as he disregards the global context and impact of an entire planet in ecological crisis.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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