By the year 2100, CIRC research indicates that the Pacific Northwest could be 1 to 8 degrees Celsius (2 to 15 degrees Fahrenheit) warmer than it was during the second half of the twentieth century. These projections come from CIRC’s Integrated Scenarios project, a far-reaching effort to determine what the Pacific Northwest’s climate, hydrology, and vegetation will look like under various warming scenarios projected to occur in this century.
The disparity from 1 to 8 degrees Celsius (2 degrees to 15 degrees Fahrenheit) is due in large part to human choice. We can choose to cut our collective carbon footprint, or we can choose to keep things business as usual. In our research, we represent this choice by using two emissions scenarios: RCP 4.5 and RCP 8.5. (To learn more, see Human Choice, Warming, & Emissions—The Representative Concentration Pathways.) RCP 4.5 assumes humanity starts cutting emissions of CO2 and other greenhouse gases in the coming decades, and hence that temperature increases will start to level off. RCP 8.5, on the other hand, assumes we continue emitting at our current rate with warming continuing to rise and not leveling off.
The other reason for the disparity, or range, in our temperature projections has to do with the scientific community’s fundamental lack of understanding just how the climate system will respond to high levels of greenhouse gases. That’s because while all the relevant physical processes of the Earth’s atmosphere and land are represented in the computer models that climate scientists employ, these models, called global climate models (GCMs), nonetheless represent these physical processes somewhat differently from model to model. The end result is this: each individual model tends to produce different amounts of climate change for the same amount of greenhouse gases. (For details on GCMs, ee Global Climate Models (GCM). This does not mean that the results of GCMs are pie-in-the-sky predictions or simply educated guesses; they’re really well-reasoned, physically-based estimates.
This uncertainty between models is one reason our researchers like to employ multiple GCMs when making climate projections. For instance, temperature results for CIRC’s Integrated Scenarios project sprang from data from some twenty different GCMs combined with two RCPs. This ensemble approach—as well as the degree to which the models and scenarios agreed—means we can say with a high degree of certainty that the Pacific Northwest will be warmer in the future. We just can’t say for certain how much warmer. This high degree of certainty is known in climate research as confidence. As we explain later, this same high degree of confidence does not extend to Precipitation projections for our region.
This graph shows future temperature projections as measured against the historical average, here shown as the dotted, zero line. The information represented here shows the output of some forty simulations, or forty computer-run experiments, showing what our region’s future temperatures are projected to look like under climate change. All the simulations point toward rising temperatures. The question is to what extent. This graph answers this question by representing a range of uncertainty using two warming scenarios RCP 4.5 and RCP 8.5, a medium- and high-warming scenario represented here by yellow and red respectively. (For more info, see Human Choice, Warming, & Emissions—The Representative Concentration Pathways.) Historical temperatures are represented in gray. Keep in mind, this isn’t the actual historical record taken from in-the-field instruments; instead, it represents how the computer models simulated the climate over the historic period, a process called hindcasting that is used to help “train” data from Global Climate Models to statically fit historical observations of our local climate.
Warming Is Already Happening
From 1901 to 2012, average temperatures in the Pacific Northwest increased by roughly 1.3 degrees Fahrenheit (0.7 degrees Celsius), according to an analysis performed by CIRC researchers in 2014. Much of this warming has happened in the last three decades. As of this writing in early 2017, only two years since 1998 have been below the twentieth century average. This means that we have had a nearly unbroken chain of record-breaking, warm years in recent decades. The year 2016 was the most recent “warmest year on record globally.” The previous year—that’s 2015, in case you weren’t paying attention—was also a warmest year on record globally as well as a warmest year on record locally for Oregon, Washington, and Montana, according to data collected by the National Aeronautics and Space Administration (NASA) and National Oceanic and Atmospheric Administration (NOAA). (NOAA is CIRC’s parent organization.)
Image source: “National Overview—Annual 2015,” National Oceanic and Atmospheric Administration National Centers for Environmental Information, accessed December 13, 2016, https://www.ncdc.noaa.gov/sotc/national/201513.
Abatzoglou, John T., David E. Rupp, and Philip W. Mote. "Questionable Evidence of Natural Warming of the Northwestern United States." Proceedings of the National Academy of Sciences 111, no. 52 (2014): E5605-E5606. https://doi.org/10.1073/pnas.1421311112.
Abatzoglou, John T., David E. Rupp, and Philip W. Mote. "Seasonal Climate Variability and Change in the Pacific Northwest of the United States." Journal of Climate 27, no. 5 (2014): 2125-2142. https://doi.org/10.1175/JCLI-D-13-00218.1.
“Integrated Scenarios of the Future Northwest Environment,” University of Idaho, accessed December 13, 2016, http://climate.nkn.uidaho.edu/IntegratedScenarios/.
Rupp, David E., John T. Abatzoglou, Katherine C. Hegewisch, and Philip W. Mote. "Evaluation of CMIP5 20th Century Climate Simulations for the Pacific Northwest USA." Journal of Geophysical Research: Atmospheres 118, no. 19 (2013). https://doi.org/10.1002/jgrd.50843.
“NASA, NOAA Data Show 2016 Warmest Year on Record Globally,” National Aeronautics and Space Administration, accessed January 19, 2017. https://www.nasa.gov/press-release/nasa-noaa-data-show-2016-warmest-year....
“National Overview—Annual 2015,” National Oceanic and Atmospheric Administration National Centers for Environmental Information, accessed December 13, 2016. https://www.ncdc.noaa.gov/sotc/national/201513.