Regional Climate Projections

How is climate projected to change in the Northwest?

The visualization below shows projected changes in temperature and precipitation for 2 future time periods in 3 regions in the Pacific NW.

How to use this tool

  • Use the tab at the top to select which variable you want to consider: Temperature, or Precipitation.
  • The buttons to the right can be used to select:
    • the region you want to look at (Pacific Northwest, West of the Cascades, or East of the Cascades),
    • the future time period of interest: 2050s (2040-2069), and 2080s (2070-2099), and
    • the season (annual, fall, winter, spring, summer).
  • This type of plot is called a “box & whisker” plot. For this figure, the line in the shaded box shows the median value, and the bottom and top of the box show the 25th and 75th percentiles, and the “whiskers” show the minimum and maximum values.
    • The 4 bars show the results for four different scenarios of future greenhouse gas emissions (called “Representative Concentration Pathways”, or RCPs).
  • The greenhouse gas scenarios span from a very low scenario (RCP 2.6), that assumes rapid reductions in greenhouse gas emissions, to a high scenario (RCP 8.5), which assumes continued increases in emissions through the end of the 21st century.
  • The individual colored dots show the results for each of the global models for which data were available (about 30 models, on average, for each scenario).
  • All results are shown as the change relative to the 1950-1999 average.

Background Information

What is a Global Climate Model?

Global climate models (GCMs) simulate the interactions between the atmosphere, ocean and land to project future climate, based on assumptions about future emissions of greenhouse gases. Among other things, these models estimate future changes in temperature and precipitation.

Greenhouse Gas Scenarios

Greenhouse gas scenarios are formed by inputting possible future emissions, population growth, technological advances etc to give 4 scenarios. The most recent scenarios are called RCPs (Representative Concentration Pathways). Greenhouse gases, via the greenhouse effect, warm the planet by trapping energy that would otherwise be emitted to space. The number following each RCP relates to the magnitude of that heat-trapping effect: it corresponds to the amount of energy, in watts per square meter (W/m2), that is absorbed by the earth’s climate by the year 2100. If future greenhouse gas emissions decrease rapidly over the coming decades, this energy imbalance could be as low as 2.6 W/m2 by 2100 (RCP 2.6). Alternatively, if emissions continue to accelerate, this could reach 8.5 W/m2 by 2100.

Global Climate Model (GCM) Projections

Projecting future climate requires making assumptions about future greenhouse gas emissions and then modeling the climate’s response to those emissions. The most recent effort to combine the efforts of international modeling centers is called the Coupled Model Intercomparison Project, Phase 5 (CMIP5). This is a freely-available public archive of climate model simulations from several dozen modeling groups. These groups produced simulations using the same set of greenhouse gas scenarios, along with other common assumptions which allow for the comparison of projections across all models and scenarios. Since no climate model is perfect, we can use the range among models as an estimate of the uncertainty in model projections of the future. Read more about climate models on the CMIP5 site.

Comparing New and Old Projections

The CMIP5 experiment is the latest set of global model projections. Many previous climate impacts assessments in the Pacific Northwest are based on the previous CMIP3 GCM projections. The newer CMIP5 projections are very similar to those of the older CMIP3 models — most of the differences are due to different assumptions about future greenhouse gas emissions. A comparison of the two is shown below.

cmip3 vs cmip5

Comparison of CMIP3 vs CMIP5

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