The incorporation of climate refugia concepts in large-scale protection efforts (e.g., 30% protected by 2030, 50% by 2050) is needed to forestall the global extinction crisis. The 8.19 M ha Northern Rockies Ecoregion (NRE) of western Montana, northeastern Washington, and northern Idaho, USA, includes the 159,822 Yaak River Watershed (YRW) in northwest Montana, a proposed climate refugium that may buffer extreme climate change effects. Climate projections show temperature increases along with reduced summer precipitation, lowered spring snowpack, and increased wildfire susceptibility across the NRE but to a lesser extent in the YRE under an intermediate emissions scenario. Overall protection levels were quite low in the NRE (2.2% in GAP 1 or 2) and even lower in the YRW (1% of national forests; the USDA Forest Service manages most of the area). Approximately 32% of forests are mature but only 2.4% and 0.25% are protected (GAP 1 or 2) within the NRE and YRW, respectively. Habitat protection levels for eight focal forest species selected to reflect conservation priorities were generally low, with only wolverine (Gulo gulo) meeting conservation targets if roadless areas were better protected. Most (~75%) Forest Service fuel reduction treatments were >1 km from structures despite congressional funds aimed at the wildland–urban interface/intermix. Increased roadless area protections would close the lower bound (30%) target for most ecosystem types and focal species but still fall short of upper targets. We recommend coupling conservation targets with strategic investments in fuel reductions aimed at the innermost buffer around structures, while reducing logging and roadbuilding in priority areas and refugia.

Global climate models often simulate atmospheric conditions incorrectly due to their coarse grid resolution, flaws in their dynamics, and biases resulting from parameterization schemes. Here we document a bias in the magnitude and extent of minimum temperature extremes in the CMIP6 model ensemble, relative to ERA5. The bias is present in the southern Cascadia region (i.e., Pacific Northwestern United States and southwestern British Columbia, Canada, spanning from the coast to the Rocky Mountains), with some models showing a bias magnitude in excess of −10°C in the first percentile of daily winter minimum temperature. The sea level pressure pattern for these events is similar in CMIP6 models and ERA5, showing high anomalies in the Northeast Pacific that are indicative of an atmospheric blocking pattern and consequently more northerly flow. Though this atmospheric blocking pattern is typically concurrent with cold winter temperatures across much of North America, Rocky and Cascade mountain ranges prevent the cold air from reaching the southern Cascadia region as confirmed by the observations and reanalysis. Our results suggest that the bias in CMIP6 minimum temperatures is a result of unresolved topography in the Rockies and Cascade mountain ranges, such that the terrain does not adequately block cold air advection from reaching the southern Cascadia region.

The 8.19M ha Northern Rockies Ecoregion (NRE) of western Montana, northeastern Washington, and northern Idaho, USA, includes the 159,822 Yaak River Watershed (YRW) in northwest Montana, a proposed climate refugium. Regional climate projections show the NRE heating up, experiencing reduced summer precipitation, lowered spring snowpack, and increased wildfires, especially under a very high emissions pathway. Large-scale conservation proposals have stalled for decades, in part, due to the lack of an integrated approach to conservation target setting (e.g., 30% protected by 2030, 50% by 2050) that simultaneously addresses climate change planning and especially wildfire risk reduction. We conducted a comprehensive ecoregional conservation assessment that showed overall protection levels were quite low in the NRE (2.2% in GAP 1 or 2) and even lower in the YRW (1% of national forests, the USDA Forest Service manages most of the area). Approximately 32% of NRE forests are mature but only 2.4% is protected (GAP 1 or 2) with just 0.25% of mature forests protected within the YRW. Of the 8 focal forest species examined, habitat protection for all of them were well-below conservation targets with only wolverine (Gulo gulo) meeting the targets if roadless areas were better protected. Most (~75%) Forest Service fuel reduction treatments were >1 km from structures despite congressional funds aimed at the wildland-urban interface/intermix. Increased roadless area protections would close the lower bound (30%) conservation target for most ecosystem types, mature forests, and focal species but fall short of higher targets. We recommend coupling conservation targets with strategic investments in fuel reductions aimed at the innermost buffer around structures, while reducing logging and roadbuilding in priority areas.

Persistent, multi-year shifts in atmospheric circulations and their associated influence on regional climates have profound impacts on physical, biological, and socioeconomic systems. The Pacific Decadal Precession (PDP), an atmospheric mode of variability consisting of a lower tropospheric height dipole which rotates counterclockwise over several years in the North Pacific, describes a series of such shifts in atmospheric circulations. One phase of the PDP, the north-south (N-S) phase, is hypothesized to be partially driven by central tropical Pacific (CP) sea surface temperature (SST) variability, but robust assessment of this dynamical connection in climate models remains to be done. In this study, we investigate this hypothesis with analyses in both reanalysis and selected models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) archive. We show that the emergence of the N-S phase is both related to and influenced by tropical Pacific decadal SST variability, specifically variability associated with CP El Niño-Southern Oscillation (ENSO) events. When examining the CMIP6 model output, we find that most models cannot recover the characteristic cyclonic precession of the dipoles of the PDP, instead featuring only amplitude and sign changes of the N-S phase, Moreover, the models do not replicate the dynamical connections between the tropical Pacific and this North Pacific mode. Our results suggest that primary reasons for this inconsistency are that models inaccurately simulate both the SST pattern associated with the PDP, shared low-frequency power associated with CP ENSO events, and incorrect Rossby wavetrains emanating from the tropical Pacific into the North Pacific on quasi-decadal timescales. Taken together, our analyses offer another benchmark by which to test the fidelity of the climate model simulations in capturing Pacific decadal climate variability in order to improve decadal-to-centennial climate projections.

Global climate models often simulate atmospheric conditions incorrectly due to their coarse grid resolution, flaws in their dynamics, and biases resulting from parameterization schemes. Here we document the magnitude and extent of minimum temperature biases in the CMIP6 model ensemble, relative to ERA5. Bias in the southern Cascadia region (i.e. Pacific Northwestern United States and southwestern British Columbia, Canada, spanning from the coast to the Rocky Mountains) stands out relative to the rest of North America, with some models showing a bias in excess of -10°C in the 1st percentile of daily winter minimum temperature. During the coldest minimum temperature days, the CMIP6 models show an anomalous high in mean sea level pressure in the Northeast Pacific – an atmospheric blocking pattern that is also present in ERA5. While this atmospheric blocking pattern is typically concurrent with cold temperatures across much of North America, terrain barriers such as the Rockies and Cascades prevent the cold air from reaching the Pacific Northwest in observation and reanalysis. Our results suggest that the bias in CMIP6 minimum temperatures is a result of unresolved topography in the Rockies and Cascade mountain ranges, such that the terrain does not adequately block cold air advection from the interior of the continent.