Observations from the main mountain climate station network in the western United States (U.S.) suggest that higher elevations are warming faster than lower elevations. This has led to the assumption that elevation-dependent warming is prevalent throughout the region with impacts to water resources and ecosystem services. Here we critically evaluate this network's temperature observations and show that extreme warming observed at higher elevations is the result of systematic artifacts and not climatic conditions. With artifacts removed, the network's 1991-2012 minimum temperature trend decreases from +1.16°C decade À1 to +0.106°C decade À1 and is statistically indistinguishable from lower elevation trends. Moreover, longer-term widely used gridded climate products propagate the spurious temperature trend, thereby amplifying 1981-2012 western U.S. elevation-dependent warming by +217 to +562%. In the context of a warming climate, this artificial amplification of mountain climate trends has likely compromised our ability to accurately attribute climate change impacts across the mountainous western U.S.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. INSTAAR, University of Colorado andThe Regents of the University of Colorado, a body corporate, contracting on behalf of the University of Colorado at Boulder for the benefit of INSTAAR are collaborating with JSTOR to digitize, preserve and extend access to Arctic, Antarctic, and Alpine Research. IntroductionAccurate, high-resolution soil-surface temperature fields are vital for modeling many ecosystem interactions, over a wide range of spatial and temporal scales. Despite the importance of soil-surface temperature to many ecological, hydrological, geomorphological, and climatological investigations, instrumental networks report air temperature at screen height almost exclusively. Relatively few soil temperatures data sets have been obtained from a wide variety of land-cover types. This lack of information presents difficulties for ecologists, soil scientists, physical geographers, and geocryologists. Microenvironmental studies of plant physiology (Arft et al., 1999; Mueller et al., 1999), animal populations (Peach et al., 1994; Reid and Krebs, 1996), soil climate (Halliwell et al., 1990; Goulden et al., 1998), freeze/thaw depths (Nelson et al., 1997), trace-gas fluxes (Vourlitis et al., 1993), and geomorphic studies (Sellmann et al., 1975), for example, could benefit from detailed information about soil-surface temperatures.However intuitive a relationship between air and soil temperatures may appear, these thermal regimes can be very different, depending on the properties of the ground surface. One method for addressing this problem is to estimate soil-surface temperature from air temperature, a standard meteorological measurement. The n-factor (Carlson, 1952) is the ratio of seasonal degree-day sums at the soil-surface to those in the air at standard screen height. This index has been used for construction and engineering purposes in the Arctic since World War II (Hildebrand, 1983), but applications in natural landscapes have remained largely conceptual until recently, owing to difficulties involved with obtaining the large numbers of measurements needed for any but a few homogenous, engineered surfaces. Recent advances in data-logger technology provide the means by which to record and store thousands of temperature observations Abstract The n-factor, or ratio of the seasonal degree-day sum at the soil surface to that in the air at standard screen height, has been used for more than 40 yr in engineering studies to parameterize the temperature regime at the ground surface. Conceptually, this index represents the complex energy balance at the surface as a single dimensionless number and has applications in ecology, climatology, and geocryology. Although the n-factor has been use...

The relationship between large fire occurrence and drought has important implications for fire prediction under current and future climates. This study’s primary objective was to evaluate correlations between drought and fire-danger-rating indices representing short- and long-term drought, to determine which had the strongest relationships with large fire occurrence at the scale of the western United States during the years 1984–2008. We combined 4–8-km gridded drought and fire-danger-rating indices with information on fires greater than 404.7ha (1000acres). To account for differences in indices across climate and vegetation assemblages, indices were converted to percentile conditions for each pixel. Correlations between area burned and short-term indices Energy Release Component and monthly precipitation percentile were strong (R2=0.92 and 0.89), as were correlations between number of fires and these indices (R2=0.94 and 0.93). As the period of time tabulated by indices lengthened, correlations with fire occurrence weakened: Palmer Drought Severity Index and 24-month Standardised Precipitation Index percentile showed weak correlations with area burned (R2=0.25 and –0.01) and number of large fires (R2=0.3 and 0.01). These results indicate associations between short-term indices and moisture content of dead fuels, the primary carriers of surface fire.

The village of Barrow, Alaska, is the northernmost settlement in the USA and the largest native community in the Arctic. The population has grown from about 300 residents in 1900 to more than 4600 in 2000. In recent decades, a general increase of mean annual and mean winter air temperature has been recorded near the centre of the village, and a concurrent trend of progressively earlier snowmelt in the village has been documented. Satellite observations and data from a nearby climate observatory indicate a corresponding but much weaker snowmelt trend in the surrounding regions of relatively undisturbed tundra. Because the region is underlain by ice-rich permafrost, there is concern that early snowmelt will increase the thickness of the thawed layer in summer and threaten the structural stability of roads, buildings, and pipelines. Here, we demonstrate the existence of a strong urban heat island (UHI) during winter. Data loggers (54) were installed in the ∼150 km 2 study area to monitor hourly air and soil temperature, and daily spatial averages were calculated using the six or seven warmest and coldest sites. During winter (December 2001-March 2002, the urban area averaged 2.2°C warmer than the hinterland. The strength of the UHI increased as the wind velocity decreased, reaching an average value of 3.2°C under calm (<2 m s −1 ) conditions and maximum single-day magnitude of 6°C. UHI magnitude generally increased with decreasing air temperature in winter, reflecting the input of anthropogenic heat to maintain interior building temperatures. On a daily basis, the UHI reached its peak intensity in the late evening and early morning. There was a strong positive relation between monthly UHI magnitude and natural gas production/use. Integrated over the period September-May, there was a 9% reduction in accumulated freezing degree days in the urban area. The evidence suggests that urbanization has contributed to early snowmelt in the village.

In some regions underlain by ice‐rich permafrost, a consistent, long‐term increase in ALT under changing climatic conditions is not supported by observations. The apparent lack of ALT may be attributed to soil consolidation from thawing of the uppermost ice‐rich permafrost and subsidence of the ground surface. Four plots established in 1962 at Barrow, Alaska, were re‐instrumented in 2003 and surveyed annually using differential GPS technology, accompanied by active‐layer probing. Elevation change from 1962 to 2003 was within the interannual variability of the 2003–15 period, indicating net stability in the area. Over the 2003–15 period, however, all four plots experienced subsidence trends of 0.4–1.0 cm/year, resulting in a net elevation change of 8–15 cm. Warmer winters and increased snow depth during this period decreased the potential for frost heave. Warmer summers resulted in thaw penetration into the ice‐rich transient layer and ice wedges, leading to the net subsidence in recent years. Copyright © 2016 John Wiley & Sons, Ltd.