The core insight is deceptively simple. Solar radiation does not fall evenly across a landscape. A north-facing slope in the Northern Hemisphere receives less direct beam radiation than a south-facing one; steep gullies sit in shadow for much of the day; and the interplay of slope, aspect and solar geometry produces a patchwork of microclimates that can differ by many degrees within a few dozen meters. Ecologists have long recognized these topoclimates as potential refugia, but most large-scale models of species’ responses to climate change still rely on coarse climate surfaces that smooth this heterogeneity away. Adams and Riddell set out to quantify what that smoothing costs in biological terms, using a mechanistic framework that translates the physical environment into the currency that ultimately matters for survival: energy.

The technical machinery behind the study is considerable. The researchers assembled climate and elevation data from WorldClim version 2.1, slope information from the EarthEnv topography dataset, mountain range delineations from the Global Mountain Biodiversity Assessment Mountain Inventory version 2, and soil properties from SoilGrids 2.0, validating their soil temperature predictions against empirical records from the Soil Climate Analysis Network. On top of these layers they built solar radiation calculations that account for the position of the sun through the day and the year, the tilt and orientation of every grid cell, and the shading cast by surrounding terrain. The result is a continental-scale map of the actual radiative environment experienced at the ground surface across North American mountains, rather than the idealized flat-plate irradiance that standard climate rasters imply.

Into this physical landscape they placed two model organisms that sit at opposite ends of the activity spectrum. The western fence lizard, Sceloporus occidentalis, is a diurnal ectotherm whose body temperature, metabolism and foraging opportunities are governed by the sun. The southern Appalachian salamander Plethodon metcalfi, by contrast, is nocturnal and lungless, active when the sun is down and constrained as much by moisture as by heat. Using bioenergetic models of the kind increasingly favored in biophysical ecology, the team simulated annual energy expenditure and activity budgets for both animals under current and future climate conditions, first without topographic shading and then with it included. The difference between those two runs is the study’s central measurement: the biological value of a shadow.

For the diurnal lizard, that value proved enormous. Incorporating topographic shading reduced predicted annual energy expenditure by up to 20.8 percent, a margin comparable to some of the direct physiological costs of warming itself. More striking still, shading increased the buffering benefit of shifting elevation by 82.1 percent. In other words, when an animal can move both uphill and into shaded aspects, the terrain multiplies the relief it obtains from warming. A lizard that simply climbs a mountain gains the adiabatic cooling of altitude; a lizard that also settles on a cool, shaded slope gains a second, terrain-driven discount on its thermal burden. Models that ignore shading therefore systematically underestimate the refuge value of complex mountains for daytime ectotherms, and may misjudge which populations can persist without range shifts at all.

The nocturnal salamander told a different story. Because it is active at night, when direct solar radiation has vanished and air temperatures converge across aspects, topographic shading provided little buffering of its thermal environment. This asymmetry carries a sobering implication: the same mountain that functions as a climate refuge for a sun-basking lizard may offer a nocturnal, moisture-dependent animal almost no protection at all. Conservation strategies that treat topographic complexity as a universal buffer may be protecting some species while leaving others exposed. The study’s extended analyses also showed that shading produces aspect-specific shifts in the timing of activity and metabolic cost across the hours of the day and the months of the year, meaning terrain reshapes not just how much energy an animal spends but when in the daily and seasonal cycle those costs fall.

Elevation itself emerged as a sharpening fault line. Warming increased energetic costs most at low elevations, widening the gap between the energetic lives of lowland and highland populations. Under future conditions, metabolic expenditure declined more steeply with elevation than it does today for both species, while activity patterns diverged: the lizard’s activity decreased with elevation, whereas the salamander’s increased. The practical consequence is that climate change is not merely pushing thermal stress upward in a uniform wave; it is intensifying the energetic stratification of mountains, concentrating the worst cost-of-living pressures on the low-elevation margins where many species already live near their physiological limits.

Perhaps the most geopolitically resonant finding is continental in scope. Across North America, the researchers found that 48.9 percent of mountain ranges are depleted in the topographic features that buffer the effects of warming. Whether a range can offer its residents shaded refugia is not an accident of the moment but a legacy of deep time: tectonic history shapes present-day terrain-driven microclimates. Ranges forged by different geological processes carry different endowments of steep slopes, contrasting aspects and shadowed valleys. Two mountains with identical summit elevations and identical climate projections can therefore present entirely different futures to the animals living on them. This reframes mountain biodiversity vulnerability as a problem in geology as much as climatology, and suggests that global vulnerability maps built on elevation alone miss half the story.

The study arrives amid a broader correction in climate-change ecology. Earlier work has shown that microclimatic buffering reduces extinction risk, that forest canopies cool the air beneath them by several degrees globally, and that microclimates can slow or even redirect the velocity of climate change through tropical forests. Field studies have repeatedly documented that organisms partition themselves between north- and south-facing slopes, from reptiles and arthropods to salamanders and rodents. What Adams and Riddell add is a quantitative, continent-wide translation of that heterogeneity into energy budgets, the physiological ledger that connects environment to fitness. Recent work on desert lizards has described a cost-of-living squeeze under warming; this study shows that the squeeze is partly negotiable, and that the terms of the negotiation are written into the bedrock.

The implications ripple outward in several directions. For species distribution models, the message is that shading is not a refinement but a first-order variable for diurnal ectotherms, and that omitting it can bias predictions of range shifts, refugia and extinction risk in ways that are now measurable. For conservation planners, the results argue for prioritizing rugged, topographically diverse landscapes, and for recognizing that nearly half of North America’s mountain ranges lack the terrain features that would let shading do its protective work. The authors’ data and code are openly available through Zenodo, inviting other researchers to extend the approach to endotherms, to other continents and to finer spatial scales. As warming accelerates, the study suggests that the fate of mountain life may depend not only on how high the mercury climbs, but on where the shadows fall.

Subject of Research: How topographic shading and terrain-driven microclimates mediate the energetic and physiological responses of ectotherms to climate warming across North American mountain landscapes

Article Title: Topographic variation shapes organismal responses across mountain landscapes

Article References: Adams, D. R., & Riddell, E. A. (2026). Topographic variation shapes organismal responses across mountain landscapes. Nature Climate Change. https://doi.org/10.1038/s41558-026-02773-z

Image Credits: AI Generated

DOI: 10.1038/s41558-026-02773-z

Keywords: topographic shading, microclimate, mountain ecology, climate change, ectotherms, bioenergetic modelling, elevation, solar radiation, lizards, salamanders, refugia, tectonic history