The emergence of novel ecosystems caused by glacier retreat and anthropogenic climate change is one of the fastest environmental changes observed on Earth, with considerable ecological and societal cascading consequences.
However, while July 2023 was recorded as the Earth's warmest month on record, and glacier funerals are becoming common events for glaciologists, the collection of field data in glacier forelands (i.e., the landscapes emerging after glacier retreat) is still sporadic and often gathered in only a handful of sites. Particularly, we lack detailed microclimatic information at a global scale, which is needed to fully assess the impact of warming on the novel proglacial ecosystems. Our research has shown that soil microclimates vary highly in space and time and although it is tightly linked to broadscale conditions, the velocity of warming also decouples from the global trends, calling attention to a need for high-resolution data produced at a global scale.
Biodiversity loss, freshwater scarcity, and increasing natural hazards and risks are the greatest socio-ecological challenges associated with glacier shrinkage worldwide. Understanding how microclimates and snow cover vary across the landscapes and how they modulate the emerging ecosystems, and their biodiversity, will help scientists to better forecast the future of these novel landscapes and improve their conservation and management. Indeed, recent studies have highlighted the role of proglacial ecosystems as refuges for cold-adapted biota and as land that favors primary productivity (i.e., carbon sink) and generalist species, and have called for their in-situ protection.
This study is the result of intensive fieldwork, with innumerable hours spent, and hundreds of kilometers hiked at the foot of 26 glacier forelands, burying temperature sensors, and downloading data in sometimes extreme conditions. The forelands are in the Svalbard archipelago (Norway; 2 forelands), the European Alps (Italy, Austria, Switzerland, and France; 21 forelands), and the Andes (Peru; 3 forelands). Between July 2011 and August 2021, we collected soil temperature data from a total of 175 stations spread across multiple mountain chains. Carrying out fieldwork in such environments is highly challenging —though exhilarating— because of the remoteness, extreme climatic conditions, and elevation (as high as 4910 m.a.s.l), among other factors; therefore, the generated data set of 706,801 temperature records is unique of its kind, and as far as we know it is the most complete collection of soil temperature recordings in proglacial areas.
The integrated analysis of empirically-calibrated relationships with processed-based models enabled us to generate high-resolution, global reconstruction of monthly average soil temperatures during the snow-free season, assess microclimate changes from 2001 to 2020, and provide estimates of the global-scale buffering effects of microclimates.
We found that temporal changes in microclimates are tightly linked to regional or global climate trends, with macroclimate playing the major role in driving local temperatures. Our results highlighted a generalized increase in soil temperature from 2001 to 2020. This temperature increase, however, was particularly marked in the Inter-tropical zone and Southern hemisphere, with a generally higher increase nearby glaciers. The accelerated warming of such areas is likely linked to the shrinkage of ice, with the consequent reduction of its cooling effect, and to the prolongation of the snow-free season that we globally observed. The accelerated warming in glacier forelands will amplify temperature increases along elevational gradients, thus generating major impacts on the whole ecosystem such as the alteration of biotic communities and ecosystem productivity.
Nonetheless, the impact of increasing soil temperatures and duration of snow-free season on local alpine biota may be partially counterbalanced by the spatial variability of microclimate conditions. Our estimation of the potential for microclimatic buffering revealed that current spatial variability is one-to-ten times larger than the temporal temperature changes experienced in the last 20 years. Such spatial variability in microclimate conditions has key effects on local communities and might allow individuals and even communities to withstand, at least temporarily, the effects of climate warming by modifying their distribution over relatively short distances.
Nevertheless, such buffering effect is unlikely to be enough, if we do not act immediately to reduce the rate of global warming, as several climate change scenarios predict an increase of approximately >4 °C by the end of the century in most of the mountain regions.
As a product of this study, we also provide an open-access script that can allow the reconstruction at very high resolution (up to 30 m) of soil temperature in any mountain chain of the world.
In summary, our analysis of high mountain and glacier foreland soil temperatures found that although temporal changes in microclimate are tightly linked to broad-scale climatic patterns, the rate of local warming shows great spatial heterogeneity, with faster warming nearby glaciers and during the warm season, and an extension of the snow-free season. This knowledge can help us understand the relationships between mountain species and their environment, as well as quantify their responses to climate change, to guide targeted conservation efforts for novel proglacial ecosystems in the face of climate change and biodiversity loss.