Search

In early studies, northern vegetation response to global warming recognised both increases in biomass/cover and shrinking of species' distributional ranges. Subsequent field measurements focussed on vegetation cover and biomass increases ("greening"), and more recently decreases ("browning"). However, satellite observations show that more than 50% of arctic vegetation has not changed significantly despite rapid warming. While absence of change in remote sensing data does not necessarily mean no ecological change on the ground, the significant proportion of the Arctic that appears to be stable in the face of considerable climate change points to a greater need to understand Arctic ecosystem stability. In this paper, we performed an extensive review of the available literature to seek balances or imbalances between research focussing on "greening", "browning" and "stability/no change". We find that greening studies dominate the literature though two relatively small areas of the Arctic are disproportionately represented for this main change process. Critically, there are too few studies anywhere investigating stability. We highlight the need to understand the mechanisms driving Arctic ecosystem stability, and the potential longer-term consequences of remaining stable in a rapidly changing climate. [ABSTRACT FROM AUTHOR]

The Arctic is rapidly warming posing a significant threat to underlying permafrost. Permafrost degradation has already resulted in extensive damage to the Arctic's built infrastructure, putting communities and industries at risk. Projected climate warming will further reduce the capacity of permafrost to support infrastructure, thereby requiring a rethinking of construction and development of permafrost regions in the future. This paper focuses on three Arctic regions with a substantial presence of population and infrastructure on permafrost: USA (Alaska), Canada, and Russia. The three regions' permafrost construction practices are examined in order to identify best practices and major gaps. We identify a lack of standardized, codified construction guidelines; an absence of permafrost-geotechnical monitoring in communities; barriers to integrating climate scenarios into future planning; limited data sharing; and low numbers of permafrost professionals as major constraints limiting the region's resilience in the face of climate change. Refining building practices and standards, implementing operational permafrost monitoring systems, developing downscaled climate projections, and integrating local knowledge will minimize the impacts of permafrost degradation under rapidly warming climatic conditions. [ABSTRACT FROM AUTHOR]

The Arctic tundra is a relatively young and new type of biome and is especially sensitive to the impacts of global warming. However, little is known about how the Arctic flora was shaped over time. Here we investigate the origin and evolutionary dynamics of the Arctic flora by sampling 32 angiosperm clades that together encompass 3626 species. We show that dispersal into the Arctic and in situ diversification within the Arctic have similar trends through time, initiating at approximately 10–9 Ma, increasing sharply around 2.6 Ma, and peaking around 1.0–0.7 Ma. Additionally, we discover the existence of a long-term dispersal corridor between the Arctic and western North America. Our results suggest that the initiation and diversification of the Arctic flora might have been jointly driven by progressive landscape and climate changes and sea-level fluctuations since the early Late Miocene. These findings have important conservation implications given rapidly changing climate conditions in the Arctic. The Arctic tundra is a relatively young biome. Here, the authors sample 32 angiosperm clades encompassing 3600+ species and find that both long-term dispersal and in situ speciation may have contributed to Arctic flora assembly, in association with landscape, climate and sea-level changes since the early Late Miocene. [ABSTRACT FROM AUTHOR]

In a warming climate, permafrost is likely to be significantly reduced and eventually disappear from the sub-Arctic region. This will affect people at a range of scales, from locally by slumping of buildings and roads, to globally as melting of permafrost will most likely increase the emissions of the powerful greenhouse gas methane, which will further enhance global warming. In order to predict future changes in permafrost, it is crucial to understand what determines the presence or absence of permafrost under current climate conditions, to assess where permafrost is particularly vulnerable to climate change, and to identify where changes are already occurring. The Torneträsk region of northern sub-Arctic Sweden is one area where changes in permafrost have been recorded and where permafrost could be particularly vulnerable to any future climate changes. This paper therefore reviews the various physical, biological, and anthropogenic parameters that determine the presence or absence of permafrost in the Torneträsk region under current climate conditions, so that we can gain an understanding of its current vulnerability and potential future responses to climate change. A patchy permafrost distribution as found in the Torneträsk region is not random, but a consequence of site-specific factors that control the microclimate and hence the surface and subsurface temperature. It is also a product of past as well as current processes. In sub-Arctic areas such as northern Sweden, it is mainly the physical parameters, e.g., topography, soil type, and climate (in particular snow depth), that determine permafrost distribution. Even though humans have been present in the study area for centuries, their impacts on permafrost distribution can more or less be neglected at the catchment level. Because ongoing climate warming is projected to continue and lead to an increased snow cover, the permafrost in the region will most likely disappear within decades, at least at lower elevations. [ABSTRACT FROM AUTHOR]

Quantitative estimates of the relationship between interannual variations in the extent of Antarctic and Arctic sea ice and changes in the surface air temperature in the Northern and Southern hemispheres are obtained using satellite, ground-based, and reanalysis data for the past four decades (1980–2019). It is shown that the previously noted general increase in the extent of Antarctic sea ice observed until recent years from satellite data (available only since the late 1970s) over the background global warming and a rapid decrease in the extent of Arctic sea ice is associated with a regional decrease in the surface temperature at Antarctic latitudes from the end of the 1970s. This is a result of regional manifestation of natural climate variations with periods of up to several decades against the background of global secular warming with a relatively weak temperature trend over the ocean in the Southern Hemisphere. Since 2016, a sharp decrease in the extent of Antarctic sea ice in the Southern Ocean has been observed. The results of the correlation and cross-wavelet analysis indicate significant coherence and negative correlation with the surface temperature of the extent of sea ice in recent decades, not only in the Arctic, but also in the Antarctic. [ABSTRACT FROM AUTHOR]

Temperatures were examined at 118 stations located in the Arctic and compared to observations at 50 European stations whose records averaged 200 years and in a few cases extend to the early 1700s. Nearly all stations exhibited warming trends. For each station, the temperature relative to the average value during 1961-1990 was found. The resulting temperature change averaged over the Arctic stations was plotted. For the period 1820-2014, trends were found for the January, July and annual temperatures of 1.0, 0.0 and 0.7 °C per century, respectively. Decadal variations are evident and much of the temperature increase occurred during the 1990s. Over the past century, Siberia, Alaska and Western Canada have experienced somewhat greater warming than Eastern Canada, Greenland and Northern Europe. The temperature change experienced by the Arctic stations during the last two centuries closely tracks that found for the European stations. [ABSTRACT FROM AUTHOR]

Tundra vegetation is responding rapidly to on-going climate warming. The changes in plant abundance and chemistry might have cascading effects on tundra food webs, but an integrated understanding of how the responses vary between habitats and across environmental gradients is lacking. We assessed responses in plant abundance and plant chemistry to warmer climate, both at species and community levels, in two different habitats. We used a long-term and multisite warming (OTC) experiment in the Scandinavian forest-tundra ecotone to investigate (i) changes in plant community composition and (ii) responses in foliar nitrogen, phosphorus, and carbon-based secondary compound concentrations in two dominant evergreen dwarf-shrubs ( Empetrum hermaphroditum and Vaccinium vitis-idaea) and two deciduous shrubs ( Vaccinium myrtillus and Betula nana). We found that initial plant community composition, and the functional traits of these plants, will determine the responsiveness of the community composition, and thus community traits, to experimental warming. Although changes in plant chemistry within species were minor, alterations in plant community composition drive changes in community-level nutrient concentrations. In view of projected climate change, our results suggest that plant abundance will increase in the future, but nutrient concentrations in the tundra field layer vegetation will decrease. These effects are large enough to have knock-on consequences for major ecosystem processes like herbivory and nutrient cycling. The reduced food quality could lead to weaker trophic cascades and weaker top down control of plant community biomass and composition in the future. However, the opposite effects in forest indicate that these changes might be obscured by advancing treeline forests. [ABSTRACT FROM AUTHOR]

The Arctic land area has warmed by >1 °C in the last 30 years and there is evidence that this has led to increased productivity and stature of tundra vegetation and reduced albedo, effecting a positive (amplifying) feedback to climate warming. We applied an individual-based dynamic vegetation model over the Arctic forced by observed climate and atmospheric CO for 1980-2006. Averaged over the study area, the model simulated increases in primary production and leaf area index, and an increasing representation of shrubs and trees in vegetation. The main underlying mechanism was a warming-driven increase in growing season length, enhancing the production of shrubs and trees to the detriment of shaded ground-level vegetation. The simulated vegetation changes were estimated to correspond to a 1.75 % decline in snow-season albedo. Implications for modelling future climate impacts on Arctic ecosystems and for the incorporation of biogeophysical feedback mechanisms in Arctic system models are discussed. [ABSTRACT FROM AUTHOR]

Climate warming will induce changes in Arctic ecosystem carbon balance, but besides climate, nitrogen availability is a critical controlling factor of carbon cycling. It is therefore essential to obtain knowledge on the influence of a changing climate on nitrogen fixation, as this process is the main source of new nitrogen to arctic ecosystems. In order to gain information on future nitrogen fixation rates in a changing climate, we studied the effects of two decades of warming with passive greenhouses, shading with sackcloth, and fertilization with NPK fertilizer on nitrogen fixation rates. To expand the knowledge on species-specific responses, we measured nitrogen fixation associated with two moss species: Hylocomium splendens and Aulacomnium turgidum. Our expectations of decreased nitrogen fixation rates in the fertilizer and shading treatments were met. However, contrary to our expectation of increased nitrogen fixation in the warming treatment, we observed either no change ( Hylocomium) or a decrease ( Aulacomnium) in fixation in the warmed plots. We hypothesize that this could be due to moss-specific responses or to long-term induced effects of the warming. For example, we observed that the soil temperature increase induced by the warming treatment was low and insignificant as vegetation height and total vascular plant cover of the warmed plots increased, and moss cover decreased. Hence, truly long-term studies lasting more than two decades provide insights on changes in key biogeochemical processes, which differ from more transient responses to warming in the Arctic. [ABSTRACT FROM AUTHOR]

There is widespread concern that anthropogenic global warming will trigger Arctic climate tipping points. The Arctic has a long history of natural, abrupt climate changes, which together with current observations and model projections, can help us to identify which parts of the Arctic climate system might pass future tipping points. Here the climate tipping points are defined, noting that not all of them involve bifurcations leading to irreversible change. Past abrupt climate changes in the Arctic are briefly reviewed. Then, the current behaviour of a range of Arctic systems is summarised. Looking ahead, a range of potential tipping phenomena are described. This leads to a revised and expanded list of potential Arctic climate tipping elements, whose likelihood is assessed, in terms of how much warming will be required to tip them. Finally, the available responses are considered, especially the prospects for avoiding Arctic climate tipping points. [ABSTRACT FROM AUTHOR]

Greening of the Arctic due to climate warming may provide herbivores with richer food supplies, resulting in higher herbivore densities. In turn, this may cause changes in vegetation composition and ecosystem function. In 1982-1984, we studied the ecology of non-breeding moulting geese in Jameson Land, low Arctic East Greenland. By then, geese consumed most of the graminoid production in available moss fens, and it appeared that the geese had filled up the available habitat. In 2008, we revisited the area and found that the number of moulting geese and the temperature sum for June-July had tripled, while the above-ground biomass in a moss fen ungrazed by geese had more than doubled. In a goose-grazed fen, the overall plant composition was unchanged, but the frequency of graminoids had decreased and the area with dead vegetation and open spots had increased. We suggest that climate warming has lead to increased productivity, allowing for higher numbers of moulting geese. However, the reduction of vegetation cover by grazing may have longer term negative consequences for the number of geese the habitat can sustain. [ABSTRACT FROM AUTHOR]

Presents a study of the acclimation of ecosystem carbon dioxide exchange in the Alaskan Arctic region in response to decadal climate warming. Thoughts on the effect of continued warming of the ecosystem; Methods; Impact that the warming has on such things as the changes in nutrient cycling, physiological acclimation, and population and community reorganization; Results; Conclusions.