Estimation of the anthropogenic aerosol emission effect on the rate of summer warming in Europe

A relationship between aerosol air pollutions and summer air temperatures in Europe was studied. High correlation coefficients between the latitudinal distributions of the zone-averaged trends of the mentioned parameters were found. The potential effects of decrease in the aerosol emission on the cloud optical depth, in the air temperature, and the amount of precipitation in the territory of Europe were estimated on the basis of the obtained regression equations. It was shown that due to the aerosol emission decrease, the average summer temperature in Europe in 2000–2020 could increase by 0.53 °С, which is ~73 % of total summer warming in the region. The empirical estimates obtained in the work were confirmed by the satellite observation data and the numerical calculations of changes in radiation balance components at the top of the atmosphere. It was shown that the radiation emission decrease in the territory of Europe could increase the average radiation balance in Europe in summer months by 2.27 W/m², which is ~65 % of its total change. The increase in the carbon dioxide content in the atmosphere during the same period contributed much less to the observed change in the radiation balance (17.5 %), which supports the hypothesis about the dominant role of aerosols in summer warming in Europe.

Future summer warming pattern under climate change is affected by lapse-rate changes

Greenhouse-gas-driven global temperature change projections exhibit spatial variations, meaning that certain land areas will experience substantially enhanced or reduced surface warming. It is vital to understand enhanced regional warming anomalies as they locally increase heat-related risks to human health and ecosystems. We argue that tropospheric lapse-rate changes play a key role in shaping the future summer warming pattern around the globe in mid-latitudes and the tropics. We present multiple lines of evidence supporting this finding based on idealized simulations over Europe, as well as regional and global climate model ensembles. All simulations consistently show that the vertical distribution of tropospheric summer warming is different in regions characterized by enhanced or reduced surface warming. Enhanced warming is projected where lapse-rate changes are small, implying that the surface and the upper troposphere experience similar warming. On the other hand, strong lapse-rate changes cause a concentration of warming in the upper troposphere and reduced warming near the surface. The varying magnitude of lapse-rate changes is governed by the temperature dependence of the moist-adiabatic lapse rate and the available tropospheric humidity. We conclude that tropospheric temperature changes should be considered along with surface processes when assessing the causes of surface warming patterns.

Regional unevenness of the summer warming in the continental Arctic as an indicator of natural boundaries of northern landscapes

The authors have revealed the features of summer warming in different sectors of the Russian Arctic zone in the modern period and the near future. In connection with the considered features of the summer warming within 1991—2018, the researchers present a unique analysis of the inter-decade distribution of trends in the characteristics of the natural zones surface (vegetation index, total evapotranspiration, surface temperature, albedo). Changes in climatic conditions provide prerequisites for a change in the spectral characteristics of landscape zones, especially in the central sector of the Russian Arctic zone.

Modelling Impacts of Lateral N Flows And Seasonal Warming on an Arctic Footslope Ecosystem N Budget and N2O Emissions Based on Species-Level Responses

Future Arctic tundra primary productivity and vegetation community composition will partly be determined by nitrogen (N) availability in a warmer climate. N mineralization rates are predicted to increase in winter and summer, but because N demand and –mobility varies across seasons, the fate of mineralized N remains uncertain. N mineralized in winter is released in a “pulse” upon snowmelt and soil thaw, with the potential for lateral redistribution in the landscape. In summer, the release is into an active rhizosphere with high local biological N demand. In this study, we investigated the ecosystem sensitivity to increased lateral N input and near-surface warming, respectively and in combination, with a numerical ecosystem model (CoupModel) parameterized to simulate ecosystem biogeochemistry for a tundra heath ecosystem in West Greenland. Both model and measurements indicated that plants were poor utilizers of increased early-season lateral N input, indicating that higher winter N mineralization rates may have limited influence on plant growth and carbon (C) sequestration for a hillslope ecosystem. The model further suggested that, although deciduous shrubs were the plant type with overall most lateral N gain, evergreen shrubs had a comparative advantage utilizing early-season N. In contrast, near-surface summer warming increased plant biomass and N uptake, moving N from soil to plant N pools, and offered an advantage to deciduous plants. Neither simulated high lateral N fluxes nor near-surface soil warming suggests that mesic tundra heaths will be important sources of N2O under warmer conditions. Our work highlights how winter and summer warming may play different roles in tundra ecosystem N and C budgets depending on plant community composition.

Future summer warming pattern under climate change is regulated by lapse-rate changes

Greenhouse gas-driven global temperature change projections exhibit spatial variations, meaning that certain land areas will experience substantially enhanced or reduced surface warming. It is vital to understand enhanced regional warming anomalies as they locally increase heat-related risks to human health and ecosystems. We argue that tropospheric lapse-rate changes play a key role in shaping the future summer warming pattern around the globe in mid-latitudes and the tropics. We present multiple lines of evidence supporting this finding based on idealized simulations over Europe, as well as regional and global climate model ensembles. All simulations consistently show that the vertical distribution of tropospheric summer warming is different in regions characterized by enhanced or reduced surface warming. Enhanced warming is projected where lapse-rate changes are small, implying that the surface and the upper troposphere experience similar warming. On the other hand, strong lapse-rate changes cause a concentration of warming in the upper troposphere and reduced warming near the surface. The varying magnitude of lapse-rate changes is governed by the temperature dependence of the moist-adiabatic lapse rate and the available tropospheric humidity. We conclude that tropospheric temperature changes should be considered along with surface processes when assessing the causes of surface warming patterns.

Towards rainy Arctic winters: experimental icing impacts tundra plant productivity and reproduction

The Arctic is the most rapidly warming region on Earth, but our understanding of ecosystem impacts is still poor. For instance, warming occurs more than twice as fast in winter than in summer, yet long-term tundra vegetation studies have almost exclusively focused on effects of the latter. In winter, more frequent extreme warm spells and associated rain-on-snow events can dramatically alter snowpack conditions and even encapsulate the vegetation in basal ice for several months. Such icing effects on plant phenology, productivity and reproduction remain largely unexplored. We performed a novel five-year-long field experiment in which we simulated every winter a rain-on-snow event resulting in ice encasement of the vegetation, and assessed vascular plant responses in each subsequent growing season. We also tested whether these responses could be modified by summer warming (open top chambers). Icing delayed the dominant shrub`s phenology, in particular early leaf development and seed maturation, increased community-level primary production in the second half of the growing season, but also reduced flower production. These delays and allocation trade-offs were associated with a delay in sub-surface soil thawing and soil warming in spring/summer, conditions known to influence plant root activity and nutrient availability at high latitudes. Interestingly, summer warming mitigated effects of icing alone and the combined treatment showed advanced phenology, increased primary production across the growing season and reduced the negative effects on reproduction. In general, effect sizes of icing were as large as those observed for experimental summer warming alone. The community-level increase in primary production following icing is in sharp contrast with the recently proposed arctic browning effect of extreme winter warm spells in evergreen shrub-dominated tundra communities. Yet, the negative effect on reproductive traits can become critical for species viability if these events become chronic. As we are heading towards a rain-dominated Arctic, our findings highlight the need for coordinated monitoring of the effects of warmer and rainier winters across tundra plant communities and growth forms across the Arctic.