Pipelines are critical infrastructure for Yakutia, transporting vital supplies to communities in this vast northern region. The pipeline routes in central Yakutia traverse areas of ice-rich permafrost that is sensitive to temperature changes. This study examined the thermal state of permafrost in undisturbed and disturbed settings along the Lena River to Mundulakh Reservoir water pipeline and the Mastakh to Yakutsk gas pipeline and considered the effects of climatic fluctuations and surface disturbances (forest removal and wildfire) over the monitoring periods of 28 and 18 years, respectively. The geocryological conditions in the study area, as well as the methods of permafrost thermal monitoring, are described. The observation results demonstrated significant increases in the mean annual ground temperature in the upper permafrost layers, as well as in the active-layer thickness following fire and post-fire clearing. At some sites, progressive deepening of the active layer caused the formation of taliks and reached the top of massive ground ice, initiating permafrost degradation. The development of extreme ground temperatures in the layer of annual temperature fluctuations was analyzed according to the combination of seasonal and annual meteorological conditions and the type of anthropogenic impact. The research results can be extrapolated to similar anthropogenic landscapes.

Thermokarst depressions are widespread phenomena due to permafrost degradation in the Arctic, whereas only few are known from mountain permafrost of the mid-latitudes. In the Italian Central Alps, close to the Stelvio Pass (2,763 m above sea level), a ski run was built in 1987. Since 1981, statistically significant air warming has been recorded, especially during summer (+0.65 degrees C per decade). Permafrost temperature recorded at the nearby Share Stelvio Borehole between 1990 and 2011 exhibited a rapid increase (> 0.8 degrees C per decade) and an active-layer thickening (7 cm/year). Between the years 1999 and 2003, some thermokarst depressions started to develop, initially in the lower part of the ski run and then extending to higher elevations. The depressions increased in number, size, and depth with time. Since ski-run construction, the area remained free of vegetation until early 2000, when vegetation colonization started, showing a coupling with the onset of thermokarst development and summer warming. Vegetation changes accelerated with the ingress of pioneer and early-successional as well as of late-successional species. Moreover, the ingress of shrub species (Salix spp.) typical of lower elevation belts (subalpine and even montane) was dated to 2004. All the observed features show a rapid and coupled response of the abiotic and biotic components of this ecosystem to climate warming. Our data also confirm the similarity of the observed responses and dynamics of the alpine tundra with the Arctic tundra with regard to both permafrost and vegetation.

Anthropogenic aerosols partially mask the greenhouse warming and cause the reduction in Asian summer monsoon precipitation and circulation. By decomposing the atmospheric change into the direct atmospheric response to radiative forcing and sea surface temperature (SST)-mediated change, the physical mechanisms for anthropogenic-aerosol-induced changes in the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM) are diagnosed. Using coupled and atmospheric general circulation models, this study shows that the aerosol-induced troposphere cooling over Asian land regions generates anomalous sinking motion between 20 degrees and 40 degrees N and weakens the EASM north of 20 degrees N without SST change. The decreased EASM precipitation and the attendant wind changes are largely due to this direct atmospheric response to radiative forcing, although the aerosol-induced North Pacific SST cooling also contributes. The SST-mediated change dominates the aerosol-induced SASM response, with contributions from both the north-south interhemispheric SST gradient and the local SST cooling pattern over the tropical Indian Ocean. Specifically, with large meridional gradient, the zonal-mean SST cooling pattern is most important for the Asian summer monsoon response to anthropogenic aerosol forcing, resulting in a reorganization of the regional meridional atmospheric overturning circulation. While uncertainty in aerosol radiative forcing has been emphasized in the literature, our results show that the intermodel spread is as large in the SST effect on summer monsoon rainfall, calling for more research into the ocean-atmosphere coupling.

Global warming as quantified by surface air temperature has been shown to be approximately linearly related to cumulative emissions of CO2. Here, a coupled state-of-the-art Earth system model with an interactive carbon cycle (BNU-ESM) was used to investigate whether this proportionality extends to the complex Earth system model and to examine the climate system responses to different emission pathways with a common emission budget of man-made CO2. These new simulations show that, relative to the lower emissions earlier and higher emissions later (LH) scenario, the amount of carbon sequestration by the land and the ocean will be larger and Earth will experience earlier warming of climate under the higher emissions earlier and lower emissions later (HL) scenario. The processes within the atmosphere, land, and cryosphere, which are highly sensitive to climate, show a relatively linear relationship to cumulative CO2 emissions and will attain similar states under both scenarios, mainly because of the negative feedback between the radiative forcing and ocean heat uptake. However, the processes with larger internal inertias depend on both the CO2 emissions scenarios and the emission budget, such as ocean warming and sea level rise.

Previous studies on the response of the South Asian summer monsoon to the direct radiative forcing caused by anthropogenic absorbing aerosols have emphasized the role of premonsoonal aerosol forcing. This study examines the roles of aerosol forcing in both pre- and postonset periods using the Community Earth System Model, version 1.0.4, with the Community Atmosphere Model, version 4. Simulations were perturbed by model-derived radiative forcing applied (i) only during the premonsoonal period (May-June), (ii) only during the monsoonal period (July-August), and (iii) throughout both periods. Soil water storage is found to retain the effects of premonsoonal forcing into succeeding months, resulting in monsoonal central India drying. Monsoonal forcing is found to dry all of India through local responses. Large-scale responses, such as the meridional rotation of monsoon jet during June and its weakening during July-August, are significant only when aerosol forcing is present throughout both premonsoonal and monsoonal periods. Monsoon responses to premonsoonal forcing by the model-derived realistic distribution versus a uniform wide-area distribution were compared. Both simulations exhibit central India drying in June. June precipitation over northwestern India (increase) and southwestern India (decrease) is significantly changed under realistic but not under wide-area forcing. Finally, the same aerosol forcing is found to dry or moisten the July-August period following the warm or cool phase of the simulations' ENSO-like internal variability. The selection of years used for analysis may affect the precipitation response obtained, but the overall effect seems to be an increase in rainfall variance over northwest and southwest India.

Making use of the extensive shipboard and aircraft measurements of aerosol properties over the oceanic regions surrounding the Indian peninsula, under the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) field experiment during the premonsoon season (March-May), supplemented with long-term satellite data and chemical transport model simulations, investigations are made of the east-west and north-south gradients in aerosol properties and estimated radiative forcing, over the oceans around India. An eastward gradient has been noticed in most of the aerosol parameters that persisted both within the marine atmospheric boundary layer and above up to an altitude of similar to 6 km; the gradients being steeper at higher altitudes. It was also noticed that the north-south gradient has contrasting patterns over the Bay of Bengal and the Arabian Sea on the either side of the Indian peninsula. The aerosol-induced atmospheric heating rate increased from a low value of 0.1 K day(-1) in the southwestern Arabian Sea to as high as similar to 0.5 K day(-1) over the northeastern Bay of Bengal. The simulations of species-resolved spatial gradients have revealed that the observed gradients are the result of the strong modulations by anthropogenic species over the natural gradients, thereby emphasizing the role of human activities in imparting regional forcing. These large spatial gradients in aerosol forcing induced by mostly anthropogenic aerosols over the oceanic regions around the Indian peninsula can potentially affect the regional circulation patterns.

The direct radiative effect of absorbing aerosols consists of absorption-induced atmospheric heating together with scattering- and absorption-induced surface cooling. It is thus important to understand whether some of the reported climate impacts of anthropogenic absorbing aerosols are mainly due to the coexistence of these two opposite effects and to what extent the nonlinearity raised from such coexistence would become a critical factor. To answer these questions specifically regarding the South Asia summer monsoon with focus on aerosol-induced changes in monsoon onset, a set of century-long simulations using the Community Earth System Model, version 1.0.3 (CESM 1.0.3), of NCAR with fully coupled atmosphere and ocean components was conducted. Prescribed direct heating to the atmosphere and cooling to the surface were applied in the simulations over the Indian subcontinent, either alone or combined, during the aerosol-laden months of May and June. Over many places in the Indian subcontinent, the nonlinear effect dominates in the changes of subcloud layer moist static energy, precipitation, and monsoon onset. The surface cooling effect of aerosols appears to shift anomalous precipitative cooling away from the aerosol-forcing region and hence turn the negative feedback to aerosol-induced atmospheric heating into a positive feedback on the monsoon circulation through latent heat release over the Himalayan foothills. Moisture processes form the critical chain mediating local aerosol direct effects and onset changes in the monsoon system.

In the present work it is investigated the direct shortwave effect of anthropogenic aerosols on the near surface temperature over Southeastern Europe and the atmospheric circulation during summer 2000. In summer 2000, a severe heat-wave and droughts affected many countries in the Balkans. The study is based on two yearly simulations with and without the aerosol feedback of the regional climate model RegCM3 coupled with a simplified aerosol model. The surface radiative forcing associated with the anthropogenic aerosols is negative throughout the European domain with the more negative values in Central and Central-eastern Europe. A basic pattern of the aerosol induced changes in air temperature at the lower troposphere is a decrease over Southeastern Europe and the Balkan Peninsula (up to about 1.2 degrees C) thus weakening the pattern of the climatic temperature anomalies of summer 2000. The aerosol induced changes in air temperature from the lower troposphere to upper troposphere are not correlated with the respective pattern of the surface radiative forcing implying the complexity of the mechanisms linking the aerosol radiative forcing with the induced atmospheric changes through dynamical feedbacks of aerosols on atmospheric circulation. Investigation of the aerosol induced changes in the circulation indicates a southward shift of the subtropical jet stream playing a dominant role for the decrease in near surface air temperature over Southeastern Europe and the Balkan Peninsula. The southward shift of the jet exit region over the Balkan Peninsula causes a relative increase of the upward motion at the northern flank of the jet exit region, a relative increase of clouds, less solar radiation absorbed at the surface and hence relative cooler air temperatures in the lower troposphere between 45 degrees N and 50 degrees N. The southward extension of the lower troposphere aerosol induced negative temperature changes in the latitudinal band 35 degrees N-45 degrees N over the Balkan Peninsula is justified from the prevailing northerly flow advecting the relatively cooler air from the latitudinal band 45 degrees N-50 degrees N towards the lower latitudes. The present regional climate modeling study indicates the important role of anthropogenic aerosols for the regional climate and their dynamical feedback on atmospheric circulation.