The results of an analysis of temperature variations in the mesopause region based on long-term measurements of hydroxyl airglow at the Zvenigorod Scientific Station of the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (ZSS IAP RAS) during 1960–2024 against the global-scale climate changes are presented. Along with temperature variations in the mesopause region, two versions of temperature variations in the mesopause region, normalized to the same level of solar activity, were analyzed. Quantitative estimates of a significant decrease in temperature in the mesopause region over the past decades in winter, against the background of global surface temperature increases, were obtained. Additionally, using cross-wavelet analysis of data for the time interval 1960–2024, significant coherence of their most long-term variations with the surface temperature in the Northern Hemisphere was noted, which had not been observed in data for shorter time intervals. The possibility of such coherence was predicted in (Mokhov et al., 2017) in the context of continued global warming based on the results of model simulations for the 20th–21st centuries, taking into account anthropogenic forcing, but it had not been observed in obsevational data for shorter time intervals. Along with long-term trends, notable features include a sharp temperature drop in the mesopause region during the 1970s and its synchronicity with the well-known shift in surface climate regimes associated with El Niño events. The results of cross-wavelet analysis using data obtained at ZSS IAP RAS for the time interval 1960–2024 indicate a more significant connection between temperature variations in the mesopause region and El Niño indices in recent decades.

This study investigates seasonal changes in near-surface wind speeds in the Arctic using the regional climate model (RCM) simulations with RCA4 driven by four global climate models (GCMs) CMIP5 under Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios. In addition, the RCM RCA-GUESS (RCA4 with interactive vegetation dynamics) is used to investigate the role of biogeophysical feedbacks in modulating near-surface wind speeds under different RCP scenarios. Our results show that the reduction in ocean surface roughness induced by sea-ice reduction leads to a projected increase in near-surface wind speeds over the Arctic Ocean, with the most pronounced effects occurring in autumn and winter. Overall, the projected changes in near-surface wind speeds from the RCM are consistent with the changes from the forcing GCMs though the RCM simulations show larger amplitude changes compared to the GCMs. The expansion of vegetation on land increases surface roughness and alters atmospheric circulation by modifying static stability and the land-sea temperature contrast, leading to changes in near-surface wind speeds. Specifically, wind speeds decrease over continental regions but increase over parts of the Arctic Ocean. This study emphasizes that interactive vegetation dynamics significantly influence changes in land surface properties and near-surface wind speeds. These processes should be incorporated into Earth system models to enhance the accuracy of future climate projections.

The analysis is carried out for changes in runoff of the Amur and Selenga rivers in the 21st century according to the CMIP6 (Coupled Model Intercomparison Project, Phase 6) climate model ensemble simulations using the Bayesian approach versus stream gage data on annual runoff and GPCP-2.3 dataset on annual precipitation over catchments on different timescales. For both catchments, significant intermodel differences are associated with the projections of multiyear mean runoff and interannual variability. The intermodel distribution of Bayesian weights indicates a high role of uncertainty related to initial conditions for model simulations. There is a positive trend in total runoff in the Amur River basin in the 21st century under all analyzed anthropogenic forcing scenarios. For total runoff of the Selenga River, there are no trends in the 21st century for all analyzed scenarios. No significant trends for the Amur and Selenga surface runoff were revealed for all algorithms for considering Bayesian weights and all anthropogenic forcing scenarios. At the same time, significant interdecadal variations in the interannual variability of runoff were found.

The results of an analysis of temperature variations in the mesopause region based on long-term measurements of hydroxyl airglow at the Zvenigorod Scientific Station of the A.M. Obukhov Institute of Atmospheric Physics RAS (ZSS IAP RAS) in 1960-2024 in comparison with variations of surface temperature characterizing global-scale climate changes are presented. Along with temperature variations in the mesopause region, two versions of temperature variations in the mesopause region, normalized to the same level of solar activity, were analyzed. Quantitative estimates of a strong decrease in temperature in the mesopause region over the past decades in winter against the background of a global increase in surface temperature have been obtained. It was noted that significant coherence of long-term variations for temperature in the mesopause region with the surface temperature in the Northern Hemisphere with the use of cross-wavelet analysis, what was not previously evident in data for a shorter time interval. The possibility of such coherence was predicted in (Mokhov et al., 2017) under the continuation of global warming based on the results of model simulations for the 20-21 centuries, taking into account anthropogenic forcing. It was not previously manifested from observational data for a shorter time interval. Along with long-term trends, features of a sharp decrease in temperature in the mesopause region in the 1970s with its synchronicity with the known shift in surface climate regimes associated with El Niño events were analyzed. The results of cross-wavelet analysis using data obtained at the ZSS IAP RAS for the time interval 1960-2024 indicate a more significant connection between temperature variations in the mesopause region and El Nino indices in recent decades.

The characteristic temporal scales of response of the globally averaged climate model with the carbon cycle to external influences with the analysis of the spectrum of the linearized evolution operator of the corresponding dynamical system are evaluated. The model exhibits response time scales of about 4–6 years (related to the carbon dynamics in vegetation) and in the range of 20–100 years (related to the carbon dynamics in non-humified soil reservoirs). When taking into account the effect of humification in the model reveals the time scale of the response, which is on the order of several millennia. For the closed carbon cycle, a time scale of 102 years is revealed, which characterizes the joint changes in the atmospheric and ocean reservoirs. At high universality of the proposed approach it can be used for a wide range of tasks.

Based on the ERA5 reanalysis data for the period 1979-2021, the authors have quantified the seasonal and regional connections between significant wave heights and changes in cyclone activity in the atmosphere of the Northern Hemisphere. The contribution of extratropical cyclones to the formation of the corresponding features and variations of sea waves is evaluated. The maxima of the extreme sea wave occurrence frequency in winter and summer corresponds to sea areas with an increased frequency of cyclones, in particular, over the Pacific and Atlantic oceans. It has been found that the contribution of extratropical cyclones to the generation of significant wave heights reaches 70% in winter and 50% in summer. The largest contribution is associated with intense cyclones: 90% in winter and 40% in summer.

The natural fluxes of CO2 and CH4 into the atmosphere from the territory of Russia in the 21st century have been analyzed using the results of simulations with the ensemble of global climate models of the international CMIP6 project. Estimates of natural CO2 fluxes in Russian regions differ greatly for different models. Their values for the beginning of the 21st century range from –1 to 1 GtC/year. In the 21st century, the differences in model estimates of fluxes are growing, and, at the end of the 21st century, in the scenario with the largest anthropogenic impacts, SSP5-8.5 range from –2.5 to 2.5 GtC/year. Estimates of natural methane emissions to the atmosphere from the territory of Russia also differ greatly for different models. Modern methane emissions are estimated in the range from 10 to 35 MtCH4/year, with an increase in the 21st century of up to 300

Quantitative estimates of the contributions of the anthropogenic forcing, characterized by changes in the radiative forcing of atmospheric greenhouse gases (CO2, in particular), and solar activity variations to the trends of the global surface temperature on secular temporal horizons are obtained with the aid of autoregressive models from simulations with climate models of the CMIP6 ensemble and from long-term observational data since the 19th century. The results for the simulations with climate models characterized by low, medium and high temperature sensitivity to changes in the CO2 content are compared. It is found, in particular, that the estimates from observation data revealing the determinative contribution of the CO2 content to the global surface temperature trends on half-century and century-long time intervals are most consistent with the estimates from simulations with the climate model with the lowest sensitivity of the global surface temperature to doubling the CO2 atmospheric content.

The predictability of climate anomalies in the regions of Northern Eurasia in connection with El Nino phenomena is analyzed. Particular attention is paid to the most likely transition in 2024 from an El Nino phase at the beginning of the year to a La Nina phase at the end of the year, with the greatest probability of high temperatures and dry conditions in European Russia during the spring and summer months, as in 2010. The predictability levels of regional climate anomalies using different El Nino indices are compared. The relationship of the noted seasonal anomalies with atmospheric blockings is considered, taking into account the different phases of the key modes of climate variability like El Nino phenomena and the Pacific Decadal Oscillation. Changes in the predictability of regional climate anomalies under global climate change are discussed.

The results of an analysis of changes in the characteristics of atmospheric centers of action (ACAs) in the Northern (NH) and Southern (SH) hemispheres using results of simulations with the CMIP5 and CMIP6 ensembles of climate models are presented. The ability of models to simulate ACA features is estimated for the historical scenario in comparison with ERA5 reanalysis data. The projected changes are evaluated under RCP8.5 and SSP5-8.5 scenarios for CMIP5 and CMIP6 models, respectively. The ACA intensity is evaluated that defined as the difference in sea level pressure averaged over the ACA region and the entire hemisphere. In NH, reanalysis and models show greater intensity of subtropical oceanic anticyclonic ACAs in summer than in winter. The opposite is found for the intensity of NH subpolar oceanic cyclonic ACAs. The interannual variability of the ACA intensity in winter is generally greater than in summer. In SH, the season with greater intensity of oceanic anticyclonic and cyclonic ACAs and its interannual variability varies from ocean to ocean. CMIP5 and CMIP6 models show substantial changes of ACAs characteristics in the XXI century. More significant trends in the strengthening of ACAs in the 21st century appear in the SH, especially in the winter seasons. The most consistent weakening trends are found over continents for winter North American maximum and the summer Asian minimum. For the winter Siberian maximum, the weakening trend is found more pronounced in CMIP6 models than in CMIP5.

The changes in the frequency of severe weather events and their seasonal features in Russian regions are analyzed using the data for 1998-2021. More than 2/5 of severe weather events are observed in summer, which is also characterized by the greatest increase in the frequency in the recent decades: by almost 1.5 times, with an increase of 1 K in the Northern Hemisphere surface air temperature. The frequency of extreme events also significantly increases in spring, while the minimum relative increase was found for winter. Significant changes have been identified: in the recent years, there has been at least one severe weather event per day averagely and two to three such events per day in summer. Correlation of the detected trends (in particular, a more significant increase in the frequency of severe weather events in summer months) with the changes in the temperature stratification and moisture capacity of the atmosphere and the intensification of convective processes in the atmosphere under warming has been found. Against the background of the general increasing trend in the frequency of extreme weather events, some features associated with key modes of climate variability (these peculiarities are manifested, in particular, in the atmospheric blocking patterns) are noted in the recent decades.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070085

We obtained quantitative estimates of the spatial and seasonal features of the characteristics of anticyclones in the atmosphere of the Northern Hemisphere and their changes in recent decades using the ERA5 reanalysis data (1979–2021). A high correlation between the interannual variations of the mean seasonal recurrence of anticyclones and surface temperature over extensive regions in the extratropical latitudes of the Northern Hemisphere was noted. According to the obtained estimates, up to 60% of the interannual variance of surface temperature in winter and summer is associated with variations of the mean seasonal recurrence of anticyclones, and up to 50% with variations of intense winter and summer anticyclones.

The results of a comparative analysis of various characteristics of the temperature conditions of the planetary atmospheres in the Solar System and their dependence on orbital parameters, in particular on the length and angular frequency of the annual cycle, are presented. A root dependence on the angular frequency of the dry adiabatic lapse rate is noted. The dependence of the planetary equilibrium temperature in the form of the cubic root of the angular frequency of the annual cycle is related to Kepler’s third law. For Venus, Earth, Mars, Jupiter, and Saturn, the root dependence of the scale height and the troposphere height on the annual cycle length is manifested, and the atmospheric features of the most distant planets from the Sun—Uranus and Neptune—are noted.

The phase shifts between the global surface temperature T and the carbon dioxide content in the atmosphere q obtained in numerical experiments with models of the Earth’s climate system under the CMIP6 project (Coupled Models Intercomparison Project, phase 6) for the period of 1850–2014 have been analyzed. According to the study results, the sign of the phase shift between q and T depends not only on the time interval analyzed, but also on the processing method of the initial series. The initial q series (with a filtered annual cycle) is ahead in phase with the corresponding T series for most models and time intervals. The first differences (inter-monthly increments) of the q series lag in phase behind the corresponding first differences of the T series by about ten months with an adequate reproduction of the results obtained by analyzing the observation data over recent decades. It means that such a delay should not be an argument against the generally accepted global warming theory related to the current increase in temperature to the dominant influence of anthropogenic greenhouse gas emissions into the atmosphere.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070085

Regional anomalies in the frequency of atmospheric blockings in the Northern Hemisphere detected on the basis of reanalysis data since 1979 during different phase transitions of El Niño phenomena in different phases of the Pacific Decadal and Atlantic Multidecadal Oscillations are estimated—in particular, the regional frequency of summer blockings associated with extreme phases of El Niño phenomena and transitions between them. Significant differences are noted for the El Niño phenomena detected with the use of different indices characterizing different process types.

Contributions of the insolation variations together with different natural and anthropogenic factors to the trends of the surface air temperatures at different latitudes of the Northern and Southern Hemispheres on various temporal horizons are estimated from climate data since the nineteenth century with the use of empirical autoregressive models. As the natural climate variability modes, we take into account Atlantic Multidecadal Oscillation, El-Nino/Southern Oscillation, Interdecadal Pacific Oscillation, Pacific Decadal Oscillation, and Antarctic Oscillation. According to the obtained results, the contributions of the insolation variations to the trends of the surface air temperature are statistically insignificant on the time intervals under study, i.e. from a decade and longer. Taking into account the insolation variations in the autoregressive models weakly alters the estimates of the contributions of the greenhouse gases and natural variability modes to the temperature trends: the changes are not more than several per cent. Numerically, the estimated contributions of the insolation variations can considerably exceed the respective contributions of the natural variability modes both on short (less than two decades) and long (longer than a century) time intervals.

A comparative analysis of mutual changes in temperature and aerosol content in the atmosphere was carried out by the data of Antarctic ice cores obtained at the Russian Vostok station and within the framework of the international EPICA project for the past 800,000 years. According to the results of cross-wavelet analysis for the last hundreds of thousands of years, variations in the content of aerosol in the atmosphere, as well as in the content of greenhouse gases CO2 and CH4, are generally lagging relative to temperature changes for the glacial cycles that dominated within the past million years with periods of about 100 thousands years associated with change in the eccentricity of the Earth’s orbit around the Sun. At the same time, for shorter-term glacial cycles, opposite effects appear at certain time intervals with a delay in temperature variations relative to variations in the content of radiatively active components in the atmosphere, including marine and continental (dust) aerosol . In particular, the delay of temperature variations with respect to variations in the content of aerosol in the atmosphere (as well as with respect to variations in the content of methane in the atmosphere) manifests itself for modes associated with the obliquity changes with periods of about 40 thousands years.

Changes in the snow cover extent S in Eurasia have been analyzed using the results of simulations with an ensemble of global climate models of the CMIP6 international project under the SSP2-4.5 scenario of anthropogenic impacts for the 21st century. Features of S variability in relation to changes in surface air temperature T in different seasons are revealed by comparing ensemble model calculations for the historical scenario to CDR satellite data against the background of a general decrease in the snow cover extent in Eurasia during contemporary warming. It is noted that the multimodel ensemble mean estimates of the sensitivity parameter dS/dT for the transitional seasons in spring and autumn can be significantly lower in absolute values than those for the individual models and those derived from satellite data. A comparison of model estimates with satellite observation data has shown that the models generally reproduce the observations from the snow cover area in Eurasia, while variations in the area may be underestimated for individual models. According to ensemble model calculations, the rate of snow cover reduction in Eurasia in the second half of the 21st century decreases when compared to the first half of the 21st century for all seasons. At the same time, the maximum values of the rate of reduction of snow cover extent in Eurasia are inherent in transitional seasons (autumn and spring).