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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. [ABSTRACT FROM AUTHOR]

Quantitative estimates of the contribution of anthropogenic forcing, characterized by changes in the radiative forcing of greenhouse gases in the atmosphere, and key modes of natural climatic variability to the surface temperature trends in different latitudinal zones of the Northern (NH) and Southern Hemisphere (SH) for various time horizons have been obtained using observational data. In particular, using three-component autoregressive models and data since the 19th century, the role of the Atlantic Multidecadal Oscillation, the El-Niño/Southern Oscillation, the Pacific Decadal Oscillation, the Interdecadal Pacific Oscillation, and the Antarctic Oscillation in the formation of temperature trends was assessed. The results of the analysis indicate the significant role of changes in the radiative forcing of greenhouse gases in the atmosphere in the formation of the global surface air temperature trend, which increases with an increase in the time horizon. At the same time, significant differences were noted for the latitudinal zones of the SH and NH, associated with the influence of different modes of natural climatic variability. At weaker temperature trends in the SH latitudinal zones with greater ocean coverage than in the NH, negative trends in the surface air temperature on intervals of several decades against the general background of long-period global warming be and are manifested due to natural climate fluctuations. One of the key climatic problems of recent years is the mutually opposite trends in the extent of Antarctic and Arctic sea ice, which is associated with the noted global and regional features of the temperature variations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Changes in the frequency and intensity of atmospheric severe convective events, including heavy rainfall, thunderstorm, hailstorm, squall, and tornado, in the Russian regions during the warm season are analyzed using different independent sources of information. Based on observations at Russian weather stations in 1966–2020, the frequency of thunderstorm, hailstorm, and strong wind, the contribution of extreme showers to total precipitation, and the cumulonimbus cloud fraction are estimated. Based on satellite data, the frequency and intensity of tornado and squall events that caused windthrows for 1986–2021 and the height of the top of deep convective clouds for 2002–2021 are also evaluated. The ERA5 reanalysis data are used to analyze the frequency of conditions favorable for the development of moderate and intense severe convective events in 1979–2020. The results indicate a general intensification of severe convective events in most Russian regions, except for a number of regions in the south of the European part of Russia. The frequency of moderate hazards has a decreasing trend, and the frequency of the most intense severe hazards has an increasing trend. It is reasonable to take the results into account when developing plans for the adaptation of Russian regions and industries to climate change. [ABSTRACT FROM AUTHOR]

Contributions of the anthropogenic influence characterized by variations in the atmospheric greenhouse gas radiative forcing and of the key modes of natural climate variability to the trends of surface air temperatures at different latitudes of the Southern Hemisphere on different temporal horizons are quantified from observations. The role of the Atlantic Multidecadal Oscillation, El Niño/Southern Oscillation, Interdecadal Pacific Oscillation, and Antarctic Oscillation in driving these temperature trends is estimated using trivariate autoregressive models and data since the 19th century. We note the substantial contributions of the key modes of natural climate variability to temperature trends on rather short intervals of about two or three decades, which is comparable to or even greater than the contribution of greenhouse gases. The estimates characterizing polar, middle, and tropical latitudes of the Southern Hemisphere are compared with those obtained for the Northern Hemisphere. According to these estimates, a dominant contribution to temperature trends at different latitudes and for the Earth as a whole on the intervals of about half a century and longer is made by the radiative forcing of greenhouse gases in the atmosphere. [ABSTRACT FROM AUTHOR]