Changes in the climate and sea ice of the Northern Hemisphere in the 20th and 21st centuries from data of observations and modeling

The shrinking of the area occupied by sea ice in the Northern Hemisphere accelerated at the end of the 1990s, when the record minima of the summer area were successively noted, and its absolute minimum was observed in September 2007. Such a radical decrease is ahead of the projections of global models and provokes interest in the reliability of model calculations of the future of Arctic sea ice. The results of an analysis of the relation between the warming in the Arctic and the ice extent shrinkage from data of observations and modeling by an ensemble of global climate models are presented.     

Regional structure of surface-air temperature fluctuations in northern Eurasia in the latter half of the 20th and early 21st centuries

The first empirical orthogonal functions (EOF1s) of surface-air temperature fluctuations for Russia and its neighboring states within the period 1950–2005 are analyzed. The spatial distribution of the EOF1, the first principal components (PC1s) of the observed air temperature (averaged over the summer, July, December–March, and individual winter months), and their time variations (including trend parameters, some spectral characteristics, and the quantitative indices of relation to circulation indices (on the basis of multiple step-by-step regression)) are considered. Significant seasonal differences have been revealed: the winter air-temperature fluctuations are characterized by a higher (when compared to summer) spatial coherence, especially in the latitudinal direction. The EOF1 of the winter air temperature (averaged over December–March) describes its fluctuations for almost all of Russia; in this case, no less than 70% of the PC1 variability is due to variations in several circulation indices; the main contribution (60%) is made by both the North Atlantic Oscillation (NAO) and Scandinavian (SCAND) indices. On the whole, over the periods 1951–2005 and 1971–2005, the NAO contribution exceeds the SCAND contribution to the winter temperature variability; the NAO is associated with a more rapid increase in air temperature in 1968–1997 and with the 1971–2005 trend. In 1951–1970 the main contribution to air temperature fluctuations was made by SCAND; the SCAND contribution exceeds the NAO contribution in the periods 1951–2005 and 1971–2005. The 1971–2005 and 1968–1997 temperature trends are completely described by variations in the NAO (70%) and SCAND (30%) indices for January and February.     

Modeling the evolution of the world ocean ice cover in the 20th and 21st centuries

The current state of the simulation of sea ice cover as a component of new-generation global climate models is considered. Results from the model ensemble simulation of the observed world ocean ice cover, including its evolution in the 20th century, are analyzed, and projection of possible changes in the 21st century for three scenarios of anthropogenic forcing of the climate system are described. Unresolved problems and priorities for sea ice modeling are discussed.     

Sea ice evolution over the 20th and 21st centuries as simulated by current AOGCMs

Outputs from simulations performed with current atmosphere-ocean general circulation models for the Fourth Assessment Report of Intergovernmental Panel on Climate Change (IPCC AR4) are used to investigate the evolution of sea ice over the 20th and 21st centuries. We first use the results from the “Climate of the 20th Century Experiment” to assess the ability of these models to reproduce the observed sea ice cover changes over the periods 1981–2000 and 1951–2000. The projected sea ice changes over the 21st century in response to the IPCC Special Report on Emission Scenarios A1B are then examined. Overall, there is a large uncertainty in simulating the present-day sea ice coverage and thickness and in predicting sea ice changes in both hemispheres. Over the period 1981–2000, we find that the multimodel average sea ice extent agrees reasonably well with observations in both hemipsheres despite the wide differences between the models. The largest uncertainties appear in the Southern Hemisphere. The climate change projections over the 21st century reveal that the annual mean sea ice extent decreases at similar rates in both hemispheres, and that the reduction in annual mean sea ice volume is about twice that of sea ice extent reduction in the Northern Hemisphere, in agreement with earlier studies. We show that the amplitude of the seasonal cycle of sea ice extent increases in both hemispheres in a warming climate, with a larger magnitude in the Northern Hemisphere. Furthermore, it appears that the seasonal cycle of ice extent is more affected than the one of ice volume. By the end of the 21st century, half of the model population displays an ice-free Arctic Ocean in late summer.     

Climate and carbon cycle variations in the 20th and 21st centuries in a model of intermediate complexity

The climate model of intermediate complexity developed at the Oboukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS CM), has been supplemented by a zero-dimensional carbon cycle model. With the carbon dioxide emissions prescribed for the second half of the 19th century and for the 20th century, the model satisfactorily reproduces characteristics of the carbon cycle over this period. However, with continued anthropogenic CO₂ emissions (SRES scenarios A1B, A2, B1, and B2), the climate-carbon cycle feedback in the model leads to an additional atmospheric CO₂ increase (in comparison with the case where the influence of climate changes on the carbon exchange between the atmosphere and the underlying surface is disregarded). This additional increase is varied in the range 67–90 ppmv depending on the scenario and is mainly due to the dynamics of soil carbon storage. The climate-carbon cycle feedback parameter varies nonmonotonically with time. Positions of its extremes separate characteristic periods of the change in the intensity of anthropogenic emissions and of climate variations. By the end of the 21st century, depending on the emission scenario, the carbon dioxide concentration is expected to increase to 615–875 ppmv and the global temperature will rise by 2.4–3.4 K relative to the preindustrial value. In the 20th–21st centuries, a general growth of the buildup of carbon dioxide in the atmosphere and ocean and its reduction in terrestrial ecosystems can be expected. In general, by the end of the 21st century, the more aggressive emission scenarios are characterized by a smaller climate-carbon cycle feedback parameter, a lower sensitivity of climate to a single increase in the atmospheric concentration of carbon dioxide, a larger fraction of anthropogenic emissions stored in the atmosphere and the ocean, and a smaller fraction of emissions in terrestrial ecosystems.     

Simulation of climate changes in the 20th–22nd centuries with a coupled atmosphere-ocean general circulation model

The results of numerical experiments with a coupled atmosphere-ocean general circulation model on the reproduction of climate changes during the 20th century and on the simulation of possible climate changes during the 21st–22nd centuries according to three IPCC scenarios of variations in the concentrations of greenhouse and other gases, as well as the results of the experiments with the doubled and quadruple concentrations of CO₂, are considered. An increase in the near-surface air temperature during the 20th century and the features of the observed climate changes, such as warming in 1940–1950 and its slowing down in 1960–1970, are adequately reproduced in the model. According to the model, the air-temperature increase during the 22nd century (as compared to the end of the 20th century) varies from 2 K for the most moderate scenario to 5 K for the warmest scenario. This estimate is somewhat lower than the expected warming averaged over the data of all models presented in the third IPCC report. According to model data, in the 22nd century, under all scenarios, at the end of summer, a complete or almost complete sea-ice melting will occur in the Arctic. According to the model, by the year 2200, the sea level will vary by 20 to 45 cm as compared to the level at the end of the 20th century.     

Influence of radiation and circulation factors on climate change in Western Siberia at the end of the 20th century and beginning of the 21st century

An analysis of the air-temperature and atmospheric-pressure fields in Western Siberia is performed based on observations in 1976–2014; a comparison of temperature and pressure variability in two temporal intervals, 1976–2005 and 1985–2014, is carried out. The estimation of contributions from such climate-forming factors as radiation and circulation is performed for the same intervals. It is revealed that an increase in the annual mean ground–air temperature in the investigated region of Western Siberia was still taking place in the period of 1985–2014; however, the warming process was less active than in the 1976–2005 period. Winter months play the largest role in decreasing the temperature growth rate; during these months, the warming process was replaced by a cooling one in the second time interval. It is shown that the circulation factors, that is, the mechanisms described by indices of global circulation, played the dominant role in the period from 1985 to 2014.     

Variability of the Southern Hemisphere Subtropical Jet Stream in the Second Half of the 20th Century and Early 21st Century

Latitudinal position and wind speed of the Southern Hemisphere subtropical jet stream have been investigated on the basis of ERA-Interim, JRA-55, and NCEP–NCAR reanalysis data for 1948–2013. The analysis covers different time intervals in summer and winter seasons, as well as different spatial domains. It has been shown that the variability of the southern jet stream parameters in both winter and summer seasons is predominantly characterized by wind-speed weakening on the jet-stream axis and its poleward shift. The winter seasons of 2000–2013 identified a shift in the jet-stream axis toward the equator in the Atlantic (60°–0° W) and African (0°–60° E) sectors; the wind-speed increase in the Atlantic sector was statistically significant. The wind speed on the jet-stream axis in both winter and summer is closely related to the temperature difference in the upper tropospheric layer of 200–400 hPa between the latitudinal zones of 0°–30° S and 30°–60° S. A significant negative correlation (r = ?0.78) between wind speed and temperature difference has been revealed for the winter season in the upper tropospheric layer between the latitudinal zones of 30°–60° S and 60°–90° S, which can be explained by the Southern Annular Mode variability in this season. No such relationship has been found for the summer season.     

Arctic climate changes and possible conditions of Arctic navigation in the 21st century

Assessments of current and expected climatic changes in the Arctic Basin are obtained, including ice-cover characteristics influencing the duration of the navigation season on the Northern Sea Route (NSR) along Eurasia and the Northwest Passage (NWP) along North America. The ability of modern climate models to simulate the average duration of the navigation season and its changes over recent decades is estimated. The duration of the navigation season for the NSR and NWP in the 21st century is estimated using an ensemble of climate models. The assessments differ significantly for the NSR and NWP. Unlike the NSR, the NWP reveals no large changes in the navigation season in the first 30 years of the 21st century. From the multimodel simulations, the expected duration of the navigation period by the late 21st century will be approximately 3 to 6 months for the NSR and 2 to 4 months for the NWP under the moderate anthropogenic SRES-A1B scenario.     

Age of the western Black Sea basin according to an analysis of the anomalous magnetic field and geological data

Until recently, the ideas about the age of the Black Sea deep-water basin have been based on land geological observations in the coastal areas at the interaction periphery, underwater observations from manned submersibles, and on the data of seismic reflection and refraction studies and drilling. Formerly, the scarcity of the information led to a wide scattering of the age determinations: from the Jurassic to the Eocene. Recently, with the appearance of reliable geological and geophysical data, the range of the age estimates has been considerably reduced during the last few years, although there is no commonly accepted opinion on this issue. Therefore, the first attempt to determine the age of the Western Black Sea basin using an analysis of the anomalous magnetic field is of certain interest. The following results were obtained: the basin probably opened between 71.338 and 71.587 My B.P. (subchron C32n.1r). During the interval 68.737–71.071 My B.P. (subchron C31r), extinction of the spreading axes took place. Thus, the total duration of the Campanian-Maestrichtian phase of the opening was about 3 My (interval from 71.587 to 68.737 My B.P.). This result does not agree with the geological and geophysical data available to date. To solve this problem, collection of new geological data and further studies of the structure of the anomalous magnetic field are required.     

Relation between temperature sensitivity to doubled carbon dioxide and the distribution of clouds in current climate models

The paper considers a relation between equilibrium global warming at doubled carbon dioxide (climate sensitivity) and the distribution of clouds and relative humidity in 18 state-of-the-art climate models. There is a strong correlation among three indices: (1) model climate sensitivity, (2) mean cloud amount change due to global warming, and (3) the difference in cloud amount between the tropics and midlatitudes. In the simulation of the present-day current, models with high sensitivity produce smaller clouds amounts in the tropics and larger cloud amounts over midlatitude oceans than models with low sensitivity. The relative humidity in the tropics is smaller in models with high sensitivity than in models with low sensitivity. There is a similarity between vertical profiles of cloud amount and relative humidity under global warming and vertical profiles of the difference in these quantities averaged over the tropics and midlatitudes. Based on the correlations obtained and observations of cloud amount and relative humidity, an estimate is made of the sensitivity of a real climate system.     

The structure of suspended matter in Lake Baikal according to the data of measurements of light scattering functions

By using light scattering functions measured in Lake Baikal, we compute the characteristics of suspended matter, such as the mass concentration and the number of particles of the mineral and biological fractions, their mean radius, and the parameter of dispersion of mineral particles. The data on the vertical distributions of the characteristics of suspended matter are obtained for various regions of the lake in the summer period. We compare the characteristics of suspended matter in the zones of upwelling and downwelling of waters in Lake Baikal and in the Indian Ocean, which reveals its identical specific composition in these waters.     

Seasonal anomalies of water salinity in the Gelendzhik region of the Black Sea according to shipborne monitoring data

The paper presents results of analyzing the data on the variability of salinity in the upper layer of the coastal zone (including the seasonal thermocline) of the Black Sea during the 2010–2013 warm seasons (April–November). The data for the analysis were obtained from the regularly conducted CTD probing the by R/V Ashamba on a cross section abeam the Golubaya Bay (Gelendzhik). The relationship between salinity anomalies, coastal precipitation, and wind forcing is analyzed. It is shown that the contribution of thermal stratification to the density stratification in the seasonal thermocline is almost always greater than the contribution of salinity stratification, and the ratio of the former to the latter increases from April to November.     

Seasonal and interannual variations of the field of sea-surface temperature in the southwest Atlantic according to the data of satellite and contact measurements

We study the seasonal and interannual variations of the field of sea-surface temperature (SST) in the Southwest Atlantic on the basis of the analysis of three data arrays, namely, the Levitus-Boyer-1994 hydrological array, the WOD-98 actual database, and the data of satellite measurements of SST. We perform the comparative analysis of the amplitude-phase characteristics of the annual course of the SST field and discuss the distinctive features of its seasonal and interannual variations. It is shown that the results obtained by using different data arrays are in good agreement. The values of the coefficient of linear correlation are equal to 0.7–0.9. It is discovered that the maximum seasonal variations of SST are observed in the zone of confluence of the Falkland and Brasil Currents in the vicinities of the South Subtropical and Antarctic Polar fronts. The minimum seasonal variations are recorded in the Antarctic region and in the Weddell Sea. The satellite data demonstrate that the level of interannual variability is high in the zones of climatic fronts. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 62–76, September–October, 2006.     

Properties and changes in empirical orthogonal components of temperature fields in Northern Eurasia in the 20th century

Using data from 55 meteorological stations in the Northern Hemisphere for the 20th century as a whole and separately for 1901–1950 and 1951–2000, the norms and empirical orthogonal components (EOCs) of the fields of the annual mean surface air temperature were calculated. These fields were found to have two components: smooth and nonsmooth. The field of differences between the temperature norms of the first and second halves of the 20th century was found to be projected almost completely on the very first component of fixed sign; i.e., the current climate trend of the Northern Hemisphere is spatially homogeneous. No substantial changes were found in the transition from the first half to the second half of the 20th century, either in the form of components or in the spectrum of eigenvalues, with the only exception being a small growth (in magnitude) in part of the eigenvalues corresponding to the nonsmooth component. This can be explained by the progressing urbanization of northern Eurasia. All coefficients of the temperature-field expansion by natural components are distributed normally, and their temporal correlation functions for smooth components of fields have a form characteristic of processes with long-term memory. The latter manifests itself particularly in the motions of the two main waves of the smooth component and reflects two stages of the current climate warming.     

Numerical Simulation of Variations in Ozone Content,Erythemal Ultraviolet Radiation,and Ultraviolet Resources over Northern Eurasia in the 21st Century

Izvestiya, Atmospheric and Oceanic Physics - The influence of different factors on the total ozone content (TOC) and erythemal UV radiation (Qery) in the atmosphere over northern Eurasia from 1979...     

Estimation of changes in characteristics of the climate and carbon cycle in the 21st century accounting for the uncertainty of terrestrial biota parameter values

ensemble simulations with the A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS) climate model (CM) for the 21st century are analyzed taking into account anthropogenic forcings in accordance with the Special Report on Emission Scenarios (SRES) A2, A1B, and B1, whereas agricultural land areas were assumed to change in accordance with the Land Use Harmonization project scenarios. Different realizations within these ensemble experiments were constructed by varying two governing parameters of the terrestrial carbon cycle. The ensemble simulations were analyzed with the use of Bayesian statistics, which makes it possible to suppress the influence of unrealistic members of these experiments on their results. It is established that, for global values of the main characteristics of the terrestrial carbon cycle, the SRES scenarios used do not differ statistically from each other, so within the framework of the model, the primary productivity of terrestrial vegetation will increase in the 21st century from 74 ± 1 to 102 ± 13 PgC yr⁻¹ and the carbon storage in terrestrial vegetation will increase from 511 ± 8 to 611 ± 8 PgC (here and below, we indicate the mean ± standard deviations). The mutual compensation of changes in the soil carbon stock in different regions will make global changes in the soil carbon storage in the 21st century statistically insignificant. The global CO₂ uptake by terrestrial ecosystems will increase in the first half of the 21st century, whereupon it will decrease. The uncertainty interval of this variable in the middle (end) of the 21st century will be from 1.3 to 3.4 PgC yr⁻¹ (from 0.3 to 3.1 PgC yr⁻¹). In most regions, an increase in the net productivity of terrestrial vegetation (especially outside the tropics), the accumulation of carbon in this vegetation, and changes in the amount of soil carbon stock (with the total carbon accumulation in soils of the tropics and subtropics and the regions of both accumulation and loss of soil carbon at higher latitudes) will be robust within the ensemble in the 21st century, as will the CO₂ uptake from the atmosphere only by terrestrial ecosystems located at extratropical latitudes of Eurasia, first and foremost by the Siberian taiga. However, substantial differences in anthropogenic emissions between the SRES scenarios in the 21st century lead to statistically significant differences between these scenarios in the carbon dioxide uptake by the ocean, the carbon dioxide content in the atmosphere, and changes in the surface air temperature. In particular, according to the SRES A2 (A1B, B1) scenario, in 2071–2100 the carbon flux from the atmosphere to the ocean will be 10.6 ± 0.6 PgC yr⁻¹ (8.3 ± 0.5, 5.6 ± 0.3 PgC yr⁻¹), and the carbon dioxide concentration in the atmosphere will reach 773 ± 28 ppmv (662 ± 24, 534 ± 16 ppmv) by 2100. The annual mean warming in 2071–2100 relatively to 1961–1990 will be 3.19 ± 0.09 K (2.52 ± 0.08, 1.84 ± 0.06 K).     

The structure of the tidal mixing front in the region of Shantar Islands (Sea of Okhotsk) according to data of satellite observations

The location and seasonal variability of the tidal mixing front in the region of Shantar Islands are studied based on an analysis of satellite data. The Shantar tidal mixing front is related to the main features of the oceanographic structure of the northwestern shelf of the Sea of Okhotsk in summer. This front separates the coastal waters mixed by tidal currents and the stratified part of the shelf. The temperature tidal mixing front forms in July after the melting ice cover and disappears in the end of October when the stratification is broken. The mean position of the front changes insignificantly and is determined by the critical value of the Simpson-Hunter parameter (logh/u ₃ = 2.5); the front is located over the isobath of 50 m. The temperature tidal mixing front corresponds to the front in the distribution of chlorophyll a determined from SeaWiFS and MODIS satellite imagery. High (when compared to the stratified part of the shelf) concentrations of chlorophyll a were observed within the zone of intense tidal mixing. Satellite images in the IR range of the spectrum (Landsat-5 TM) demonstrated that the front is dynamically unstable. Mixing effects connected with frontal submesoscale baroclinic eddies have an influence on the structure of the stratified part of the shelf.