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.     

Estimation of the uncertainty of future changes in atmospheric carbon dioxide concentration and its radiative forcing

An ensemble experiment with the IAP RAS CM was performed to estimate future changes in the atmospheric concentration of carbon dioxide, its radiative forcing, and characteristics of the climate-carbon cycle feedback. Different ensemble members were obtained by varying the governing parameters of the terrestrial carbon cycle of the model. For 1860–2100, anthropogenic CO₂ emissions due to fossil-fuel burning and land use were prescribed from observational estimates for the 19th and 20th centuries. For the 21st century, emissions were taken from the SRES A2 scenario. The ensemble of numerical experiments was analyzed via Bayesian statistics, which made the uncertainty range of estimates much narrower. To distinguish between realistic and unrealistic ensemble members, the observational characteristics of the carbon cycle for the 20th century were used as a criterion. For the given emission scenario, the carbon dioxide concentration expected by the end of the 21st century falls into the range 818 ± 46 ppm (an average plus or minus standard deviation). The corresponding global instantaneous radiative forcing at the top of the atmosphere (relative to the preindustrial state) lies in the uncertainty range 6.8 ± 0.4 W m^?2. The uncertainty range of the strength of the climate-carbon cycle feedback by the end of the 21st century reaches 59 ± 98 ppm in terms of the atmospheric carbon dioxide concentration and 0.4 ± 0.7 W m^?2 in terms of the radiative forcing.     

Historical simulation and twenty-first century prediction of oceanic CO2 sink and pH change

A global ocean carbon cycle model based on the ocean general circulation model POP and the improved biogeochemical model OCMIP-2 is employed to simulate carbon cycle processes under the historically observed atmospheric CO 2 concentration and different future scenarios (called Rep- resentative Concentration Pathways, or RCPs). The RCPs in this paper follow the design of Inter- governmental Panel on Climate Change (IPCC) for the Fifth Assessment Report (AR5). The model results show that the ocean absorbs CO 2 from atmosphere and the absorbability will continue in the 21st century under the four RCPs. The net air-sea CO 2 flux increased during the historical time and reached 1.87 Pg/a (calculated by carbon) in 2005; however, it would reach peak and then decrease in the 21st century. The ocean absorbs CO 2 mainly in the mid latitude, and releases CO 2 in the equator area. However, in the Antarctic Circumpolar Current (ACC) area the ocean would change from source to sink under the rising CO 2 concentration, including RCP4.5, RCP6.0, and RCP8.5. In 2100, the anthropogenic carbon would be transported to the 40 S in the Atlantic Ocean by the North Atlantic Deep Water (NADW), and also be transported to the north by the Antarctic Bottom Water (AABW) along the Antarctic continent in the Atlantic and Pacific oceans. The ocean pH value is also simulated by the model. The pH decreased by 0.1 after the industrial revolution, and would continue to decrease in the 21st century. For the highest concentration sce- nario of RCP8.5, the global averaged pH would decrease by 0.43 to reach 7.73 due to the absorption of CO 2 from atmosphere.     

Interaction of the methane cycle and processes in wetland ecosystems in a climate model of intermediate complexity

The climate model of the Institute of Atmospheric Physics of the Russian Academy of Sciences (IAP RAS CM) has been supplemented with a module of soil thermal physics and the methane cycle, which takes into account the response of methane emissions from wetland ecosystems to climate changes. Methane emissions are allowed only from unfrozen top layers of the soil, with an additional constraint in the depth of the simulated layer. All wetland ecosystems are assumed to be water-saturated. The molar amount of the methane oxidized in the atmosphere is added to the simulated atmospheric concentration of CO₂. A control preindustrial experiment and a series of numerical experiments for the 17th–21st centuries were conducted with the model forced by greenhouse gases and tropospheric sulfate aerosols. It is shown that the IAP RAS CM generally reproduces preindustrial and current characteristics of both seasonal thawing/freezing of the soil and the methane cycle. During global warming in the 21st century, the permafrost area is reduced by four million square kilometers. By the end of the 21st century, methane emissions from wetland ecosystems amount to 130–140 Mt CH₄/year for the preindustrial and current period increase to 170–200 MtCH₄/year. In the aggressive anthropogenic forcing scenario A2, the atmospheric methane concentration grows steadily to ≈3900 ppb. In more moderate scenarios A1B and B1, the methane concentration increases until the mid-21st century, reaching ≈2100–2400 ppb, and then decreases. Methane oxidation in air results in a slight additional growth of the atmospheric concentration of carbon dioxide. Allowance for the interaction between processes in wetland ecosystems and the methane cycle in the IAP RAS CM leads to an additional atmospheric methane increase of 10–20% depending on the anthropogenic forcing scenario and the time. The causes of this additional increase are the temperature dependence of integral methane production and the longer duration of a warm period in the soil. However, the resulting enhancement of the instantaneous greenhouse radiative forcing of atmospheric methane and an increase in the mean surface air temperature are small (globally < 0.1 W/m² and 0.05 K, respectively).     

两代耦合海浪的地球系统模式FIO-ESM全球碳循环过程发展

自然资源部第一海洋研究所地球系统模式FIO-ESM是自主研发的、以耦合海浪模式为特色的地球系统模式,包括物理气候模式和全球碳循环模式。该模式从第一代版本FIO-ESM v1.0发展到第二代版本FIO-ESM v2.0,其物理气候模式和全球碳循环模式都取得了改进与提升。FIO-ESM v2.0全球碳循环模式的海洋碳循环模式由v1.0的营养盐驱动模型升级为NPZD(Nutrient-Phytoplankton-Zooplankton-Detritus)型的海洋生态动力学碳循环模型,陆地碳循环模型由v1.0的简单的光能利用率模型升级为考虑碳氮相互作用的碳氮(CN)耦合模型;大气碳循环模型仍为CO₂的传输过程,考虑了化石燃料排放、土地利用排放等人为CO₂排放量。在物理过程参数化方案方面,FIOESM v2.0全球碳循环过程在考虑浪致混合作用对生物地球化学参数的作用的基础上,增加了海表面温度的日变化过程对海-气CO₂通量的影响。已有数值模拟试验结果表明,FIO-ESM v2.0在考虑了更加复杂的碳循环过程后仍具有较好的全球碳循环模...     

Preindustrial, historical, and fertilization simulations using a global ocean carbon model with new parameterizations of iron limitation, calcification, and N2 fixation

The Canadian Model of Ocean Carbon (CMOC) has been developed as part of a global coupled climate carbon model. In a stand-alone integration to preindustrial equilibrium, the model ecosystem and global ocean carbon cycle are in general agreement with estimates based on observations. CMOC reproduces global mean estimates and spatial distributions of various indicators of the strength of the biological pump; the spatial distribution of the air-sea exchange of CO₂ is consistent with present-day estimates. Agreement with the observed distribution of alkalinity is good, consistent with recent estimates of the mean rain ratio that are lower than historic estimates, and with calcification occurring primarily in the lower latitudes. With anthropogenic emissions and climate forcing from a 1850-2000 climate model simulation, anthropogenic CO₂ accumulates at a similar rate and with a similar spatial distribution as estimated from observations. A hypothetical scenario for complete elimination of iron limitation generates maximal rates of uptake of atmospheric CO₂ of less than 1 PgC y⁻¹, or about 11% of 2004 industrial emissions. Even a ‘perfect’ future of sustained fertilization would have a minor impact on atmospheric CO₂ growth. In the long term, the onset of fertilization causes the ocean to take up an additional 77 PgC after several thousand years, compared with about 84 PgC thought to have occurred during the transition into the last glacial maximum due to iron fertilization associated with increased dust deposition.     

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).     

Acidification at the Surface in the East Sea: A Coupled Climate-carbon Cycle Model Study

This modeling study investigates the impacts of increasing atmospheric CO₂ concentration on acidification in the East Sea. A historical simulation for the past three decades (1980 to 2010) was performed using the Hadley Centre Global Environmental Model (version 2), a coupled climate model with atmospheric, terrestrial and ocean cycles. As the atmospheric CO₂ concentration increased, acidification progressed in the surface waters of the marginal sea. The acidification was similar in magnitude to observations and models of acidification in the global ocean. However, in the global ocean, the acidification appears to be due to increased in-situ oceanic CO₂ uptake, whereas local processes had stronger effects in the East Sea. pH was lowered by surface warming and by the influx of water with higher dissolved inorganic carbon (DIC) from the northwestern Pacific. Due to the enhanced advection of DIC, the partial pressure of CO₂ increased faster than in the overlying air; consequently, the in-situ oceanic uptake of CO₂ decreased.     

Simulation and prediction of climate changes in the 19th to 21st centuries with the Institute of Numerical Mathematics, Russian Academy of Sciences, model of the Earth’s climate system

This paper presents results from a simulation of climate changes in the 19th–21st centuries with the Institute of Numerical Mathematics Climate Model Version 4 (INMCM4) in the framework of the Coupled Model Intercomparison Project, phase 5 (CMIP5). Like the previous INMCM3 version, this model has a low sensitivity of 4.0 K to a quadrupling of CO₂ concentration. Global warming in the model by the end of the 21st century is 1.9 K for the RCP4.5 scenario and 3.4 K for RCP8.5. The spatial distribution of temperature and precipitation changes driven by the enhanced greenhouse effect is similar to that derived from the INMCM3 model data. In the INMCM4 model, however, the heat flux to the ocean and sea-level rise caused by thermal expansion are roughly 1.5 times as large as those in the INMCM3 model under the same scenario. A decrease in sea-ice extent and a change in heat fluxes and meridional circulation in the ocean under global warming, as well as some aspects of natural climate variability in the model, are considered.     

Methane cycle in the INM RAS climate model

The atmosphere-ocean general circulation model with the carbon cycle is coupled to a model of methane evolution, in which methane sources in the soil of wetlands and methane evolution in the atmosphere are calculated. A numerical experiment on the simulation of climate and methane-cycle changes in 1860–2100 has been conducted with the model forced by methane emissions prescribed from scenario A1B. The distribution of the sources of methane from soil agrees with the available estimates and amounts to about 240 Mt/year in the 20th century. The methane flux from soil increases to 340 Mt/year by the end of the 21st century. The model adequately reproduces an increase in the atmospheric methane concentration from 800 ppb in 1860 to about 1800 ppb in 2000, but does not produce the observed stabilization of methane concentration in the early 21st century. By 2060, the methane concentration in the model attains 2700 ppb. The increase in atmospheric methane concentration is due mainly to anthropogenic emissions. A similar numerical experiment with fixed sources of methane from soil at the 1860–1900 level suggests that the maximum methane concentration in the model in this case could amount to 2400 ppb. A temperature increase at the end of the 21st century relative to the 19th century is 3.5° for a simulated change in the methane flux from soil and 0.25° less for a fixed methane flux.     

全球海洋碳循环三维数值模拟研究

基于海洋环流模式POP和生物地球化学模型OCMIP-2,建立了全球海洋碳循环模式,并用于对全球海洋碳循环的模拟研究。该模式在大气CO₂为283×10-6条件下,积分3 100 a,达到工业革命前的平衡态。在此基础上,用历史时期观测的大气CO₂浓度进行强迫,模拟了历史时期的海洋碳循环。模拟的无机碳浓度、总碱度与基于观测得到的结果基本一致,模式能够较好地模拟全球碳循环过程。模拟结果表明,在北半球中高纬度和南半球的中纬度,海洋是大气CO₂的主要汇区;在赤道南北纬20°之间和南大洋50°S以南,海洋表现为大气CO₂的源区。在1980s海洋吸收CO₂速率(以C计)为1.38 Pg/a,1990s为1.55 Pg/a。海洋中人为碳在北大西洋含量最大,向下到达海底并向南输运到30°N附近;在南极附近,浓度较小,深度达到3 000 m;在中纬度,人为碳被限制在温跃层以上。     

Modeling the contribution of dissolved organic carbon to carbon sequestration during the last glacial maximum

Dissolved organic carbon (DOC) is a carbon reservoir that is as large as the atmospheric CO₂ pool, and its contribution to the global carbon cycle is gaining attention. As DOC is a dissolved tracer, its distribution can serve to trace the mixing of water masses and the pathways of ocean circulation. Published proxy and model reconstructions have revealed that, during the last glacial maximum (LGM), the pattern of deep ocean circulation differed from that of the modern ocean, whereby additional carbon is assumed to have been sequestered in stratified LGM deep water. The aim of this study is to explore the distribution of DOC and its production/removal rate during the LGM using the Grid ENabled Integrated Earth system model (GENIE). Modeled results reveal that increased salinity of bottom waters in the Southern Ocean is associated with stronger stratification and oxygen depletion. The stratified LGM deep ocean traps more nutrients, resulting in a decrease in the DOC reservoir size that, in turn, causes a negative feedback for carbon sequestration. This finding requires an increase in DOC lifetime to compensate for the negative feedback. The upper limit of DOC lifetime is assumed to be 20,000 years. Modeled results derive an increase (decrease) in DOC reservoir by 100 Pg C leading to an atmospheric CO₂ decrease (increase) of 9.1 ppm and a dissolved inorganic carbon δ¹³C increase (decrease) of 0.06‰. The DOC removal rate is estimated to be 39.5 Tg C year^–1 in the deep sea during the LGM. The contribution of DOC to the LGM carbon cycle elucidates potential carbon sink-increasing strategies.     

Changes in climatic characteristics of Northern Hemisphere extratropical land in the 21st century: Assessments with the IAP RAS climate model

Assessments of future changes in the climate of Northern Hemisphere extratropical land regions have been made with the IAP RAS climate model (CM) of intermediate complexity (which includes a detailed scheme of thermo- and hydrophysical soil processes) under prescribed greenhouse and sulfate anthropogenic forcing from observational data for the 19th and 20th centuries and from the SRES B1, A1B, and A2 scenarios for the 21st century. The annual mean warming of the extratropical land surface has been found to reach 2–5 K (3–10 K) by the middle (end) of the 21st century relative to 1961–1990, depending on the anthropogenic forcing scenario, with larger values in North America than in Europe. Winter warming is greater than summer warming. This is expressed in a decrease of 1–4 K (or more) in the amplitude of the annual harmonic of soil-surface temperature in the middle and high latitudes of Eurasia and North America. The total area extent of perennially frozen ground S _p in the IAP RAS CM changes only slightly until the late 20th century, reaching about 21 million km², and then decreases to 11–12 million km² in 2036–2065 and 4–8 million km² in 2071–2100. In the late 21st century, near-surface permafrost is expected to remain only in Tibet and in central and eastern Siberia. In these regions, depths of seasonal thaw exceed 1 m (2 m) under the SRES B1 (A1B or A2) scenario. The total land area with seasonal thaw or cooling is expected to decrease from the current value of 54–55 million km² to 38–42 in the late 21st century. The area of Northern Hemisphere snow cover in February is also reduced from the current value of 45–49 million km² to 31–37 million km². For the basins of major rivers in the extratropical latitudes of the Northern Hemisphere, runoff is expected to increase in central and eastern Siberia. In European Russia and in southern Europe, runoff is projected to decrease. In western Siberia (the Ob watershed), runoff would increase under the SRES A1B and A2 scenarios until the 2050s–2070s, then it would decrease to values close to present-day ones; under the anthropogenic forcing scenario SRES B1, the increase in runoff will continue up to the late 21st century. Total runoff from Eurasian rivers into the Arctic Ocean in the IAP RAS CM in the 21st century will increase by 8–9% depending on the scenario. Runoff from the North American rivers into the Arctic Ocean has not changed much throughout numerical experiments with the IAP RAS CM.     

The effects of elevated-CO2 on physiological performance of Bryopsis plumosa

An increase in the level of atmospheric carbon dioxide (CO2) and the resultant rise in CO2 in seawater alter the inorganic carbon concentrations of seawater. This change, known as ocean acidification, ...     

Natural air–sea flux of CO2 in simulations of the NASA-GISS climate model: Sensitivity to the physical ocean model formulation

Results from twin control simulations of the preindustrial CO₂ gas exchange (natural flux of CO₂) between the ocean and the atmosphere are presented here using the NASA-GISS climate model, in which the same atmospheric component (modelE2) is coupled to two different ocean models, the Russell ocean model and HYCOM. Both incarnations of the GISS climate model are also coupled to the same ocean biogeochemistry module (NOBM) which estimates prognostic distributions for biotic and abiotic fields that influence the air–sea flux of CO₂. Model intercomparison is carried out at equilibrium conditions and model differences are contrasted with biases from present day climatologies. Although the models agree on the spatial patterns of the air–sea flux of CO₂, they disagree on the strength of the North Atlantic and Southern Ocean sinks mainly because of kinematic (winds) and chemistry (pCO₂) differences rather than thermodynamic (SST) ones. Biology/chemistry dissimilarities in the models stem from the different parameterizations of advective and diffusive processes, such as overturning, mixing and horizontal tracer advection and to a lesser degree from parameterizations of biogeochemical processes such as gravitational settling and sinking. The global meridional overturning circulation illustrates much of the different behavior of the biological pump in the two models, together with differences in mixed layer depth which are responsible for different SST, DIC and nutrient distributions in the two models and consequently different atmospheric feedbacks (in the wind, net heat and freshwater fluxes into the ocean).     

Note on the CO2 air–sea gas exchange at high temperatures

The temperature dependency of ocean–atmosphere gas transfer velocities is commonly estimated in terms of Schmidt numbers, i.e. the ratio of kinematic viscosity to diffusivity. In numerical models least square regressions are used to fit the limited number of experimentally derived Schmidt numbers to a function of temperature. For CO₂ a well established fit can be found in the literature. This fit constitutes an integral part in standardized carbon cycle simulation projects (e.g. C4MIP, OC4MIP, Friedlingstein et al., 2006). However, the fit is valid only in the range where diffusivity measurements exist, i.e., from 0 to about 30 °C. In many climate warming simulations like e.g. the MPI contribution to the fourth Intergovernmental Panel on Climate Change Assessment Report (IPCC AR 4), sea surface temperatures largely exceed the validated range and approach or even reach the range, where the standard fits leave the physically meaningful range. Thus, this paper underlines the demand for new measurements of seawater diffusivities for CO₂ and other trace gases especially for the temperature range >30 °C.In this paper we provide improved fits for the temperature dependence of the Schmidt number. For carbon dioxide our fit is compared to the established fit under identical climate change simulations carried out with the 3D-carbon cycle model HAMOCC. We find that in many tropical and subtropical high temperature regions the established fit leads to unrealistically short adaption times of the surface water pCO₂ to altered atmospheric pCO₂. In regions where the local oceanic pCO₂ is not primarily controlled by the atmospheric boundary pCO₂ but by other processes such as biological activity, the atmosphere ocean pCO₂ gradient is clearly underestimated when using the established fit. The effect on global oceanic carbon uptake in a greenhouse world is rather small and the potential climate feedback introduced by this bias seems to be negligible. However, the bias will clearly gain in significance the more regions warm up to over 30 °C. On a regional scale, especially in coastal regions at low latitudes, the effect is not negligible and a different steady state is approached.     

Causes of a fresher, colder northern North Atlantic in late 20th century in a coupled model

Observational evidence indicates that in the northern North Atlantic, especially in the Labrador Sea, almost the whole column of the ocean water is fresher, and colder in late 20th century than in 1950–1960s. Here we analyze a four-member ensemble of the 20th century simulations from a coupled climate model to examine the possible causes for these observed changes. The model simulations resemble the observed changes in the northern North Atlantic. The simulated results show that a decreased meridional freshwater divergence and an increased meridional heat divergence associated with a weaker thermohaline circulation in the North Atlantic are the primary causes for the freshening and cooling in the northern North Atlantic. The increased precipitation less evaporation tends to enforce the freshening, but the reduced sea ice flux into this region tends to weaken it. On the other hand, the surface warming induced by a higher atmospheric CO₂ concentration tends to heat up the northern North Atlantic, but is overcome by the cooling from increased meridional heat divergence.     

Remote effects of mixed layer development on ocean acidification in the subsurface layers of the North Pacific

Using the outputs of projections under the highest emission scenario of the representative concentration pathways performed by Earth system models (ESMs), we evaluate the ocean acidification rates of subsurface layers of the western North Pacific, where the strongest sink of atmospheric CO₂ is found in the mid-latitudes. The low potential vorticity water mass called the North Pacific Subtropical Mode Water (STMW) shows large dissolved inorganic carbon (DIC) concentration increase, and is advected southwestward, so that, in the sea to the south of Japan, DIC concentration increases and ocean acidification occurs faster than in adjacent regions. In the STMW of the Izu-Ogasawara region, the ocean acidification occurs with a pH decrease of ~0.004 year^?1 , a much higher rate than the previously estimated global average (0.0023 year^?1), so that the pH decreases by 0.3–0.4 during the twenty-first century and the saturation state of calcite (Ω_Ca) decreases from ~4.8 down to ~2.4. We find that the ESMs with a deeper mixed layer in the Kuroshio Extension region show a larger increase in DIC concentration within the Izu-Ogasawara region and within the Ryukyu Islands region. Comparing model results with the mixed layer depth obtained from the Argo dataset, we estimate that DIC concentration at a depth of ~200 m increases by 1.4–1.6 μmol kg^?1 year^?1 in the Izu-Ogasawara region and by 1.1–1.4 μmol kg^?1 year^?1 in the Ryukyu Islands region toward the end of this century.     

Dynamics of a closed low-parameter compartment model of the global carbon cycle

A closed dynamic compartment model of the global carbon cycle and its modifications with a small number of external parameters, which are constructed on the basis of data on the current and preindustrial carbon fluxes and reserves in reservoirs, are studied. The first possible controlling parameter is the amount of anthropogenic CO₂ emission into the atmosphere. Closure in substance allows a decrease in the dimensionality of dynamic models and yields another variable parameter—the system’s total mass, whose change reflects the level of uncertainty in the knowledge of the amount of reserves. The calibration of unsaturated fluxes in each of the models is based on an algorithm developed earlier for local ecosystems, and the measured differences between the fluxes opposite in sign for several times are used to calculate the coefficients of saturated fluxes. The model’s modifications make it possible to estimate the degree to which the oceanic active layer may be involved in rapid exchange with the atmosphere and to introduce the factor of land use as an additional anthropogenic effect. The time trajectories of carbon reserves in reservoirs are calculated until 2100 under variations in anthropogenic emissions in accordance with the IPCC basic scenarios until 2100 for the basic model and its modifications.     

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.