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A. V. Eliseev I. I. Mokhov M. M. Arzhanov P. F. Demchenko S. N. Denisov 《Izvestiya Atmospheric and Oceanic Physics》2008,44(2):139-152
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). 相似文献
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The thermobaric conditions of the formation, stability, and dissociation of continental gas hydrates were determined by simulation of the thermal state of the permafrost. The calculations covered the period over the last 130 000 years, taking into account the various paleo-settings, including continental glaciation, marine transgression, and high geothermal fluxes. According to the numerical calculations, relict gas hydrates may currently exist in the metastable state in the permafrost at depths of less than 100–150 m.
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M. M. Arzhanov P. F. Demchenko A. V. Eliseev I. I. Mokhov 《Izvestiya Atmospheric and Oceanic Physics》2008,44(5):548-566
The IAP RAS CM (Institute of Atmospheric Physics, Russian Academy of Sciences, climate model) has been extended to include a comprehensive scheme of thermal and hydrologic soil processes. In equilibrium numerical experiments with specified preindustrial and current concentrations of atmospheric carbon dioxide, the coupled model successfully reproduces thermal characteristics of soil, including the temperature of its surface, and seasonal thawing and freezing characteristics. On the whole, the model also reproduces soil hydrology, including the winter snow water equivalent and river runoff from large watersheds. Evapotranspiration from the soil surface and soil moisture are simulated somewhat worse. The equilibrium response of the model to a doubling of atmospheric carbon dioxide shows a considerable warming of the soil surface, a reduction in the extent of permanently frozen soils, and the general growth of evaporation from continents. River runoff increases at high latitudes and decreases in the subtropics. The results are in qualitative agreement with observational data for the 20th century and with climate model simulations for the 21st century. 相似文献
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Modelling of the thermal regime of permafrost soils has made it possible to estimate the stability of methane hydrates in the continental permafrost in the Northern Eurasian and North American regions with the risk of gas emissions into the atmosphere as a result of possible dissociation of gas hydrates in the Holocene Optimum and under contemporary climatic conditions [1, 2]. 相似文献
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P. F. Demchenko A. V. Eliseev M. M. Arzhanov I. I. Mokhov 《Izvestiya Atmospheric and Oceanic Physics》2006,42(1):32-39
The IAP RAS climate model of intermediate complexity is used to analyze the sensitivity of the area of continuous potential permafrost S cont to the rate of global temperature variation T gl in experiments with greenhouse-gas increases in the atmosphere. The influence of the internal variability of the model on the results is reduced by conducting ensemble runs with different initial conditions and analysis of the ensemble means. Idealized experiments with a linear or exponential dependence of the concentration of carbon dioxide in the atmosphere have revealed an increase in the magnitude of the temperature-sensitivity parameter of the area of continuous potential permafrost, k cont (= S cont, 0 t-1 dS cont/dT gl, where S cont, 0 is the present value of S cont). With a decrease in the linear trend coefficient of T gl from about 3 to about 2 K/100 yr, this parameter varies from approximately ?0.2 to ?0.4 K?1. With an even slower change in global temperature, k cont virtually does not vary and remains close to the value obtained from paleoreconstructions of the past warm epochs. Such a dependence of k cont on the rate of global warming is related mainly to the fact that the more rapid increase in T gl leads to a slower response over high-latitude land. The contribution from changes in the annual temperature cycle, though comparable in the order of magnitude, is about one-third as large as the contribution from the variation of the latitudinal structure of the response of annual mean temperature. The total reduction in the annual cycle of temperature during warming partly compensates for the effect of the annual mean temperature rise, thus decreasing the magnitude of k cont. In numerical experiments with greenhouse gas changes in accordance with SRES scenarios A2 and B2 and scenario IS92a, there is also a monotonic increase in the magnitude of the normalized parameter of temperature sensitivity of the area of continuous permafrost with a decrease in the growth rate of global temperature. For scenarios A2-CO2, IS92a-GHG, IS92a-CO2, B2-GHG, and B2-CO2, its value is almost indistinguishable from the steady-state asymptotic value of ?0.4 K?1. For A2-GHG, the magnitude of k cont turns out to be far less (k cont ≈ ?0.3 K?1). 相似文献