P. F. Demchenko

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).

Simulation of Characteristics of Thermal and Hydrologic Soil Regimes in Equilibrium Numerical Experiments with a Climate Model of Intermediate Complexity

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.

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 Sp 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.

Impact of Global Warming Rate on Permafrost Degradation

The IAP RAS climate model of intermediate complexity is used to analyze the sensitivity of the area of continuous potential permafrost Scont to the rate of global temperature variation Tgl 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, kcont (= Scont, 0t-1dScont/dTgl, where Scont, 0 is the present value of Scont). With a decrease in the linear trend coefficient of Tgl 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, kcont virtually does not vary and remains close to the value obtained from paleoreconstructions of the past warm epochs. Such a dependence of kcont on the rate of global warming is related mainly to the fact that the more rapid increase in Tgl 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 kcont. 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 kcont turns out to be far less (kcont ≈ −0.3 K−1).

Hysteresis of the surface permafrost area dependence on the global temperature

725 It is expected that the general climate warming recorded in the 20th century and in the first decade of the 21st century will continue in the next decades of the 21st century, and possibly for a few more centuries [1, 2]. Such warming should be accompanied by gen eral degradation of the permafrost [1–7]. At present, along with the scenarios of the anthropogenic impact on the climate leading to its further warming, other scenarios are also being considered, which could restore the preindustrial climate state after such warming (see, for example, http://climate.uvic.ca/EMICAR5). In the latter case, the area of permafrost should also return to the preindustrial size. In this work, we use the results of simulations with the global climatic model developed at the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS CM) [2] to find estimates of the response of the permafrost area during climate warming caused by anthropogenic influence on the system and further restoration to the preindustrial climate state. The model contains a detailed block of the processes of thermo and hydro physics of the soil and ground [8]. The horizontal res olution used in this version of the IAP RAS CM is 4.5° by latitude and 6° by longitude.

Air temperature and energy consumption feedbacks within urbanized areas

In the 21st century, the climate of expanding megacities and urbanized areas is increasingly forming and changing under the influence of the growing power consumption of the urban economy. To understand the urban climate dynamic and estimate the energy needs of cities in the 21st century, it is necessary to consider not only global and regional climatic factors, but also the presence of feedback between temperature and energy consumption in urbanized areas. This feedback can be both negative and positive, and their significance depends essentially on the climate and landform of the region, system of electricity and heat supply of a city, and some other factors. This article describes the main factors of formation and development of temperature and energy-consumption feedback within urbanized areas in cold and warm seasons when indoor heating or air conditioning is being used. The role of advection in strengthening and weakening of this feedback is studied. The estimates of the parameter and coefficient of feedback strengthening with the influence of anthropogenic heat fluxes and advection on the urban air temperature are presented.

Influence of Feedbacks in the Climate–Energetics System on the Intensity of an Urban Heat Island

Both horizontal and vertical heat exchanges and feedbacks between air temperature and anthropogenic heat fluxes significantly affect the characteristics of the urban heat island (UHI). The UHI intensity depends, in particular, on the ratio between the scales LA (area of anthropogenic forcing) and Lγ (distance passed by an air particle of the oncoming stably stratified flow before its temperature approaches air temperature within the UHI). Both advection and feedback effects may be estimated based on the equation for the local heat balance of the underlying surface. In this case, heat advection is taken into account by calculating temperatures individually for the atmospheric boundary layer and the surface of the urban canopy layer. The estimates show that the asymptotics of strong advection is more characteristic of a typical city. However, under weak winds, with consideration for the feedback between air temperature and anthropogenic heat flux, some deviations from this asymptotics are probable.

Estimation of uncertainty in surface air temperature climatic trends related to the internal dynamics of the atmosphere

The variability of zonal trends of surface air temperature for the period 1979–2012 is analyzed using ensemble simulations with a general atmospheric circulation model (AGCM) with identical prescribed conditions at the lower boundary of the atmosphere and different initial conditions. It is shown that the dependence of the variability of intra-ensemble zonal temperature trends on the variability of zonal fluctuations of temperature anomalies (associated with the internal variability of atmospheric circulation in the AGCM) is described quite well in terms of the stationary stochastic process model. In such a model, the dependence of the standard deviation of intra-ensemble trends can be approximated by a linear function of the standard deviation of temperature fluctuations, which agrees well with the AGCM results.

Fluctuation-dissipation relationships used for calculating the response of the soil moisture content to atmospheric actions

Methods of stochastic dynamics based on the application of fluctuation theorems (FTs) are used for describing nonstationary responses of natural objects to specified finite, but not necessarily small, changes in external factors in the presence of random disturbances. Nonlinear fluctuation-dissipation relationships (FDRs) are obtained on the basis of one of the FTs. These FDRs are used for calculating the soil moisture content response to specified changes in the mean precipitation in the presence of synoptic disturbances. The model under consideration, in spite of its coarseness, includes an important nonlinear effect of the moisture excess discharge into a reservoir. An approximate analytical theory is constructed. This theory makes it possible to take into account nonlinear effects when response functions are determined.