A. A. Karpenko

Assessments of the relationship of changes of the global surface air temperature with different natural and anthropogenic factors based on observations

We obtained estimates of the relationship of changes in the global surface air temperature (GSAT) with different natural and anthropogenic factors based on empirical data beginning from the middle of the 19th century using the Granger causality test estima� tion and application of cross wavelet analysis. Along with the solar and volcanic activity and changes of the carbon dioxide concentration in the atmosphere, we estimated the role of quasicyclic processes in the Earths climatic system. We analyzed the climatic vari� ations detected by the index of the Atlantic multidec� adal oscillation (AMO) with a characteristic period of approximately 60-70 years and the variations in the angular velocity of the Earth. We made a conclusion on the basis of the empirical regression models based on data beginning from the middle of the 19th century that the changes of the CO2 concentration in the atmosphere have a determining influence on the longterm (secular) GSAT trends. The natural climatic cycles with periods of a few decades influence significantly only on the relatively fast GSAT variations. The influence of natural factors related to solar and volcanic activity on the longterm trends appeared to be much less significant. One of the modern key problems is estimating the role of natural and anthropogenic factors of global cli� mate changes. The natural climatic variability not related to external forcing is characterized by a wide spectrum of temporal and spatial scales and the effects of an anthropogenic character can hardly be distin� guished against the background of the natural variabil� ity. The problem of distinguishing the anthropogenic influence is strongly complicated by the effects of non� linearity and stochasticity in the climatic system under

Influence of direct sulfate-aerosol radiative forcing on the results of numerical experiments with a climate model of intermediate complexity

The climate model of intermediate complexity developed at the Institute of Atmospheric Physics of the Russian Academy of Sciences (IAP RAS CM) is extended by a block for the direct anthropogenic sulfate-aerosol (SA) radiative forcing. Numerical experiments have been performed with prescribed scenarios of the greenhouse and anthropogenic sulfate radiative forcings from observational estimates for the 19th and 20th centuries and from SRES scenarios A1B, A2, and B1 for the 21st century. The globally averaged direct anthropogenic SA radiative forcing FASA by the end of the 20th century relative to the preindustrial state is −0.34 W/m2, lying within the uncertainty range of the corresponding present-day estimates. The absolute value of FASA is the largest in Europe, North America, and southeastern Asia. A general increase in direct radiative forcing in the numerical experiments that have been performed continues until the mid-21st century. With both the greenhouse and the sulfate loadings included, the global climate warming in the model is 1.5–2.8 K by the end of the 21st century relative to the late 20th century, depending on the scenario, and 2.1–3.4 K relative to the preindustrial period. The sulfate aerosol reduces global warming by 0.1–0.4 K in different periods depending on the scenario. The largest slowdown (>1.5 K) occurs over land at middle and high latitudes in the Northern Hemisphere in the mid-21st century for scenario A2. The IAP RAS CM response to the greenhouse and the aerosol forcing is not additive.

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.

Climate Changes in Siberia

This chapter provides observational evidence of climatic variations in Siberia for three time scales: during the past 10,000 years, during the past millennium prior to instrumental observations, and for the past 130 years during the period of large-scale meteorological observations. The observational evidence is appended with the global climate model projections for the twenty-first century based on the most probable scenarios of the future dynamics of the major anthropogenic and natural factors responsible for contemporary climatic changes. Historically, climate of Siberia varied broadly. It was both warmer and colder than the present. However, during the past century, it became much warmer; the cold season precipitation north of 55°N increased, but no rainfall increase over most of Siberia has occurred. This led to drier summer conditions and to increased possibility of droughts and fire weather. Projections of the future climate indicate the further temperature increases, more in the cold season and less in the warm season, significant changes in the hydrological cycle in Central and southern Siberia (summer dryness), ecosystems’ shifts, and changes in the permafrost distribution and stability. Observed and projected frequencies of various extreme events have increased recently and are projected to further increase. While in the north of Siberia, contemporary models predict warmer winters at the end of the twenty-first century and paleoreconstructions hint to warmer summers compared to the present warming observed during the period of instrumental observations. These three groups of estimates are broadly consistent with each other.

Sensitivity of the IFA RAN Global Climatic Model with an interactive carbon cycle to anthropogenic influence

The estimates of the sensitivity of the IFA RAN Global Climatic Model [1] with an interactive carbon cycle to anthropogenic influence were obtained. In the numerical calculations using the IFA RAN model, anthropogenic emission of carbon dioxide into the atmosphere was specified on the basis of data from observations in 1860–2000, and according to the SRES-A2 and SRES-B2 scenarios for 2000–2100 [2, 3]. Inclusion of the interaction with the carbon cycle into the global climatic model enhanced its temperature sensitivity to the increase of carbon dioxide emission into the atmosphere in the 21st century. This is a consequence of less intense sink of CO 2 from the atmosphere into land ecosystems under the condition of anthropogenic warming of the climate.

Global Warming Mitigation by Means of Controlled Aerosol Emissions into the Stratosphere: Global and Regional Peculiarities of Temperature Response as Estimated in IAP RAS CM Simulations

The problem of climate warming mitigation by means of controlled sulphur emissions into the stratosphere has become of growing interest in recent years. Using the IAP RAS global climate model with uniform horizontal distribution of stratospheric aerosols, it has been shown that a complete compensation of global warming, realizable under the SRES A1B scenario of the anthropogenic impact on climate, requires stratospheric sulfate emissions of 5–16 TgS/yr (depending on the chosen values of stratospheric aerosol parameters) in the middle and of 10–30 TgS/yr at the end of the 21st century. Such emissions will result in the essential additional aerosol pollution of the troposphere due to the sedimentation of stratospheric aerosol particles there. Significant-in-magnitude regional anomalies of the surface air temperature of different signs occur in global warming compensation in different regions. Warming compensation in the most sensitive to climate forcing Earth regions (in particular, Siberia), additionally increases the required emissions of stratospheric aerosols by about 10%. In addition, in the case of ceasing such controlled climate forcing, its temperature effect vanishes in one to two decades with a sharp acceleration of global and regional near-surface warming in this period. Thus, the rate of regional temperature changes will attain 3–4 K/decade if the compensating action ceases in 2075.

Model Estimations of Possible Climatic Changes in 21st Century at Different Scenarios of Solar and Volcanic Activities and Anthropogenic Impact

We have made estimations of climatic changes in the 21st century at different scenarios of changes in the solar and volcanic activities using ensemble calculations with the help of a three-dimensional climatic model taking the carbon cycle into account. This model was developed in the Oboukhov Institute of Atmospheric Physics, Russian Academy of Sciences. An ensemble of scenarios is used for possible changes of the solar radiation flux in the 21st century, based on different methods of extrapolation of the data for the period 1610–2000. Along with this, different scenarios of volcanic activity in the 21st century are used. The results of thus made calculations are indicative of a rather small role played by the solar activity variations in changes of the global mean annual near-surface temperature in the 21st century as compared to the expected anthropogenic impact. Model changes of the global near-surface temperature in the 21st century (possible variations of the solar radiation and volcanic activity included) are characterized by a general increase determined in the main by anthropogenic SRES scenarios.

Interrelation between Variations in the Global Surface Air Temperature and Solar Activity Based on Observations and Reconstructions

The key problem of climatic research is related tothe diagnostics of the relative role of natural andanthropogenic factors in modern climate changes. Inthis case, the necessary tools are 3D numerical modelsof the climate with interacting atmosphere, ocean,active layer of soil, cryosphere, and biosphere. Solarand volcanic activities are among the significant factorsinfluencing climatic variations. In this work, we ana-lyzed the interrelation between variations in the globalsurface temperature and solar radiation based on theannual observation and reconstruction data for the 17–20th centuries and the results of numerical experimentswith our 3D global climatic model IAP RAS CM.We used two versions of reconstructions of interan-nual variations in solar radiation [1] (1610–1994) and[2] (1680–1992) without taking other factors intoaccount. Numerical experiments using the IAP RASCM were performed [3–5] for both versions of thereconstructions. It is worth noting that the results of thecomparative analysis of the reconstruction data [1] and[2] reveal notable quantitative differences. For exam-ple, a decrease in the solar constant (with respect to thepresent value) during the Maunder Minimum was equalto 0.24% according to the data in [1] and 0.3% accord-ing to the data in [2]. In the analysis, we also applied thedata of annual global surface air temperature (AGSAT)based on instrumental measurements [6] (1861–2004).The results of numerical experiments using the IAPRAS CM are presented in Fig. 1. According to themodel calculations, the increase in AGSAT by the endof the 20th century (with respect to the Maunder Mini-mum) and in the beginning of the 18th century is ~0.45 Kand ~0.60 K based on reconstructions [1] and [2],respectively. The corresponding values of warming(with respect to the Dalton Minimum) at the boundarybetween the 18th and 19th centuries are equal to 0.55and 0.40 K. These estimates are close to those obtainedusing the global climatic models ECHAM3/LSG [7]and GISS [8]. In the second half of the 20th century, theincrease in the AGSAT in the IAP RAS CM is equal to0.10–0.15 K or 1/6–1/4 of the corresponding warmingbased on observations for that period [6, 9]. The resultsof the calculations indicate that variations in solar activ-ity have made a notable (although not crucial) contribu-tion to global warming in recent decades.We used different methods, in particular, methods ofwavelet and cross wavelet analysis [10, 11] (see also[12]), to carry out a more detailed study of the peculiar-ities of variations in the solar activity and temperatureregime of the earth’s climatic system and their corre-lated variations. Figure 2 shows results of the waveletanalysis of solar radiation based on the data in [1, 2]and the analysis of AGSAT based on the instrumentalmeasurement data [6] (1681–2004). Significant cycleswith periods approximately equal to 11, 50, and 100 yrare characteristic of the time series of solar activityreconstruction. A longer cycle with a period of approx-imately 170–190 yr can also be distinguished.Location and depth of spectral minima are alsoimportant characteristics along with the spectral max-ima. In particular, according to the data in [1], a clear min-imum in solar activity was found at periods of ~140 yr. Inaddition, a weaker minimum at periods two timessmaller (~70 yr) can be distinguished. Close minima(~130–140 and ~65–70 yr) were found in the spectra ofsolar activity from the data in [2]. They are clearer thanthose obtained from the data in [1].Spectral characteristics of AGSAT differ significantlyfrom those obtained for solar activity. The ~50-yr-longcycle is similarly to the spectrum of solar activity. How-ever, it is less significant (with respect to the tempera-