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anthropogenically

K. Ya. Kondratyev. Key aspects of global climate change. ?

     In context of the results of the World Climate Change Conference which took place in Moscow during the time period September 29 October 3 (WCCC 2003) an analysis has been made of key issues

    of contemporary global climate change. The principal attention has been paid to the discussion of uncertainties of existing observation data and numerical modelling results. As fas as numerical modelling is concerned, a necessity has been emphasized of an analysis of present day models from the viewpoint of their ability to simulate real climate change which results from nonlinear interactions between numerous climatic system‟s components taking also into account potential contributions of cosmic factors such as

    solar activity.

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    K. Ya. KONDRATYEV

    KEY ASPECTS OF GLOBAL CLIMATE CHANGE

    INTRODUCTION

    An unprecedented increase of interest in the problems of climate observed during the last decades (this refers, in particular, to mass media) has stimulated the working out of both scientific and applied developments, which provided a considerable advance in understanding the causes of present climate changes, the laws of paleoclimate, and in substantiation of scenarios of possible changes of climate in future (the matter concerns with scenarios and not with predictions whose possibilities should be assessed as doubtful) [1-146]. Unfortunately, the growing interest in the problems of climate is partly explained by the important role of various speculative exaggerations and apocalyptic predictions (e.g., complete melting of the arctic sea ice in the first half of this century) due to which the problems of climate change formulated as a concept of anthropogenic global warming have become a focus of geopolicy. It is a paradox that Presidents and Prime Ministers of various countries discuss whether the Kyoto Protocol (KP) should be considered as a scientifically justified document. The confusion of the situation is determined, in particular, by lack of sufficiently clear and agreed-upon terminology. Leaving out of account a very complicated situation with the definition of the notion of climate (this subject needs a separate discussion), one should remember, for instance, that in the UN FCCC the notion of climate change was defined as being anthropogenically induced. One of the main unsolved problems consists in the absence of convincing quantitative estimates of the contribution of anthropogenic factors into the formation of global climate (there is no doubt, however, that anthropogenic forcings on climate do exist). Some international documents containing analyses of the present ideas of climate use the prevalent notion of consensus with respect to scientific conclusions drawn in these documents, as if the development of science was determined not by different views and respective discussions but by a general agreement (and even voting) on some concrete problems. Apart from definitions, of importance is the problem of uncertain conceptual estimates concerning various aspects of climate problems. This refers, in particular, to the main conclusion in the summary of the IPCC-2001 report [55]: “… An increasing body of observations gives a

    collective picture of a warming world and most of the observed warming over the last fifty years is likely to have been due to human activities”.

    It is a pity that in the recent (2003) paper in the British newspaper “The Guardian” the former Chairman of IPCC WG-1 Professor J. Houghton compared the threat of anthropogenic climate changes with weapons of mass destruction and accused the USA of their refusal to support the concept of global warming and KP, which, in his opinion, is the basic cause of this threat. No matter how paradoxical it may be, such a statement has been made against a background of an increasing understanding of imperfection of the present global climate models and the absence of their adequate verification, which makes the predictions on the basis of numerical modelling not more than conditional scenarios [61-63, 65-66, 68-69, 72-80, 82, 120, 122]. As for the USA, huge efforts of this country to support climate studies

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    should be backed. These efforts consist in special emphasis on the improvement of the observing systems [28] and on developments in the field of climate problems in general [126,128]. The US expenses on these problems planned for 2004 reach 4.5 billion dollars.

    The statement published on behalf of the intergovernmental group G-8 on 27 July 2003 [117] emphasizes that in the years to come, efforts will be undertaken in three directions: 1) coordination of strategies of global observations; 2) provision of the pure, stable and efficient use of energy; 3) provision of stable agricultural production and biodiversity.

    In the context of climate problems, uncertainty has become a key notion [84]. Of course, there is

    nothing new in that the present views of global climate and the causes of its changes are very uncertain. However, there are principal differences in estimates of the scales of such uncertainties. The basic conclusions of the IPCC-2001 Report are that these uncertainties are not critically important. This has been mentioned, in particular, in the summary of the report in the form of the following conclusion: “There is new and stronger evidence that most of the warming observed over the last fifty years is

    attributable to human activities”.

    The Earth‟s climate system has markedly changed during the time period from the industrial revolution, with some changes having been of anthropogenic origin. The climate change consequences determine a serious challenge to people responsible for the ecological policy, which determines an urgency of objective information on climate change, its impact and possible response to climate change. With this aim in view, the World Meteorological Organization (WMO) and the UN Environmental Programme organized in 1988 the Intergovernmental Panel on Climate Change. The IPCC incorporates three working groups (WG) whose spheres of responsibility include: 1) scientific aspects of climate and its change (WG-I), 2) effects on and adaptation to climate (WG-II), 3) analysis of possibilities to limit (restrain) climate changes (WG-III).

    During the last years the IPCC prepared three detailed reports (1990, 1996, 2001) as well as some special reports and technical papers. Griggs and Noguer [41] made a bried review of the first volume of the Third IPCC Report (TAR) prepared by WG-I for the period June 1998 January 2001 with the

    perticipation of 122 leading authors and 515 experts, each with their materials. Four hundred and twenty experts reviewed the first volume and 23 experts edited it. Besides, several hundred reviewers and representatives of many governments made additional remarks. With the participation of delegates from 99 countries and 50 scientists recommended by the leading authors, the final discussion of TAR was held in Shanghai on 17-20 January 2001. “Summary for decision-makers” was approved after a detailed

    discussion by 59 specialists.

    Analysis of the observation data contained in TAR has led to the conclusion about the presence of global climate change. In this connection, the Report [55] gives a detailed review of the data of observations of the spatial-temporal variability of concentrations of various GHGs and aerosol in the atmosphere. An adequacy of numerical models has been discussed from the viewpoint of consideration of the climate-forming factors and usefulness of models to predict climate change in the future. The main conclusion about anthropogenic impacts on climate is that “there is new and stronger evidence that most

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    of the warming observed during the last 50 years has been determined by human activity”. According to

    stall prognostic estimates considered in TAR, during the 21 century both SAT increase and sea level rise

    should take place.

    When characterizing the IPCC data on the empirical diagnostics of climate, Folland et al. [32] drew attention to the uncertainty of definitions of some basic notions. According to the IPCC therminology, climate changes are statistically substantial variations of an average state or its variability, whose stability is preserved for long time periods (decades and longer). Climate changes can be of natural origin (connected both with internal processes and exteernal impacts) and (or) they can be determined by anthropogenic factors (changes in the atmospheric composition or land use). This definition differs from that suggested in the Framework Climate Change Convention (FCCC) where climate changes are only of anthropogenic origin in contrast to natural climate changes. In accordance with the IPCC therminology, climatic variability means variations of the average state and other statistical characteristics (dispersion, repeatability of extreme events, etc.) of climate on every temporal and spatial scale, beyond individual weather phenomena. The climate variability can be both of natural (due to internal processes and external forcings) and anthropogenic origin. These are internal variability and external variability. As Folland et al. [32] noted, seven key questions are most important for diagnostics of the observed changes and variability of climate: 1) how much significat is climate warming? 2) is the present warming significant? 3) how rapidly had the climate changed in the distant past? 4) have precipitation and atmospheric water content changed? 5) do changes of general circulation of the atmosphere and ocean take place? 6) have the climate variability and climate extremes changed? 7) are the observed trends internally coordinated?

    The observation data reliability plays the fyndamental role for the adequate empirical diagnostics of climate. However, information about numerous meteorological parameters, which is very important for documentation, detection and attribution of climate changes, is inadequate for reliable conclusions. This especially concerns the global trends of parameters (e.g., precipitation) which are characterized by a great regional variability.

    Folland et al. [32] answered the questions above. A comparison of the secular change of average global avrtage annual sea surface temperature (SST), land surface air temperature (LSAT) and nocturnal air temperature over the ocean (NMAT) for the period 1861-2000 revealed on the whole some similarity though the warming in the 1980s from LSAT data turned out to be stronger, and the NMAT data showed

    tha moderate cooling in the end of the 19 century, not demonstrated by SST data. The global trend of

    temperature can be cautiously interpreted as an equivalently linear warming over 140 years constituting

    ooo0.61C at a 95% confidence level with an uncertainty ?0.16C. Later on, in 1901 a warming by 0.57C

    otook place with an uncertainty ?0.17C. These estimates suggested the conclusion that beginning from the

    thoend of the 19 century, an average global warming by 0.6C took place with the interval of estimates

    ocorresponding to a 95% confidence level equal to 0.4-0.8C.

    thThe spatial structure of the temperature field in the 20 century was characterized by a

    comparatively uniform warming in the tropics, but a considerable variability in the extratropical latitudes. The warming between 1910 and 1945 was initially concentrated in the Northern Atlantic and the adjacent

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    regions. The Northern Htmisphere was characterized by a cooling between 1946 and 1975, while in the Southern Hemisphere some warming was observed in this period. The temperature rise during several last decades (1976-2000) turned out, on the whole, to be globally synchronous and was clearly manifested on the Northern Hemisphere continents in winter and in spring. In some Southern Hemisphere regions and in the Antarctic there was a small all-year-round cooling. A temperature decrease in the Northern Atlantic between 1960 and 1985 was later followed by an opposite trend. On the whole, the climate warming over the period of measurements was more uniform in the Southern Hemisphere than in the Northern Hemisphere. In many continental regions in the period 1950-1993 the temperature increased more rapidly at night than in the day time (this does not refer, however, to the coastal regions). The rate of temperature

    oincrease varied from 0.1 to 0.2C/10 years.

    According to the data of aerological observations, the air temperature in the lower and middle

    otroposphere was increasing after 1958 at a rate of 0.1C/10 years, but in the upper troposphere (after 1960)

    it pracically remained constant. A combined analysis of the aerological and satellite information has shown that in the period 1979-2000 the temperature trend in the lower troposphere was weak, whereas

    onear the land surface it turned out to be statistically significant and reached 0.16?0.06C/10 years. The

    statistically substantial trend of the difference between the Earth‟s surface and the lower troposphere

    oconstituted 0.13?0.06C/10 years, which differs from the data for the period 1958-1978, when the average

    oglobal temperature in the lower troposphere increased more rapidly (by 0.03C/10 years) than near the

    surface. Considerable differences between the temperature trends in the lower troposphere and near the surface are most likely real. So far, these differences cannot be convincingly explained. The climate

    thwarming in the Northern Hemisphere observed in the 20 century was the most substantial over the last

    1000 years [94]. Due to [32], the observation data do not permit to confirm the global scales of the warming in the Minor Ice Age and Middle Age periods. However, both these conclusions remain contradictory [97].

    Special attention has been paid to the discussion in the IPCC-2001 Report of possibility to predict future climate changes. The chaotic character of the atmospheric dynamics limits the long-term weather forecasts by one-two weeks and hinders the prefiction of a detailed climate change (e.g., it is impossible to predict precipitation in Great Britain for the winter of 2050). However, it is possible to consider climate projections, that is, to develop scenarios of probable climate changes due to continuing growth of GHGs concentrations in the atmosphere. Such scenarios may be useful for decision-makers in the field of ecological policy. The basic means to substantiate such scenarios are numerical climate models that simulate interactive processes in the climatic system “atmosphere-ocean-land surface-cryosphere-

    biosphere”. As Collins and Senior [26] noted, there are many such models, and in this respect a serious difficulty is connected with an almost unsoluble problen of choosing the best model. There remain only a possibility to compare the climate scenarios obtained using various models.

    According to the IPCC recommendations, four levels of projections reliability are considered: 1) from reliable to very probable (in this case there is an agreement between the results for most of the models); 2) very probable (an agreement of new projections obtained with the latest models; 3) probable

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    (new projections with an agreement for a small number of models); 4) restrictedly probable (model results are not certain but changes are physically possible). A principal difficulty in substantiation of projections consists in impossibility to unanimously predict the evolution of GHGs in the future, which determines a necessity to take into account a totality of various scenarios. The huge thermal inertia of the World Ocean dictates a possibility of delayed climatic impact of the GHGs concentrations which had already increased.

    Calculations of average annual average global SAT using the energy-balance climate model with various scenarios of the temporal variations of CO concentrations have led to SAT intervals in 2020, 2

    o2050, and 2100 to be 0.3-0.9, 0.7-2.6, and 1.4-5.8C, respectively. Due to the ocean thermal inertia, a

    odelayed warming should manifest itself within 0.1-0.2C/10 years (such a delay can take place during

    several decades).

    The following conclusions can be attributed to the category of projections of the highest reliability [26]: 1) the surface air warming should be accompanied by a tropospheric warming and stratospheric cooling (the latter is due to a decrease of the upward longwave radiation flux from the troposphere); 2) a faster warming on land compared to oceanic regions (as a result of the great thermal inertia of the ocean); a faster warming in the high-mountain regions (due to albedo feedbacks); 3) the aerosol-induced atmospheric cooling holds a SAT increase (new estimates suggest the conclusion about a weaker manifestation of the aerosol impact); 4) the presence of the warming minima in the North Atlantic and in the circumpolar regions of the oceans in the Southern Hemisphere due to mixing in the oceanic thickness; 5) a decrease of the snow and sea ice cover extent in the Northern Hemisphere; 6) an increase of the average global content of water vapour in the atmosphere, enhancement of precipitation and evaporation, as well as intensification of the global water cycle; 7) intensification (on the average) of precipitation in the tropical and high latitudes, but its attenuation in the sub-tropical latitudes; 8) an increase of precipitation intensity (more substantial than expected as a result of precipitation enhancement, on the average); 9) a summertime decrease of soil moisture in the middle regions of the continents due to intensified evaporation; 10) an intensification of the El Niño regime in the tropical Pacific with a stronger warming in the eastern regions than in the western ones, which is accompanied by an eastward shift of the precipitation zones; 11) an intensification of the interannual variability of the summer monsoon in the Northern Hemisphere; 12) a more frequent appearance of high temperature extrema but infrequent occurrence of temperature minima (with an increasing amplitude of the diurnal temperature course in