Astronomical theory of climatic change: Status and problem

Quaternary paleotemperatures and sea level records, from both deep sea cores and dated shorelines, provide the basis for testing the Milankovitch hypothesis of climatic change. The longest and most detailed records include (1) oxygen isotope analyses of Caribbean and Atlantic deep sea cores, (2) paleoecological analyses of the same cores, and (3) radiometrically dated raised coral reefs from New Guinea and elsewhere, representing times of relatively high Quaternary sea levels. Time-domain and frequency-domain analysis of these records, shows with a high degree of certainty that Quaternary climatic changes are strongly influenced by the obliquity perturbations and precession of the Earth's orbit. The same analyses also suggest that the time scale adopted by Emiliani for deep sea cores may be more nearly correct than alternative time scales of other workers.The question of whether insolation changes arising from orbital perturbations can generate ice ages, has been disputed by climatologists. It is shown here that orbital perturbations cannot affect climate indirectly through agencies originating within the Earth, such as vulcanism, and that the primary climatic control is therefore through variation of insolation distribution, as Milankovitch suggested. The conclusion is that climatologic theory must accommodate these facts.     

陨击天文事件与新生代全球气候变化

全球范围内已确认的新生代陨击天文事件有8次,根据陨击直接证据或板块构造演化等推测的陨击事件至少还有3次,这些陨击天文事件都对应了新生代不同程度的气候变化。新生代全球气候变化的触发因素主要包括陨击天文事件、地球轨道参数变化、CO₂浓度降低和全球碳循环变化、海洋及大气系统大量甲烷水合物释放、洋流变化及全球规模的构造运动(如构造隆升、超地幔柱、大规模火山活动)等,陨击天文事件是全球气候变化最主要的触发因素。     

Unravelling the evidence of climatic change

Book reviewed in this article:
Mörner, N-A. & Karlén, W. (eds.) 1984: Climatic Changes on a Yearly to Millennial Basis .     

Nondeterministic theories of climatic change

A basic assumption in some climatic theories is that, given the physical properties of the atmosphere and the underlying ocean and land, specified environmental parameters (amount of solar heating, etc.) would determine a unique climate and that climatic changes therefore result from changes in the environment. The possibility that no such unique climate exists and that nondeterministic factors are wholly or partly responsible for long-period fluctuations of the atmosphere-ocean-earth system, is considered. A simple difference equation is used to illustrate the phenomena of transitivity, intransitivity, and almost-intransitivity. Numerical models of moderate size suggest that almost-intransitivity might lead to persistence of atmospheric anomalies for a whole season. The effect of this persistence could be to allow substantial anomalies to build up in the underlying ocean or land, perhaps as abnormal temperatures or excessive snow or ice. These anomalies could subsequently influence the atmosphere, leading to long-period fluctuations. The implications of this possibility for the numerical modeling of climate, and for the interpretation of the output of numerical models, are discussed.     

Physical evidence of Quaternary climatic change

Changes of climate have characterized parts, and at times apparently all, of Earth's surface. Changes that have occurred during the Quaternary period have special significance because, being comparatively recent, they are revealed by physical geologic features that are still at or near the surface, as yet little damaged by erosion. Although some of these features can be interpreted in terms that are broadly quantitative, most are still only qualitative in that they are limited to specifying climatic parameters that are positive or negative relative to those prevailing today in the same area. The common parameters indicated by the physical evidence include temperature (mean annual or summer) and precipitation (mean annual or seasonal). More rarely directions and minimum speeds of effective winds can be specified. A useful basis for reconstructions of former climates is a checklist of the relict geologic features from which climatic inferences can be drawn. Such a list is given here.     

Evaluation of climatic change through harmonic analysis

In the present work, a precipitation and temperature series from Barcelona (Spain) are analysed in order to detect the possible existence of climatic changes or cycles. The analysis is carried out both from the temporal and spectral standpoints. The techniques used range from the classical periodogram and Blackman-Tukey method through to the Maximum Entropy method. The results do not show the existence of climatic cycles, though they do show a clear tendency toward increased precipitation and decreased temperature, since the last years of series.     

Reversal of erosion cycle and climatic change

Successive surveys of the cross section of ephemeral channels in New Mexico over a period of 15 years 1960–1975, show that arroyos that were actively eroding early in the century have reversed the trend and are alluviating. This appears to be associated with the worldwide cooling trend that began about 1940. If the inference proves to be correct, it is significant hydrologically, for it provides some specific knowledge of the climatic conditions associated with the alternate periods of valley erosion and valley alluviation that created the widespread terraces of the semiarid West.     

Beijing international symposium on climatic change

Reports

Beijing international symposium on climatic change     

Regionality of climatic change in East Asia

Regional differences in climatic change are of importance in order to establish the counter-measures for the damage by anomalous climate to agricultural production. It is not unusual for some regions to suffer floods while droughts occur in nearby regions at the same time. This paper deals mainly with the regionality of climatic change in E Asia during recent years, using the year-climate method expressed by the Köppen's system of climatic classification. Occurrence frequencies of BW, BS, Cf, Cw, Dwa, Dwb, and Dwc-type showed striking regionalities, which were obtained from the data at the 134 observatories over E Asia during the period from 1951 to 1970. The distribution of climatic types in each year shows various tendencies: Wet and cold as in 1954 and 1957 shows a pattern in which the boundary between C-type and D-type runs south and the Cfa-zone is broad, extending from middle E China to SW Japan. In contrast, in dry and warm years like 1965, the Dwa regions disappear in the N of E China and the BS region is located just north of the Cwa region, which is distributed broadly from China to Japan. Occurrence frequencies of year climate during the last 100 years were calculated for the 4 stations: Hong Kong, Manila, Shanghai and Tokyo. The results were compared with the distribution types of winter temperature and summer precipitation in China. It seems that the precipitation conditions in summer were reversed between the Philippines and China. Summarizing the results obtained, a schema of the regionality of climatic fluctuation in E and SE Asia was given in relation to the upper air streams. The position of the subtropical jet stream in winter shows a close relationship to the N limit of the Aw and Am year climate regions and in summer with the S limit of Dw region in NE China and North Korea. The Cw and Cf year climate regions in E Asia are located roughly in the regions bounded by the axes of subtropical jet streams in winter and in summer. The Dw year climate region in the E of the Tibetan Plateau reflects the altitudinal effect of the Cw climate of SE China. The N of E China has the variable BS year climate, which may related to the summer and winter jet stream conditions. Finally, the interannual change of the agricultural production index was dealt with in relation to the occurrence frequency of year climate types over E Asia during the years 1967–1970. As far as this period is concerned, the drier conditions are more effective than the wetter conditions in reducing agricultural production.     

Permafrost features as evidence of climatic change

Permafrost features indicate certain upper limits for annual air and ground temperatures, with the air temperatures being usually the lower because of insulating snow and vegetation. The following features generally imply mean annual air temperatures no higher than those indicated and commonly lower: permafrost itself, large sorted forms of patterned ground, palsas, and rock glaciers, 0°C; ice-wedge polygons and well-developed soil-wedge polygons, ?5°C; open-system pingos, ?2°C; closed system pingos, ?6°C; the implication of cryoplanation terraces remains to be established, with estimates ranging from near 0° to ?12°C.Use of fossil permafrost features as temperature indicators is complicated by problems of correct identification and dating, soil type, and local and regional environmental variables such as precipitation and vegetation. Nevertheless the fact that certain maximum paleotemperatures can be reasonably established in places warrants expanded research in former periglacial areas to evaluate temperature increases to the present. The majority of determinations in Europe, where most of the work has been done to date, indicate minimum air temperature increases of 13°–18° since the maximum of the last glaciation.     

Asynchronous Holocene climatic change across China

A review of Holocene climatic variations in different parts of China shows that they were asynchronous. Proxy data from ice cores, pollen, loess, lacustrine sediments, and changes of sea and lake levels demonstrate that many warm and cold oscillations have occurred in China during the Holocene, including a most important climatic event known as the “Holocene optimum,” a milder and wetter period, and that the duration and amplitude of the optimum period, as well as its start and end times, differed in different parts of China. Uplift of the Tibetan plateau over the past millions of years led to the development of the monsoon climate and to complex atmospheric circulation over continental China during the Holocene. As a result, the Holocene optimum began and terminated earlier in high-altitude regions of western China than at lower elevations in eastern China, and the amplitude of the variations was lower in the east. This suggests that the western higher-altitude areas were more sensitive to climatic change than were the eastern lower-altitude areas. Holocene climatic records in the Dunde and Guliya ice cores do not correspond. Inverse δ¹⁸O variations between the two cores indicate that the effects of climate and atmospheric processes on the stable isotopes at the two sites differed. The correlation between the isotopic composition of carbonates in lake deposits in western China and climatic variations is similar to that in the ice cores. The climatic resolution in ice cores and lake sediments is higher than that in other media. The lack of precise correspondence of climatic records constructed on the basis of proxy data from different parts of China is a result of the different locations and elevations of the sampling sites, the different resolutions of the source material, and the varied climatic conditions within China. Further work is needed to confirm both the conclusions and the inferences presented here.     

IGU study group on recent climatic change

IGU-Reports

IGU study group on development in highlands and high latitude zones     

Gigantic volcanic eruptions and climatic change in the early Eocene

23 layers of altered volcanic ash (bentonites) originating from the North Atlantic Igneous Province have been recorded in early Eocene deposits of the Austrian Alps, about 1,900 km away from the source area. The Austrian bentonites are distal equivalents of the “main ash-phase” in Denmark and the North Sea basin. We have calculated the total eruption volume of this series as 21,000 km³, which occurred in 600,000 years. The most powerful single eruption of this series took place 54.0 million years ago (Ma) and ejected ca. 1,200 km³ of ash material, which makes it one of the largest basaltic pyroclastic eruptions in geological history. The clustering of eruptions must have significantly affected the incoming solar radiation in the early Eocene by the continuous production of stratospheric dust and aerosol clouds. This hypothesis is corroborated by oxygen isotope values, which indicate a global decrease of sea surface temperatures between 1 and 2°C during this major phase of explosive volcanism.     

Recent climatic change and unusual weather in the Northern Hemisphere

Occurrence frequency of unusual weather caused by anomalous synoptic patterns has its peaks in the middle latitude regions and the subtropical regions. Height anomaly patterns at the 500 mb level for the last three decades show the expansion of negative area in the northern hemisphere, resulting in increase of variability in space and time.     

Holocene climatic change in the northern Midwest: Pollen-derived estimates

Mapping of Holocene pollen data in the midwestern United States has revealed several broadscale vegetational changes that can be interpreted in climatic terms. These changes include (1) the early Holocene northward movement of the spruce-dominated forest and its later southward movement after 3000 yr B.P. and (2) the eastward movement of the prairie/forest border into southwestern Wisconsin by 8000 yr B.P. and its subsequent westward retreat after 6000 yr B.P. When certain basic assumptions are met, multiple regression models can be derived from modern pollen and climate data and used to transform the pollen record of these vegetational changes into quantitative estimates of temperature or precipitation. To maximize the reliability of the regression equations, we followed a sequence of procedures that minimize violations of the assumptions that underlie regression analysis. Reconstructions of precipitation during the Holocene indicated that from 9000 to 6000 yr B.P. precipitation decreased by 10 to 25% over much of the Midwest, while mean July temperature increased by 0.5° to 2.0°C. At 6000 yr B.P. precipitation was less than 80% of its modern values over parts of Wisconsin and Minnesota. After 6000 yr B.P. precipitation generally increased, while mean July temperature decreased in the north, and increased in the south. The time of the maximum temperature varies within the Midwest and is earlier in the north and later in the south.