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Observed Climate Variation and Change

Introduction

This section focuses on changes and variations in the modern climate record. To gain a longer term perspective and to provide a background to the discussion of the palaeo-analogue forecasting technique in Section 3, variations in palaeo-climate also described. Analyses of the climate record can provide important information about natural climate variation and variability. A major difficulty in using observed records to make deductions about changes resulting from resent increases in greenhouse gases in the existence of natural climatic forcing factors that may add to, or subtract from, such changes. Unforced internal variability of the climate system will also occur, further obscuring any signal induced by greenhouse gases. Observing the weather, and converting weather data to information about climate and climate changes, is a very complex endeavour. Virtually all our information about modern climate has been derived from measurements which were designed to monitor weather rather than climate change. Even greater difficulties arise with the proxy data (natural records of climate-sensitive phenomena, mainly pollen remains, lake varves and ocean sediments, insect and animal remains glacier termini) which must be used to deduce the characteristics of climate before the modern instrumental period began. So special attention is given to a critical discussion of the quality of the data on climate change and variability and our confidence in making deductions from these data. Note that we have not made much use of several kinds of proxy data, for example tree ring data, that can provide information on climate change over the last millennium. We recognize that these data have an increasing potential; however their indications are not yet sufficiently easy to assess nor sufficiently integrated with indications from other data to be used in this report. A brief discussion of the basic concepts of climate, climate change, climate trends etc, together with references to material containing more precise definitions of terms, is found in the Introduction at the beginning of this Report.

Palaeo-Climatic Variations and Change

Climate Of The Past 5,000,000 Years

Climate varies naturally on all time scales from hundreds of millions of years to a few years. Prominent in recent Earth`s history have been the 100,000 year Pleistocene glacial –interglacial cycles when climate was mostly cooler than at present. This period began about 2,000,000 years before the present time and was preceded by a warmer epoch having only limited glaciations, mainly over Antarctica, called the Pliocene. Global surface temperatures have typically varied by 5-7 °C through the Pleistocene ice age cycles, with large changes in ice volume and sea level, and temperature variations as great as 10-15 °C in some middle and high latitude regions of the Northern Hemisphere. Since the beginning of the current interglacial epoch about 10,000 BP, global temperatures have fluctuated within a much smaller range. Some fluctuations have nevertheless lasted several centuries, including the Little Ice Age which ended in the nineteenth century and which was global in extent.Proxy data clearly indicate that the Earth emerged from the last ice age 10,000 to 15,000 BP. During this glacial period continental-size ice sheets covered much of North America and Scandinavia, and world sea level was about 120m below present values. An important cause of the recurring glaciations is believed to be variations in seasonal radiation receipts in the Northern Hemisphere. These variations are due to small changes in the distance of the Earth from the sun given seasons, and slow changes in the angle of the tilt of the Earth`s axis which affects the amplitude of the seasonal insolation. These “Milankovitch” orbital effects appear to be correlated with the glacial-interglacial cycle since glacials arise when solar radiation is least in the extratropical Northern Hemisphere summer. Variations in carbon dioxide and methane in ice age cycles are also very important factors; they served to modify and perhaps amplify the other forcing effects. However, there is evidence that rapid changes in climate have occurred on the time scales of about a century which cannot be directly related to orbital forcing or to changes in atmospheric composition. The most dramatic of these events was the Younger Dryas cold episode which involved an abrupt reversal of the general warming trend in progress around 10,500 BP as the last episode of continental glaciations came to close. The Younger Dryas was an event of global significance; it was clearly observed in New Zealand though its influence may not have extended to all parts of the globe. There is, as yet, no consensus on the reasons for this climatic reversal, which lasted about 500 years and ended very suddenly. However, because the signal was strongest around the North Atlantic Ocean, suggestions have been made that the climatic reversal and its physical origin in large changes in the sea surface temperature (SST) of the Laurentide Ice sheet and the resulting influx of huge amounts of low density freshwater into the northern North Atlantic ocean( Broecker et al ., 1985). Consequential changes in the global oceanic circulation may have occurred (Street – Perrott and Perrott, 1990) which may have involved variations in the strength of the terhmohaline circulation in the Atlantic. This closed oceanic circulation involved northward flow of water near the ocean surface, sinking in the sub- Arctic and a return flow at depth. The relevance of the Younger Dryas to today’s conditions is that it is possible that changes in the thermohaline circulation of a qualitatively similar character might occur quite quickly during a warming of the climate induced by greenhouse gases. A possible trigger might be an increase of precipitation over the extra tropical North Atlantic (Broecker , 1987), though the changes in ocean circulation are most likely to be considerably smaller that in the Yonger Dryas . Section 6 gives further details.The period since the end last glaciation has been characterized by small change in global average temperature with a range of probably less that 2°C (Figure 7.1), thought it is still not clear weather all the fluctuations indicated were truly global. However, large regional changes in hydrological conditions have occurred, particularly in the tropics. Weather conditions in the Sahara from 12.000 to 4. 000 years BP enabled cultural groups to survive by hunting and fishing in what are today almost the most arid regions on Earth. During this time Lake Chad expanded to become as large as the Caspian Sea is today (several hundred thousand km2, Grove and Warren , 1968).Drier conditions became established after 4.000 BP and many former lake basins became completely dry (Street-Perrot and Harrison , 1985). Pollen sequences from lake beds of northwest India suggest during the recent glacial maximum (Singh et al., 1974), but the epoch 8.000 to 2.500 BP experienced a humid climate with frequent floods.There is growing evidence that worldwide temperatures were higher that at present during the mid-Holocene (especially 5.000-6.0000 BP), at least in summer, though carbon dioxide levels appear to have been quite similar to those of western Europe , China, Japan, the eastern UAS were a few degrees warmer in July during the mid-Holocene that in recent decades (Yoshino and Urushibara. 1978; Webb et al,. 1987;Huntley and Prentice, 1988;Zhang and Wang, 1990).Parts of Australasia and Chile were also warmer. The late tenth to early thirteenth centuries (about AD 950- 1250) appear to have been exceptionally warm in western Europe, Iceland and Greenland (Alexandre 1987; Lamb, 1988).This period is known as the Medieval Climatic Optimum. China was, however, cold at this time (mainly in winter) but South Japan was warm (Yoshino, 1978).This period of widespread warmth is notable in that there is no evidence that it was accompanied by an increase of greenhouse gases.Cooler episodes have been associated with glacial advances in alpine regions of the world; such ’neo-glacial’ episodes have been increasingly common in the last few thousand years. Of particular interest is the most recent cold event, the ‘Little Ice Age’, which resulted in extensive glacial advances in almost all alpine regions of the world between 150 and 450 years ago (Grove, 1988) so that glaciers were more extensive 100-200 years ago that now nearly everywhere (Figure 7.2). Although not a period of continuously cold climate, the Little Ice Age was probably the coolest and most globally-extensive cool period since the Younger Dryas. Ina few regions, alpine glaciers advanced down-valley even further that during the last glaciations ( for example Hammer, 1977; Porter, 1986);others claim a connection between glacier advances such as the Maunder and Sporer solar activity minima (Eddy,1976), but see also Pittock (1983).At present, there is no agreed explanation for these recurrent cooler episodes.The Little Ice Age came to an end only in the nineteenth century.Thus some of the global warming since 1850 could be a recovery from the Little Ice Age rather than a direct result of human activities.So it is important to recognize that natural variations of climate are appreciable and will modulate any future changes induced by man.

Palaeo-Climate Analogues from Three Warm Epochs

Three periods from the past have been suggested by Budyko and Izrael (1987) as analogues of a future warm climate. For the second and third periods listed below, however, it can be argued that the changed seasonal distribution of incoming solar radiation existing at those times may not necessarily have produced the same climate as would result from a globally-averaged increase in greenhouse gases. 1) The climate optimum of the Pliocene (about 3,300,000 to 4,300,000 years BP), 2) The Eemian interglacial optimum (125,000 to 130,000 years BP), 3) The mid-Holocene (5,000 to 6,000 years BP). Note that the word “optimum” is used here for convenience and is taken to imply a warm climate. However such a climate may not be ”optimal” in all senses.

Pliocene climatic optimum (about 3,300,000 to 4,300,000 BP)

Reconstructions of summer and winter mean temperatures and total annual precipitation have been made for this period by scientists in the USSR. Many types of proxy data were used to develop temperature and precipitation patterns over the land masses of the Northern Hemisphere (Budyko and Izrael,1987).Over the oceans, the main sources of information were cores drilled in the bed of the deep ocean by the American Deep-sea Ocean Core Drilling Project. Some of these reconstructions are shown in Figure7.3 a and b. Figure 7.3a suggest that mid-latitude Northern Hemisphere summer temperatures averaged about 3-4°C higher than present-day values. Atmospheric concentrations of carbon dioxide are estimated by Budyko et al.(1985) to have been near 660 ppm, i.e., twice as large as immediately pre-industrial values. However Berner et al.(1983) show lower carbon dioxide concentrations. So there is some doubt about the extent to which atmospheric carbon dioxide concentrations were higher than present values during the Pliocene. Figure 7.3b is a partial reconstruction of Northern Hemisphere annual precipitation; this was generally greater during the Pliocene. Of special interest is increased annual precipitation in the arid regions of Middle Asia and Northern Africa where temperatures were lower than at present in summer.Uncertainties associated with the interpretation of these reconstructions are considerable and include: 1) Imprecise dating of the records, especially those from the continents (uncertainties of 100,000 years or more ); 2) Differences from the present day surface geography, including changes in topography; thus Tibet was at least 100m lower than now and the Greenland ice sheet may have much smaller; 3) The ecology of life on Earth from which many of the proxy data are derived was significantly different.

Eemian interglacial optimum (125,000 – 130, 000 years BP )

Palaeo-botanic, oxygen-isotope and other geological data show that the climates of the warmest parts of some of the Pleistocene interglacials were considerably warmer (I to 2° C) than the modern climate. They have been considered as analogues of future climate (Budyko and Izrael, 1987; Zubakov and Borzenkova, 1990). Atmospheric carbon dioxide reached about 300 ppm during the Eemian optimum (Section 1 ) but a more a more important cause of the Earth’s orbit around the sun was about twice the modern value, giving markedly more radiation in the northern hemisphere summer. The last interglacial optimum (125,000- 130,000 years BP ) has sufficient information (Velichko et al., 1982, 1983, 1984 and CLIMAP, 1984 ) to allow quantitative reconstructions to be made of annual and seasonal air temperature and annual precipitation for part of the Northern Hemisphere. For the Northern Hemisphere as a whole , mean annual surface air temperature was about 2°C above its immediately pre-industrial value. Figure 7.4 shows differences of summer air temperature , largest (by 4-8°C) in northern Siberia , Canada and Greenland . Over most of the USSR and Western Europe north of 50 – 60 ° N, temperatures were about 1-3°C warmer than present. South of these areas , temperatures were similar to those of today ,and precipitation was substantially larger over most parts of the continents of the Northern Hemisphere . In individual regions of Western Europe, the north of Eurasia and Soviet Central Asia and Kazakhstan, annual precipitation has been estimated to have been 30-50 % higher than modern values.

It is difficult to assess quantitatively the uncertainties associated with these climate reconstructions .The problems include;

1) Variations between the timing of the deduced thermal maximum in different records; 2) The difficulties of obtaining proxy data in aird areas; 3) The absence of data from North America and many other continental regions in both Hemispheres.

Climate of the Holocene Optimum (5,000-6,000 years BP )

The Early and Middle Holocene was characterized by a relatively warm climate with summer temperatures in high northern latitudes about 3-4°C above modern values. Between 9,000 and 5,000 years BP there were several short-lived warm epochs, the last of which , the mid Holocene optimum , lasted from about 6,200 to 5,300 years BP ( Varushehenko et al., 1980). Each warm epoch was accompanied by increased precipitation and higher lake levels in subtropical and high latitudes (Singh et al., 1974; Swain et al., 1983).However, the level of such mid latitude lakes as the USA was lowered (COHMAP, 1988; Borzenkova and Zubakov 1984).

Figures 7.5a and b show maps of summer surface air temperature ( as departures from immediately pre – industrial values) and annual precipitation for the mid-Holocene optimum in the Northern Hemisphere. This epoch is sometimes used as an analogue of expected early – 21 st century climate. The greatest relative warmth  summer (up to 4° C ) was in high latitudes north of 70° N ( Lozhkin and Vazhenin , 1987 ). In middle latitudes, summer temperatures were often 1-2°C higher and further south  summer temperatures were often lower than today , for example in Soviet Central Asia, the Sahara , and Arabia. These areas also had increased annual precipitation. Annual precipitation was about 50-100 mm higher than at present in the Northern regions of Eurasia and Canada but in central regions of Western Europe and in southern regions of the European USSR and West Siberia there were small decreases of annual precipitation. The largest decrease in annual precipitation took place in USA, especially in central and eastern regions (COHMAP , 1988).The above reconstructions are rather uncertain; thus Figure 7.5a disagrees with reconstructions of temperature over north east Canada given by Bartlein and Webb (1985).However the accuracy of reconstructions is increasing as more detailed information for individual regions in both hemispheres becomes available. For instance, the CLIMANZ project has given quantitative estimates of Holocene temperature and precipitation in areas from New Guinea to Antarctica for  selected times (Chappell and  Grindord, 1983).Detailed mid- Holocene reconstructions of summer temperature in Europe and China are shown in Figure 7.5c.

The Modern Instrumental Record

The clearest signal of an enhanced greenhouse effect in the climate system , as indicated by atmosphere/ocean general circulation models, would be a widespread, substantial increase of near-surface temperatures. This section gives special attention to variations and changes of land surface air temperatures (typically measured at about two meters above the ground surface) and sea surface temperatures (SSTs) since the mid-nineteenth century. Although earlier temperature, precipitation, and surface pressure data are available (Lamb, 1977), spatial coverage is very poor. We focus on changes over the globe and over the individual hemispheres but considerable detail on regional space scales is also given.

Surface Temperature Variations and Change

Hemisphere and Global Land

Three research groups (Jones et al., 1986a,b;Jones, 1988;Hansen and Lebedeff, 1987, 1988; and Vinnikov et al., 1987, 1990) have produced similar analyses of hemispheric land surface air temperature variations (Figure 7.6) from broadly the same data. All three analyses indicate that during the last decade globally-averaged land temperatures have been higher than in any decade in the past 100 to 400 years. (The smoothed lines in Figure 7.6, as for all the longer time series shown in this Section, are produced by a low pass binomial filter with 21 terms operating on the annual data. The filter passes fluctuations having a period of 20 years or more almost unattenuated).Figure 7.6 shows that temperature increased from the relatively cool late nineteenth century to the relatively warm 1980s, but the pattern of change differed between the two hemispheres. In the Northern Hemisphere the temperatures changes over land are irregular and an abrupt warming of about 0.3°C appears to have occurred during the early 1920s. This climatic discontinuity has been pointed out by Ellsaesser et al. (1986) in their interpretation of the thermometric record. Northern Hemisphere temperatures prior to the climatic discontinuity in the 1920s could be interpreted as varying about a stationary mean climate as shown by the smoothed curve. The nearest approach to a monotonic trend in the Northern Hemisphere time series is the decrease of temperature from the late 1930s to the mid- 1960s of about 0.2°C. The most recent warming has been dominated by a relatively sudden increase of nearly 0.3°C over less than ten years before 1982. Of course, it is possible to fit a monotonic trend line to the entire time series; such a trend fitted to the current version of the Jones (1988) data gives a rate of warming of 0.53°C/100 years when the trend is calculated from 1881 to 1989 or the reduced, if less reliable, value of 0.45°C/100 years if it is calculated from 1861. Clearly, this is a gross oversimplification of the observed variations, even though the computed linear trends are highly significant in a statistical sense.The data for the Southern Hemisphere include the Antarctic land mass, since 1957, except for the data of Vinnikov et al. (1987, 1990). Like the Northern Hemisphere, the climate appears stationary throughout the latter half of the nineteenth century and into the early part of the twentieth century. Subsequently, there is an upward trend in the data until the late 1930s, but in the next three decades the mean temperature remains essentially stationary again. A fairly steady increase of temperature resumes before 1970, though it may have slowed recently. Linear trends for the Southern Hemisphere are 0.52°C/100 years from 1881 to 1989, but somewhat less, and less reliable, at 0.45°C/100 years for the period 1861-1989. The interpretation of the rise in temperature shown in Figure 7.6 is a key issue for global warming, so the accuracy of these data needs careful consideration. A number of problems may have affected the record, discussed in turn below: 1) Spatial coverage of the data is incomplete and varies greatly; 2) Changes have occurred in observing schedules and practices; 3) Changes have occurred in the exposures of thermometers; 4) Stations have changed their locations; 5) Changes in the environment, especially urbanization, have taken place around many stations. Land areas with sufficient data to estimate seasonal anomalies of temperature in the 1860s and 1980s are shown ( with ocean areas ) in Figure 7.7. Decades between these times have an intermediate coverage. There are obvious gaps and changes in coverage. Prior to 1957, data for Antarctica are absent while some other parts of the global land mass lack data as late as the 1920s, for example many parts of Africa, parts of China, the Russian and Canadian Arctic, and the tropics of South America. In the 1860s coverage is sparsest; thus Africa has little or no data and much of North America is not covered. The effect or this drastically changing spatial coverage on hemispheric temperature variations has been tested by Jones et al. (1986a, b) who find that sparse spatial coverage exaggerates the variability of the Northern Hemisphere annual time series after about 1880 (Figure 7.6) is attributed to this effect. Remarkably, their analyses using a “frozen grid” experiment (see Section 7.4.1.3 for a detailed discussion for the combined land and ocean data) suggest that changes of station density since 1900 have had relatively little impact on estimates of hemispheric land temperature anomalies. However, prior to 1900, the decadal uncertainty could be up to 0.1°C. This is quite small relative to the overall change. Thus varying data coverage does not seem to have had a serious impact on the magnitude of the perceived warming over land over the last 125 years.Another potential bias arises from changes in observation schedules. Even today, there is no international standard for the calculation of mean daily temperature. Thus each country calculates mean daily temperature by a method of its choice, such as the average of the maximum and the minimum, or some combination of hourly readings weighted according to a fixed formula. As long as each country continues the same practice, the shape of the temperature record is unaffected. Unfortunately, few countries have maintained the same practice over the past century; biases have therefore been introduced into the climate record, some of which have been corrected for in existing global data sets, but some have not. These biases can be significant; in the USA a systematic change in observing times has led to a nominal 0.2°C decrease of temperature in the climate record since the 1930s (Karl et al., 1986). The effects of changing observation time have only been partly allowed for in the USA temperature data used in analyses presented here. So an artificial component of cooling of rather less than 0.2°C may exist in the USA part of the temperature analyses for this reason, offsetting the warming effects of increasing urbanization in that country. Artificial changes of temperature of either sign may exist in other parts of the world due to changes in observation time but have not been investigated.Substantial systematic changes in the exposure of thermometers have occurred. Because thermo-meters can be affected by the direct rays of the sun, reflected solar radiation, extraneous effort to improve their exposures over the last 150 years. Additional biases must accompany these changes in a thermometric record. Since many of the changes in exposure took place during the nineteenth and early twentieth centuries, that part of the record is most likely to be affected. Recently, Parker (1990) has reviewed the earlier thermometer exposures, and how they evolved, in many different countries. The effects of exposure changes vary regionally (by country) and seasonally. Thus tropical temperatures prior to the late 1920s appear to be too high because of the placement of thermometers in cages situated in open sheds. There is also evidence that for the mid –latitudes prior to about 1880 summer temperatures may be too high and winter temperatures too low due to use of poorly screened exposures. This includes the widespread practice of exposing thermometers on the north walls of buildings. These effects have not yet been accounted for in existing analyses (see Section 7.4.2.2).Changes in station environment can seriously affect temperature records (Salinger, 1981). Over the years, stations often have minor (usually under 10 km) relocations and some stations have been moved from rooftop to ground level. Even today, international practice allows for a variation of thermometer heights above ground from 1.25 to 2 meters. Because large vertical temperature gradients exist near the ground, such changes could seriously affect thermometer records. When relocations occur in a random manner, they do not have a serious impact on hemispheric or global temperature anomalies, though they impair our ability to develop information about much smaller scale temperature variations. A bias on the large scale can emerge when the character of the change is not random. An example is the systematic relocations of some observing stations from inside cities in many countries to more rural airport locations that occurred several decades ago. Because of the heat island effect within cities, such moves tend to introduce artificial cooling into the climate record. Jones et al. (1986a, b ) attempt in some detail to adjust for station relocations when these appear to have introduced a significant bias in the data but Hansen and lebedeff (1988) do not , believing that such station moves cancel out over large time and space averages. Vinnikov et al. (1990) do adjust for some of these moves. There are several possible correction procedures that have been, or could be, applied to the Jones (1988) data set (Bradley and Jones, 1985 ; Karl and Williams , 1987). All depend on denser network of stations than are usually available except in the USA, Europe, the Western Soviet Union and a few other areas. Of the above problems, increasing urbanization around fixed stations is the most serious source of systematic error for hemispheric land temperature time series that has so far been identified. A number of researchers have tried to ascertain the impact of urbanization on the temperature record. Hansen and Lebedeff (1987) found that when they removed all stations having a population in 1970 of greater than 100,000, the trend of temperature was reduced by 0,1°C over 100 years. They speculated that perhaps an additional 0,1°C of bias might remain due to increases in urbanisation around stations in smaller cities and towns. Jones et al. (1989) estimate that the effect of urbanization in their quality-controlled data is no more than 0,1 ° Cover the past 100 years. This conclusion is based on a comparison of their data with a dense network of mostly rural stations over the USA . Groisman and Koknaeva (1990) compare the data from Vinnikov et al. (1990) with the rural American data set and with rural station in the Soviet Union and find very small warm relative biases of less than 0.05 °C per 100 years. In the USA, Karl et al. (1988) find that increases due to urbanization can be significant (0,1°C) , even When urban areas have populations as low as 10,000. Other areas of globe are now being studied. Preliminary results indicate that the effects of urbanization are regional and time dependent. Changes in urban warming in China (Wang et al. 1990) appear to be quite large over the past decade, but in Australia they are rather less than is observed in the USA (Coughlan et al., 1990). Recently , Jones and coworkers (paper in preparation) have compared trends derived from their quality –controlled data, and those of Vinnikov et al. (1990), with specially selected data from more ritual stations in the USSR, eastern China, and Australia. When compared with trends from the more ritual stations, only small (positive) differences of temperature exist in the data used in Jones (1988) and Vinnikov et al. (1990) in Australia and the USSR (of magnitude less than 0.05°C/100 years). In eastern China, the data used by Vinnikov et al. (1990) and Jones (1988) give smaller warming trends than those derived from more ritual stations. This is an unexpected result. It suggest that either (1) the more rural set is sometimes affected by urbanization or, (2) other changes in station characteristics over-compensate for urban warming bias. Thus it is known that the effects of biases due to increased urbanization in the Hansen and Lebedeff (1987) and the Vinnikov et al. (1990) data sets are partly offset by the artificial cooling introduced by the movement of stations from city centers to more rural airport locations during the 1940s to 1960s (Karl and Jones, 1990). Despite this, some of these new rural airport locations may have suffered recently from increasing urbanization.In light of this evidence, the estimate provided by Jones et al. (1989) of a maximum overall warming bias in all three land data sets due to urbanization of 0.1°C/100 years, or less, is plausible but not conclusive.

Sea

The oceans comprise about 61% of the Northern Hemisphere and 81% of the Southern Hemisphere. Obviously, a compilation of global temperature variations must include ocean temperatures. Farmer et al. (1989) and Bottomley et al. (1990) have each created historical analyses of global ocean SSTs which are derived mostly from observations taken by commercial ships. These data are supplemented by weather ship data and, in recent years, by an increasing number of drifting and moored buoys. The farmer et al. (1989) analyses are derived from a collection of about 80 million observations assembled in the Comprehensive Ocean-Atmosphere Data Set (COADS) in the USA (Woodruff et al., 1987). The data set used by Bottomley et al. (1990) is based on a slightly smaller collection of over 60 million observations assembled by the United Kingdom Meteorological Office. Most, but not all, of the observations in the latter are contained in the COADS data set.Long-term variations of SSTs over the two hemispheres, shown in Figure 7.8, have been, in general, similar to their land counterparts. The increase in temperature has not been continuous. There is evidence for a fairly rapid cooling in SST of about 0.1 to 0.2°C at the beginning of the twentieth century in the Northern Hemisphere. This is believed to be real because night marine air temperatures show a slightly larger cooling. The cooling strongly affected the North Atlantic, especially after 1903, and is discussed at length by Helland-Hansen and Nansen (1920). The cool period was terminated by a rapid rise temperature starting after 1920. This resembled the sudden warming of land temperatures, but lagged it by several years. Subsequent cooling from the late 1950s to about 1975 lagged that over land by about five years, and was followed by renewed warming with almost no lag compared with land data. Overall warming of the Northern Hemisphere oceans since the late nineteenth century appears to have been slightly smaller than that of the land (Figure 7.8a), and may not have exceeded 0.3°C. In the Southern Hemisphere ocean (remembering that the Southern Ocean has always been poorly measured) there appear to have been two distinct stable climatic periods, the first lasting until the late 1920s, the second lasting from the mid-1940s until the early 1960s. Since the middle 1970s, SSTs in the Southern Hemisphere have continued to rise to their highest levels of record. Overall warming has certainly exceeded 0.3°C since the nineteenth century, but has probably been less than 0.5°C (Figure 7.8b),and has been slightly less than the warming of the land. However, if the increases of temperature are measured from the time of their minimum values around 1910, the warming of the oceans has been slightly larger than that of the land. Despite data gaps over the Southern Ocean, the global mean ocean temperature variations (Figure 7.9) tend to take on the characteristics of the Southern Hemisphere because a lager area of ocean is often sampled in the Southern Hemisphere than the Northern Hemisphere. Overall warming in the global oceans between the late nineteenth century and the latter half of the twentieth century appears to have been about 0.4 °C. Significant differences between the two SST data sets presented in Figure 7.8 result mainly from differing assumptions concerning the correction of SST data for instrumental biases. The biases arose chiefly from changes in the method of sampling the sea water for temperature measurement. Several different types of bucket have been used for sampling made , for example , of wood , canvas , rubber or metal , but the largest bias arose from an apparently rather sudden transition from various uninsulated buckets to ship engine intake tubes in World War II. A complex correction procedure developed by Folland and Parker ( 1989 ) and Bottomley et al. ( 1990), which creates geographically varying corrections, has been also been used in nearly the same form by Farmer et al. Differences in the two data sets remain, however , primarily because of different assumptions about the mix of wooden versus canvas buckets used during the nineteenth century. Despite recommendations by Maury (1858) to use wooden buckets with the thermometer inserted for four to five minutes, such buckets may have been much less used in practice (Toynbee, 1874; correspondence with the Danish Meteorological Service , 1989) possibly because of damage iron-banded wooden buckets could inflict upon the hulls of ships. Some differences also result, even as recently as the 1970s, because the data are not always derived from identical sources (Woodruff, 1990).No corrections have been applied to the SST data from 1942 to date. Despite published discussion about the differences between ‘’bucket’’ and engine intake SST data in this period ( for example James and Fox , 1972) , there are several reasons why it is believed that no further correction, with one reservation noted below, are needed. Firstly the anomalies in Figure 7.8 are calculated from the mean conditions in 1951- 1980. So only relative changes in the mix of data since 1942 are important. Secondly many of the modern ‘’ buckets ‘’ are insulated ( Folland and Parker, 1990) so that they cool much less that canvas buckets. A comparison of about two million bucket and four million engine intake data for 1975 – 1981 ( Bottomley et al., 1990) reveals a global mean difference of only 0.08°C, the engine intake data begin the warmer. Thus a substantial change in the mix of data types ( currently about 25- 30 % buckets) must occur before an appreciable artificial change will occur in Figure 7.8. This conclusion is strongly supported by the great similarity between time series of globally-averaged anomalies of collocated SST and night marine air temperature data from 1955 to date ( not shown ). Less perfect agreement between 1946 and the early 1950s (SST colder) suggest that uninsulated bucket SST data may have been more numerous then than 1951-80, yielding an overall cold bias of up to 0.1°C on a global average.Marine air temperatures are a valuable test of the accuracy of SSTs after the early 1890s. Biases of day-time marine air temperatures are so numerous and difficult to overcome that only night-time marine air temperatures have been used. The biases arise during the day because overheating of the thermometers and screens by solar insolation has changed as ships have changed their physical characteristics (Folland et al., 1984). On the other hand appreciable biases of night-time data are currently believed to be confined to the nineteenth century and much of the Second World War. Night marine air temperatures have been found to be much too high relative to SST, or to modern values, in certain regions and seasons before 1894 (Bottomley et al., 1990). These values were corrected using SSTs, but subsequently (except in 1941-1945) night marine air temperature data constitute independent evidence everywhere, although corrections are also made for the increasing heights of ship decks (Bottomley et al., 1990).Figure 7.9 indicates the multi-decadal global variations of quite similar to those of SST. To provide a complete picture, Figure 7.9 shows the Farmer et al. and UK Meteorological Office global SST curves separately along with a global land air temperature series created by averaging the series of Jones, Hansen and Lebedeff and Vinnikov et al. Both SST and night marine air temperature data appear to lag the land data by at least five years during the period of warming from 1920 to the 1940s. However some of the apparent warmth of the land at this time may be erroneous due to the use of open shed screens in the tropics (Section 7.4.1.1).The above results differ appreciably in the nineteenth century from those published by Oort et al. (1987) who followed the much less detailed correction procedure of Folland (1984) to adjust the COADS SST and all hours marine air temperature data sets. Newell et al.(1989) also present an analysis, quite similar to that of the above authors, based on a UK Meteorological Office data set that was current in early 1988. All these authors obtain higher values of global SST and marine air temperature in the middle to late nineteenth century, typically by about 0.1°C and 0.15°C respectively, than are indicated in this report. It is our best judgement that the more recent analyses represent a real improvement, but the discrepancies highlight the uncertainties in the interpretation of early marine temperature records. Yamamoto et al. (1990a) have tried to quantify changing biases in the COADS all hours marine air temperature data using a mixture of weather ship air temperature data from the 1940s to 1970s and selected land air temperature data, mainly in the three tropical coastal regions, to calculate time varying corrections. Based on these corrections, Yamamoto et al. (1990b) calculate a global air temperature anomaly curve for 1901-1986 of similar overall character to the night marine air temperature curve in Figure 7.9 but with typically 0.15°C warmer anomalies in the early part of the twentieth century, and typically 0.1°C cooler anomalies, in the warm period around 1940-1950. Recent data are similar. It could be argued that the corrections of Yamamoto et al. may be influenced by biases in the land data, including warm biases arising from the use of tropical open sheds earlier this century. Warm biases may also exist in some ocean weather ship-day air temperature data (Folland, 197). Although we believe that the night marine air temperature analysis in Figure 7.9 minimises the known sources of error, the work of Yamamoto et al. underlines the level of uncertainty that exists in trends derived from marine air temperature data. Geography (from Greek Error: {{Lang}}: text has italic markup (help) - geographia, lit. "earth describe-write") is the science that deals with the study of the Earth and its lands, features, inhabitants, and phenomena. A literal translation would be "to describe or write about the Earth". The first person to use the word "geography" was Eratosthenes (276-194 BC). Four historical traditions in geographical research are the spatial analysis of natural and human phenomena (geography as a study of distribution), area studies (places and regions), study of man-land relationship, and research in earth sciences. Nonetheless, modern geography is an all-encompassing discipline that foremost seeks to understand the Earth and all of its human and natural complexities—not merely where objects are, but how they have changed and come to be. Geography has been called 'the world discipline'. As "the bridge between the human and physical sciences," geography is divided into two main branches—human geography and physical geography.

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Introduction

Traditionally, geographers have been viewed the same way as cartographers and people who study place names and numbers. Although many geographers are trained in toponymy and cartology, this is not their main preoccupation. Geographers study the spatial and temporal distribution of phenomena, processes and features as well as the interaction of humans and their environment. As space and place affect a variety of topics such as economics, health, climate, plants and animals, geography is highly interdisciplinary.

...mere names of places...are not geography...know by heart a whole gazetteer full of them would not, in itself, constitute anyone a geographer. Geography has higher aims than this: it seeks to classify phenomena (alike of the natural and of the political world, in so far as it treats of the latter), to compare, to generalize, to ascend from effects to causes, and, in doing so, to trace out the laws of nature and to mark their influences upon man. This is 'a description of the world'—that is Geography. In a word Geography is a Science—a thing not of mere names but of argument and reason, of cause and effect.

— William Hughes, 1863

Geography as a discipline can be split broadly into two main subsidiary fields: human geography and physical geography. The former focuses largely on the built environment and how space is created, viewed and managed by humans as well as the influence humans have on the space they occupy. The latter examines the natural environment and how the climate, vegetation & life, soil, water, and landforms are produced and interact. As a result of the two subfields using different approaches a third field has emerged, which is environmental geography. Environmental geography combines physical and human geography and looks at the interactions between the environment and humans.

Branches

Physical geography

Physical geography (or physiography) focuses on geography as an Earth science. It aims to understand the physical problems and issues of : lithosphere, hydrosphere, atmosphere, pedosphere, and global flora and fauna patterns (biosphere). Physical geography can be divided into the following broad categories:

Biogeography	Climatology & paleoclimatology	Coastal geography	Env. geog. & management
Geodesy	Geomorphology	Glaciology	Hydrology & Hydrography
Landscape ecology	Oceanography	Pedology	Palaeogeography
Quaternary science

Human geography

Human geography is a branch of geography that focuses on the study of patterns and processes that shape human interaction with various environments. It encompasses human, political, cultural, social, and economic aspects. While the major focus of human geography is not the physical landscape of the Earth (see physical geography), it is hardly possible to discuss human geography without referring to the physical landscape on which human activities are being played out, and environmental geography is emerging as a link between the two. Human geography can be divided into many broad categories, such as:

Cultural geography	Development geography	Economic geography	Health geography
Historical & Time geog.	Political geog. & Geopolitics	Pop. geog. or Demography	Religion geography
		File:Tourists-2-x.jpg
Social geography	Transportation geography	Tourism geography	Urban geography

Various approaches to the study of human geography have also arisen through time and include:

• Behavioral geography
• Feminist geography
• Culture theory
• Geosophy

Environmental geography

Environmental geography is the branch of geography that describes the spatial aspects of interactions between humans and the natural world. It requires an understanding of the traditional aspects of physical and human geography, as well as the ways in which human societies conceptualize the environment.

Environmental geography has emerged as a bridge between human and physical geography as a result of the increasing specialisation of the two sub-fields. Furthermore, as human relationship with the environment has changed as a result of globalization and technological change a new approach was needed to understand the changing and dynamic relationship. Examples of areas of research in environmental geography include emergency management, environmental management, sustainability, and political ecology.

Geomatics

Geomatics is a branch of geography that has emerged since the quantitative revolution in geography in the mid 1950s. Geomatics involves the use of traditional spatial techniques used in cartography and topography and their application to computers. Geomatics has become a widespread field with many other disciplines using techniques such as GIS and remote sensing. Geomatics has also led to a revitalization of some geography departments especially in Northern America where the subject had a declining status during the 1950s.

Geomatics encompasses a large area of fields involved with spatial analysis, such as Cartography, Geographic information systems (GIS), Remote sensing, and Global positioning systems (GPS).

Regional geography

Regional geography is a branch of geography that studies the regions of all sizes across the Earth. It has a prevailing descriptive character. The main aim is to understand or define the uniqueness or character of a particular region which consists of natural as well as human elements. Attention is paid also to regionalization which covers the proper techniques of space delimitation into regions.

Regional geography is also considered as a certain approach to study in geographical sciences (similar to quantitative or critical geographies, for more information see History of geography).

Related fields

• Urban planning, regional planning and spatial planning: use the science of geography to assist in determining how to develop (or not develop) the land to meet particular criteria, such as safety, beauty, economic opportunities, the preservation of the built or natural heritage, and so on. The planning of towns, cities, and rural areas may be seen as applied geography.
• Regional science: In the 1950s the regional science movement led by Walter Isard arose, to provide a more quantitative and analytical base to geographical questions, in contrast to the descriptive tendencies of traditional geography programs. Regional science comprises the body of knowledge in which the spatial dimension plays a fundamental role, such as regional economics, resource management, location theory, urban and regional planning, transport and communication, human geography, population distribution, landscape ecology, and environmental quality.
• Interplanetary Sciences: While the discipline of geography is normally concerned with the Earth, the term can also be informally used to describe the study of other worlds, such as the planets of the Solar System and even beyond. The study of systems larger than the earth itself usually forms part of Astronomy or Cosmology. The study of other planets is usually called planetary science. Alternative terms such as Areology (the study of Mars) have been proposed, but are not widely used.

Techniques

As spatial interrelationships are key to this synoptic science, maps are a key tool. Classical cartography has been joined by a more modern approach to geographical analysis, computer-based geographic information systems (GIS).

In their study, geographers use four interrelated approaches:

• Systematic - Groups geographical knowledge into categories that can be explored globally.
• Regional - Examines systematic relationships between categories for a specific region or location on the planet.
• Descriptive - Simply specifies the locations of features and populations.
• Analytical - Asks why we find features and populations in a specific geographic area.

Cartography

Cartography studies the representation of the Earth's surface with abstract symbols (map making). Although other subdisciplines of geography rely on maps for presenting their analyses, the actual making of maps is abstract enough to be regarded separately. Cartography has grown from a collection of drafting techniques into an actual science.

Cartographers must learn cognitive psychology and ergonomics to understand which symbols convey information about the Earth most effectively, and behavioral psychology to induce the readers of their maps to act on the information. They must learn geodesy and fairly advanced mathematics to understand how the shape of the Earth affects the distortion of map symbols projected onto a flat surface for viewing. It can be said, without much controversy, that cartography is the seed from which the larger field of geography grew. Most geographers will cite a childhood fascination with maps as an early sign they would end up in the field.

Geographic information systems

Geographic information systems (GIS) deal with the storage of information about the Earth for automatic retrieval by a computer, in an accurate manner appropriate to the information's purpose. In addition to all of the other subdisciplines of geography, GIS specialists must understand computer science and database systems. GIS has revolutionized the field of cartography; nearly all mapmaking is now done with the assistance of some form of GIS software. GIS also refers to the science of using GIS software and GIS techniques to represent, analyze and predict spatial relationships. In this context, GIS stands for Geographic Information Science.

Remote sensing

Remote sensing is the science of obtaining information about Earth features from measurements made at a distance. Remotely sensed data comes in many forms such as satellite imagery, aerial photography and data obtained from hand-held sensors. Geographers increasingly use remotely sensed data to obtain information about the Earth's land surface, ocean and atmosphere because it: a) supplies objective information at a variety of spatial scales (local to global), b) provides a synoptic view of the area of interest, c) allows access to distant and/or inaccessible sites, d) provides spectral information outside the visible portion of the electromagnetic spectrum, and e) facilitates studies of how features/areas change over time. Remotely sensed data may be analyzed either independently of, or in conjunction with, other digital data layers (e.g., in a Geographic Information System).

Quantitative methods

Geostatistics deal with quantitative data analysis, specifically the application of statistical methodology to the exploration of geographic phenomena. Geostatistics is used extensively in a variety of fields including: hydrology, geology, petroleum exploration, weather analysis, urban planning, logistics, and epidemiology. The mathematical basis for geostatistics derives from cluster analysis, linear discriminant analysis and non-parametric statistical tests, and a variety of other subjects. Applications of geostatistics rely heavily on geographic information systems, particularly for the interpolation (estimate) of unmeasured points. Geographers are making notable contributions to the method of quantitative techniques.

Qualitative methods

Geographic qualitative methods, or ethnographical; research techniques, are used by human geographers. In cultural geography there is a tradition of employing qualitative research techniques also used in anthropology and sociology. Participant observation and in-depth interviews provide human geographers with qualitative data.

History

History of geography
Graeco-Roman Chinese Islamic Age of Discovery History of cartography Historical geography Environmental determinism Regional geography Quantitative revolution Critical geography
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The oldest known world maps date back to ancient Babylon from the 9th century BC. The best known Babylonian world map, however, is the Imago Mundi of 600 BC. The map as reconstructed by Eckhard Unger shows Babylon on the Euphrates, surrounded by a circular landmass showing Assyria, Urartu and several cities, in turn surrounded by a "bitter river" (Oceanus), with seven islands arranged around it so as to form a seven-pointed star. The accompanying text mentions seven outer regions beyond the encircling ocean. The descriptions of five of them have survived. In contrast to the Imago Mundi, an earlier Babylonian world map dating back to the 9th century BC depicted Babylon as being further north from the center of the world, though it is not certain what that center was supposed to represent.

The ideas of Anaximander (c. 610 BC-c. 545 BC), considered by later Greek writers to be the true founder of geography, come to us through fragments quoted by his successors. Anaximander is credited with the invention of the gnomon,the simple yet efficient Greek instrument that allowed the early measurement of latitude. Thales, Anaximander is also credited with the prediction of eclipses. The foundations of geography can be traced to the ancient cultures, such as the ancient, medieval, and early modern Chinese. The Greeks, who were the first to explore geography as both art and science, achieved this through Cartography, Philosophy, and Literature, or through Mathematics. There is some debate about who was the first person to assert that the Earth is spherical in shape, with the credit going either to Parmenides or Pythagoras. Anaxagoras was able to demonstrate that the profile of the Earth was circular by explaining eclipses. However, he still believed that the Earth was a flat disk, as did many of his contemporaries. One of the first estimates of the radius of the Earth was made by Eratosthenes.

The first rigorous system of latitude and longitude lines is credited to Hipparchus. He employed a sexagesimal system that was derived from Babylonian mathematics. The parallels and meridians were sub-divided into 360°, with each degree further subdivided 60′ (minutes). To measure the longitude at different location on Earth, he suggested using eclipses to determine the relative difference in time. The extensive mapping by the Romans as they explored new lands would later provide a high level of information for Ptolemy to construct detailed atlases. He extended the work of Hipparchus, using a grid system on his maps and adopting a length of 56.5 miles for a degree.

From the 3rd century onwards, Chinese methods of geographical study and writing of geographical literature became much more complex than what was found in Europe at the time (until the 13th century). Chinese geographers such as Liu An, Pei Xiu, Jia Dan, Shen Kuo, Fan Chengda, Zhou Daguan, and Xu Xiake wrote important treatises, yet by the 17th century, advanced ideas and methods of Western-style geography were adopted in China.

During the Middle Ages, the fall of the Roman empire led to a shift in the evolution of geography from Europe to the Islamic world. Muslim geographers such as Muhammad al-Idrisi produced detailed world maps (such as Tabula Rogeriana), while other geographers such as Yaqut al-Hamawi, Abu Rayhan Biruni, Ibn Battuta and Ibn Khaldun provided detailed accounts of their journeys and the geography of the regions they visited. Turkish geographer, Mahmud al-Kashgari drew a world map on a linguistic basis, and later so did Piri Reis (Piri Reis map). Further, Islamic scholars translated and interpreted the earlier works of the Romans and Greeks and established the House of Wisdom in Baghdad for this purpose. Abū Zayd al-Balkhī, originally from Balkh, founded the "Balkhī school" of terrestrial mapping in Baghdad. Suhrāb, a late tenth century Muslim geographer, accompanied a book of geographical coordinates with instructions for making a rectangular world map, with equirectangular projection or cylindrical equidistant projection.

Abu Rayhan Biruni (976-1048) first described a polar equi-azimuthal equidistant projection of the celestial sphere. He was regarded as the most skilled when it came to mapping cities and measuring the distances between them, which he did for many cities in the Middle East and Indian subcontinent. He often combined astronomical readings and mathematical equations, in order to develop methods of pin-pointing locations by recording degrees of latitude and longitude. He also developed similar techniques when it came to measuring the heights of mountains, depths of valleys, and expanse of the horizon. He also discussed human geography and the planetary habitability of the Earth. He also calculated the latitude of Kath, Khwarezm, using the maximum altitude of the Sun, and solved a complex geodesic equation in order to accurately compute the Earth's circumference, which were close to modern values of the Earth's circumference. His estimate of 6,339.9 km for the Earth radius was only 16.8 km less than the modern value of 6,356.7 km. In contrast to his predecessors who measured the Earth's circumference by sighting the Sun simultaneously from two different locations, al-Biruni developed a new method of using trigonometric calculations based on the angle between a plain and mountain top which yielded more accurate measurements of the Earth's circumference and made it possible for it to be measured by a single person from a single location.

The European Age of Discovery during the 16th and 17th centuries, where many new lands were discovered and accounts by European explorers such as Christopher Columbus, Marco Polo and James Cook, revived a desire for both accurate geographic detail, and more solid theoretical foundations in Europe. The problem facing both explorers and geographers was finding the latitude and longitude of a geographic location. The problem of latitude was solved long ago but that of longitude remained; agreeing on what zero meridian should be was only part of the problem. It was left to John Harrison to solve it by inventing the chronometer H-4, in 1760, and later in 1884 for the International Meridian Conference to adopt by convention the Greenwich meridian as zero meridian.

The 18th and 19th centuries were the times when geography became recognized as a discrete academic discipline and became part of a typical university curriculum in Europe (especially Paris and Berlin). The development of many geographic societies also occurred during the 19th century with the foundations of the Société de Géographie in 1821, the Royal Geographical Society in 1830, Russian Geographical Society in 1845, American Geographical Society in 1851, and the National Geographic Society in 1888. The influence of Immanuel Kant, Alexander von Humboldt, Carl Ritter and Paul Vidal de la Blache can be seen as a major turning point in geography from a philosophy to an academic subject.

Over the past two centuries the advancements in technology such as computers, have led to the development of geomatics and new practices such as participant observation and geostatistics being incorporated into geography's portfolio of tools. In the West during the 20th century, the discipline of geography went through four major phases: environmental determinism, regional geography, the quantitative revolution, and critical geography. The strong interdisciplinary links between geography and the sciences of geology and botany, as well as economics, sociology and demographics have also grown greatly especially as a result of Earth System Science that seeks to understand the world in a holistic view.

Notable geographers

• Eratosthenes (276BC - 194BC) - calculated the size of the Earth.
• Ptolemy (c.90–c.168) - compiled Greek and Roman knowledge into the book Geographia.
• Al Idrisi (Arabic: أبو عبد الله محمد الإدريسي‎; Latin: Dreses) (1100–1165/66) - author of Nuzhatul Mushtaq.
• Gerardus Mercator (1512–1594) - innovative cartographer produced the mercator projection
• Alexander von Humboldt (1769–1859) - Considered Father of modern geography, published the Kosmos and founder of the sub-field biogeography.
• Carl Ritter (1779–1859) - Considered Father of modern geography. Occupied the first chair of geography at Berlin University.
• Arnold Henry Guyot (1807–1884) - noted the structure of glaciers and advanced understanding in glacier motion, especially in fast ice flow.
• William Morris Davis (1850–1934) - father of American geography and developer of the cycle of erosion.
• Paul Vidal de la Blache (1845–1918) - founder of the French school of geopolitics and wrote the principles of human geography.
• Sir Halford John Mackinder (1861–1947) - Co-founder of the LSE, Geographical Association
• Carl O. Sauer (1889–1975) - Prominent cultural geographer
• Walter Christaller (1893–1969) - human geographer and inventor of Central place theory.
• Yi-Fu Tuan (1930-) - Chinese-American scholar credited with starting Humanistic Geography as a discipline.
• David Harvey (1935-) - Marxist geographer and author of theories on spatial and urban geography, winner of the Vautrin Lud Prize.
• Edward Soja (born 1941) - Noted for his work on regional development, planning and governance along with coining the terms Synekism and Postmetropolis.
• Michael Frank Goodchild (1944-) - prominent GIS scholar and winner of the RGS founder's medal in 2003.
• Doreen Massey (1944-) - Key scholar in the space and places of globalization and its pluralities, winner of the Vautrin Lud Prize.
• Nigel Thrift (1949-) - originator of non-representational theory.
• Ellen Churchill Semple (1863–1932) - She was America's first influential female geographer.

Institutions and societies

• Anton Melik Geographical Institute (Slovenia)
• National Geographic Society (U.S.)
• American Geographical Society (U.S.)
• National Geographic Bee (U.S.)
• Royal Canadian Geographical Society (Canada)
• Royal Geographical Society (UK)

Publications

• African Geographical Review
• Geographical Review

See also

Template:Misplaced Pages-Books

• Association of American Geographers
• Canadian Association of Geographers
• Gazetteer
• Geographer
• Geographical renaming
• Geography and places reference tables
• International Geographical Union
• Landform
• List of explorers
• List of geographers
• List of Russian explorers
• Map
• Navigator
• Philosophy of geography
• World map

Notes and references

1. "Online Etymology Dictionary". Etymonline.com. Retrieved 2009-04-17.
2. "Geography". The American Heritage Dictionary/ of the English Language, Fourth Edition. Houghton Mifflin Company. Retrieved October 9, 2006.
3. Pattison, W.D. (1990). "The Four Traditions of Geography" (PDF). Journal of Geography. 89 (5): 202–6. doi:10.1080/00221349008979196. ISSN 0022-1341. Reprint of a 1964 article.
4. Bonnett, Alastair What is Geography? London, Sage, 2008
5. http://web.clas.ufl.edu/users/morgans/lecture_2.prn.pdf
6. "1(b). Elements of Geography". Physicalgeography.net. Retrieved 2009-04-17.
7. ^ Hayes-Bohanan, James. "What is Environmental Geography, Anyway?". Retrieved October 9, 2006.
8. Hughes, William. (1863). The Study of Geography. Lecture delivered at King's College, London by Sir Marc Alexander. Quoted in Baker, J.N.L (1963). The History of Geography. Oxford: Basil Blackwell. p. 66. ISBN 0853280223.
9. "What is geography?". AAG Career Guide: Jobs in Geography and related Geographical Sciences. Association of American Geographers. Archived from the original on October 6, 2006. Retrieved October 9, 2006.
10. ^ Kurt A. Raaflaub & Richard J. A. Talbert (2009). Geography and Ethnography: Perceptions of the World in Pre-Modern Societies. John Wiley & Sons. p. 147. ISBN 1405191465.
11. Siebold, Jim Slide 103 via henry-davis.com - accessed 2008-02-04
12. http://www.jstor.org/pss/1151277 IMAGO MVNDI, Vol.48 pp.209
13. Finel, Irving (1995). A join to the map of the world: A notable discover. pp. 26–27.
14. Jean-Louis and Monique Tassoul (1920). A Concise History of Solar and Stellar Physics. London: Princeton University Press. ISBN 069111711X.
15. "Hipparcos of Rhodes". Technology Museum of Thessaloniki. 2001. Retrieved 2006-10-16.
16. Sullivan, Dan (2000). "Mapmaking and its History". Rutgers University. Retrieved 2006-10-16.
17. ^ Needham, Joseph (1986). Science and Civilization in China: Volume 3. Taipei: Caves Books, Ltd. Page 512.
18. "Education". IslamiCity.com. Retrieved 2009-04-17.
19. ^ E. Edson and Emilie Savage-Smith, Medieval Views of the Cosmos, pp. 61-3, Bodleian Library, University of Oxford
20. David A. King (1996), "Astronomy and Islamic society: Qibla, gnomics and timekeeping", in Roshdi Rashed, ed., Encyclopedia of the History of Arabic Science, Vol. 1, p. 128-184 . Routledge, London and New York.
21. James S. Aber (2003). Alberuni calculated the Earth's circumference at a small town of Pind Dadan Khan, District Jhelum, Punjab, Pakistan.Abu Rayhan al-Biruni, Emporia State University.
22. Lenn Evan Goodman (1992), Avicenna, p. 31, Routledge, ISBN 041501929X.
23. Aughton, Peter (2007). Voyages that changed the world. Quercus. p. 164. ISBN 1847240040. {{cite book}}: Check |isbn= value: checksum (help)
24. "Société de Géographie, Paris, France" (in French). Retrieved 2007-01-15.
25. "About Us". Royal Geographical Society. Retrieved 2007-01-15.
26. "Русское Географическое Общество (основано в 1845 г.)". Rgo.org.ru. Retrieved 2009-04-17.
27. "The American Geographical Society". Amergeog.org. 2009-04-02. Retrieved 2009-04-17.
28. "Inspiring People to Care About the Planet". National Geographic. 2002-10-17. Retrieved 2009-04-17.

External links

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