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- MEASURING ECONOMIC GROWTH FROM OUTER SPACE
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The legacy was then bestowed upon Vishnu Hari Dalmia. Yahoo India Celebrity Celebrities and their kids: their hand-in-hand pictures will brighten your day From Aarav and Twinkle, Nysa and Kajol to Tahira Kashyap and her babies, we spotted these celebrity parents out and about with their children this week.
Dalmia Group, an Indian conglomerate. Dalmia Group chairman Sanjay Dalmia was also seen. The Middle Class in Colonial India provides a good summary of the historiographical field, as well as extracts from both primary and secondary sources on the subject. C does not survive after filing of the challan. Estates spread across 39, hectares producing the world's finest tea. But, once again, the farmer did not know what was to happen. Then around B. It also traded in peanut candy, mustard oil and crash helmets. I have two sons and one daughter; P.
When Masaba Gupta was signed on as fashion director at Satya Paul, talk of her shifting base to Delhi was doing the rounds. Sanjay Dalmia, Successful Indian businessman. He understands complex technologies and is able to creatively present them in a simple and engaging manner. The second son of Indira or Mrs. Here you can access the FlashCards form Paper. Mumbai Rohit was heading Semac consultants Dalmia group and was known for his commitment, insight and delivering results. Delhi-based industrialist Sanjay Dalmia is in talks with Indiabulls Financial Services to amicably resolve the dispute over his alleged attempt to dupe the Mumbai-based firm to the tune of few hundred crores by mortgaging bogus property documents.
Housed under the Dalmia Group, the company encourages the use of Ayurvedic therapies for combating various health disorders and ailments. We are governmental Registered authorized financial helper. In one sentence: Much ado about nothing. Soon after their marriage, Indira and Feroze were arrested and detained for several months. The cases rejected more than two years back shall also be considered in such meeting. As a manager, he always surprised me on he handled situations. South Africa's President Jacob Zuma has been accused of having a corrupt relationship with members of the Indian-born Gupta family, and even letting them interfere in ministerial appointments Among many other hobbies and interests, Ramadorai is passionate about Indian classical music and photography.
Files are available under licenses specified on their description page. Sanjay Dalmia, Chairman of the Dalmia Group of Companies, is a pioneer who had the vision and courage to get away from the beaten track and create instit Sanjay Dalmia, Delhi, India. Based on the idea of depicting the history and culture of seven cities, veteran actor and film director Sanjay Khan has been given the green signal by the Uttar Pradesh government to set up a theme park in Agra.
Indira and Feroze were married according to Hindu rites. He grew close to the Nehru family, especially to Indira's mother Kamala Nehru, accompanying her to the TB Sanatorium at Bhowali in , helping arrange her trip to Europe when her condition worsened in April , and visiting her at the sanitarium at Badenweiler and Dinesh Dalmia: Rs crore. Our goal is to be the best tea producer in the world. It would be also better to look how the intellectual world and media evaluate Modi. M of for quashment of the order dated 5. Leave review Sanjay Dalmia. B Sinha, J. Hari Shankar Singhania.
But it takes more than the rich and diverse proffering of traditional Indian fare to maintain this position: These chefs, over years of work India, Mumbai, 12 February He was the husband of Indira Gandhi and the son-in-law to Jawaharlal Nehru. Over the years, the Dalmia Group has established itself as a dynamic and globally progressive conglomerate. A person travels 12 km due North, then 15 km due East, after that 15 km due West and then 15 km due South.
Kasiviswanathan has 2 jobs listed on their profile. They have one son and a daughter. He gained control over Dalmia Bros Pvt Ltd. Feroze first proposed to Indira in , but she and her mother rejected it, putting forward that she was too young, only About Essel Group. Daljit, son of Delhi-based real estate tycoon Mohinderjit Singh, builder of massive constructions like the Nike Town in Boston and Indira Gandhi Indoor Stadium in Delhi, then decided partying the night before his audition seemed like a good idea.
Facebook gives people the power to share and makes the Heckman is married to Lynne Pettler-Heckman, a sociologist. Ramalinga Raju, that he had embezzled funds to the tune of Rs. The doctor is married to the lawyer. It has a single unit located at Dalmiapuram in Tamil Nadu, with a capacity of 3. In his long, diverse and successful career spanning over four decades, Mr. But Sanjay Agarwal's finance portal was just a veil to cover up his shady deals.
More Sanjay Dutt Photos. Sanjay Dalmia, chairman of Dalmia group of companies. Nayar joined KKR in Contact Informati Dalmia, Indiabulls eye out-of-court settlement 7 Nov, , They were all successful in their own business domain but failed badly because media was not their primary Dinesh Dalmia was the managing director of DSQ Software Limited when the Central Bureau of Investigation arrested him for his involvement in a stocks scam of Rs crore Rs 5.
At present, it is managed by his sons Sanjay Dalmia and Anurag Dalmia. Civil from B. Royal Oldham Hospital 4 out of 5. One particularly memorable exchange between them never fades with repetition. While some have praised the dance sequence performed by Deepika Padukone. Checked that PS3Prox runs without giving you any errors 4.
Plugged the network cable into your PC and PS3 6. Make a note of this number, its always four numbers, in this case its This is normal 2. At this stage you can either download the file using your browser by clicking on the link 3. JPG B. Getting The Link Yourself If you don't find the link you are looking for in the Download list, all you have to do is start the download on your PS3 while connected to the Proxy and then cancel or pause it Returning to the Proxy you will find a new link to a PKG file This is the download link for the game you just tried to get, now you can use your preffered method to download the PKG file.
Don't forget to post the link in this thread so that it can be added to the download list for everyone else. Chances are someone has already downloaded the file you need and will be kind enough to post the link in the thread. Then all you have to do is use your preferred method of downloading the file Browser or Download Manager. Last edited by creemyv; December 2nd, at AM. Replacing the Download Link with the local PKG file There are actually three places where you can use the Proxy to replace a download link, the method you use is up to you but I would strongly suggest using number three as it will be used for the remainder of the guide 1.
An added bonus is that you can use this method to download files even if the PSN Store is down or undergoing maintenance.
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I prefer this method because it feels the easiest for me. This method is generally quicker but obviously requires more effort adding multiple IP links - Finally you can use the excellent script RogueRabbit created to populate the list with all the possible IP links Fastest method but please read through this post before using the script - The method I personally use is try to predict the IP for example the first IP I got was Then I Pause and Resume the download until it chose one of those three links.
It this case it did so after four times. Checked that PS3Prox runs without giving you any errors. Credits gamer for the original software and thread which was a great help to me and many other people using the Proxy. StefanDB for the original thread detailing how to use your PC to download Games, Demo's and Patches Seth for this post which was very helpful to me when I was still using " Ps3 proxy by CF3B5 " Kronik for this post which was the most up to date guide I could find in the original thread JinKira for the PSN URL List which he maintains, it should be your first port of call when looking for download links RogueRabbit for this post which explained the variable IP changes that were made after Firmware 4.
To enable me or any one else to help you troubleshoot your problems with the PS3 Proxy Server please make sure your post contains the following: - Your Operating System - Version of PS3 Proxy Server - Type of Internet Connection and Detailed settings of the Internet Connection - Game or Patch you are trying to install - Screengrab of any error messages If you want to say Thanks, please use the Thanks button, I want to keep this thread as Slim as possible so any unnecessary posts will be deleted. Last edited by creemyv; November 14th, at PM.
You Sir You are awsome!! Hidden Content. Ahh damn, i thought this was for a new version of the software! Thanks for this. I hope it'll be a sticky. Among the most widely investigated rapid climate events of the early to middle Holocene are two that took place about 8, and 4,, years ago. The former event Figures 2. Stager and Mayewski, If the mechanism for this event has been identified correctly, the event was a final deglacial, or.
High-resolution pollen studies show substantial and rapid vegetation response to the event in central Europe, with early biological changes lagging climate by less than 20 years Tinner and Lotter, Because so many Holocene climate records are available and the cause of the event is rather clear, it provides an opportunity for an especially well-documented test case of model sensitivity. The event is also important because it punctuated a time when temperatures were similar to or even slightly above more recent levels, demonstrating that warmth is no guarantee of climate stability.
A less well-understood hydrologic event from wet to dry conditions, occurring roughly 5, years ago, also took place during a warm period. This event is not as well documented and suffers from less than ideal temporal resolution of available records. Four mechanisms have been proposed to explain the event, all of which could have contributed. First, it might have been associated with a cooling in the North Atlantic, perhaps related to a slow-down in thermohaline circulation Street-Perrott and Perrott, ; Gasse and van Campo, ; Kutzbach and Liu, ; deMenocal et al.
Second, it might be related to a subtle and variable ca. Increasing attention is also being focused on the possibility that the ENSO system has changed its pattern of variability, perhaps rapidly. The best-documented shift in the frequency of ENSO variability occurred in Trenberth, , and it was probably one of several shifts in frequency to occur over the.
Discussion continues on the statistical significance and long-term persistence of these switches and on whether they should be considered evidence of normal oscillations, of short-lived abrupt shifts, or of long-lived abrupt climate change e.
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Further back in the Holocene, the ENSO system might have been dramatically different from today, with much reduced variability and fewer strong events Overpeck and Webb, ; Diaz and Markgraf, ; Cole, ; Sandweiss et al. Although the time at which modern ENSO variability became established is not known, there have been several model-based efforts to explain the changes, all tied to the response of the coupled atmosphere-ocean system to small orbitally induced insolation changes Bush, ; Otto-Bliesner, ; Clement et al.
The shift to more-modern ENSO variability also might have been coincident with other earth-system changes 4,, years ago. Sandweiss et al. Rodbell et al. Although there are other hints of important abrupt climate changes in the Holocene record, most of them have not been studied to the degree needed to place them in a coherent context for example, examined at multiple sites.
MEASURING ECONOMIC GROWTH FROM OUTER SPACE
One important observation is that the landfall frequency of catastrophic hurricanes has changed rapidly during the Holocene. For example, the period about 1,, years ago was active on the Gulf Coast compared with the last 1, years and changes in North Atlantic climate could be the primary cause Liu and Fearn, ; Donnelly et al.
The period near 1, years ago was also possibly marked by a substantial change in hydrologic regimes in Central and North America Hodell et al. Climate variations within the last millennium are, in general, better resolved temporally and spatially than are variations earlier in the Holocene. This is due largely to the greater availability of annually dated records from historical documents, trees, corals, ice cores and sediments, but this availability is also due to greater emphasis on the last millenium by large paleoenvironmental science programs, such as PAst Global changES PAGES of the International Geosphere-Biosphere Programme IGBP.
The shift and later state of substantial global warming were unprecedented in the context of the last years and might be due to a combination of natural such as solar and volcanic and human-induced such as trace-gas forcing Overpeck et al. In contrast with the abrupt late nineteenth to early twentieth century warming, timing of the onset of the Little Ice Age is difficult to establish in that the change manifests itself as a period of slow Northern Hemisphere cooling beginning at or before ca Mann et al.
There are insufficient paleoclimate records to allow complete reconstruction of the last 1, years of change in the Southern Hemisphere, and uncertainty remains on the amplitude of Northern Hemisphere change in this interval e. Moreover, evidence is scarce outside the North Atlantic-European sector Jennings and Weiner, ; Keigwin, ; Broecker, for medieval temperatures that were close to mean twentieth century levels.
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Additional annually resolved records for the last 2, years are needed to answer such fundamental questions. The existing temperature records, as described above, make it clear that natural variability alone can generate regional to hemispheric temperature anomalies that are sufficient to affect many aspects of human activity. However, the record of hydrologic change over the last 2, years suggests even larger effects: there is ample evidence that decadal, even century-scale, drought can occur with little or no warning.
A synthesis of US drought variability over the last 2, years Woodhouse and Overpeck, used records from a diverse array of proxy sources cf. Cronin et al. From this synthesis, it was concluded that multi-year droughts similar to the s Dust. Bowl or the severe s southwest drought have occurred an average of once or twice per century over the last 2, years.
The last of these occurred in the sixteenth century, spanned much of northern Mexico to Canada, and lasted over 20 years in some regions Woodhouse and Overpeck, ; Stahle et al. An earlier event in the thirteenth century also persisted for decades in some locations and involved the long-term drying of lakes in the Sierra Nevada of California Stine, and the activation of desert dunes in parts of the High Plains Muhs and Holliday, , There is evidence of even longer droughts further back than the last millennium Stine, ; Laird et al.
An important conclusion from paleodrought research is that drought regimes can shift rapidly and without warning. A prominent example is the shift, at about BP, from a regime characterized by frequent long droughts on the High Plains to the current regime of less-frequent and shorter droughts Laird et al. Despite growing knowledge of the paleodrought record, causal mechanisms of changes are poorly understood Woodhouse and Overpeck, There is also good evidence of late Holocene multidecadal droughts outside North America e.
Thus, although we know that droughts unprecedented in the last years have occurred in the last 2, years and so could occur in the future, we do not have the scientific understanding to predict them or recognize their onset. Just as the twentieth century instrumental record is too short to understand the full range of drought, it is too short to understand how the fre-. Data on past hydrological conditions from the upper Mississippi River Knox, and from sediments in the Gulf of Mexico Brown et al.
In the western United States, there is growing evidence that flood regimes distinctly different from today, and also episodic in time, were the norm rather than the exception. The frequency of large floods in the Lower Colorado River Basin, for example, appears to have varied widely over the last 5, years Ely et al. Those flood-frequency fluctuations and substantial fluctuations elsewhere around the world e.
Clearly, a predictive understanding of megadroughts and large floods must await further research. This observation about droughts and floods applies at some level to all the abrupt climate changes recorded in proxy records. The data are clear. Ice-age events were especially large and widespread and involved changes in temperature, precipitation, windiness, and so on. Holocene events were more muted in polar regions, might have been more regionalized, and usually involved water availability, but often with important temperature changes as well.
Multi-characteristic global-anomaly maps are not available for any of the abrupt changes, and additional records and proxy techniques will be required to provide such anomaly maps. Coverage gaps appear especially large in the oceans and southern latitudes, although broad gaps also exist elsewhere. Instrumental records from scientific monitoring programs offer the possibility of capturing directly the relevant data on abrupt climate change with greater accuracy and spatial coverage than are possible from the necessarily limited proxy records.
The relatively short period of instrumental records means that they have missed most of the abrupt changes discussed above, although some droughts and the warming from the Little Ice Age have been captured rather well. Instrumental records will become more valuable as their length increases, which argues for maintenance of key.
Instrumental records also are critical in characterizing patterns of climate variability that might have contributed to paleoclimatic abrupt change, and might contribute to abrupt climate change in the future. The abrupt changes surveyed here are smaller in strength than the extreme events of the paleoclimate record, yet they are nonetheless significant as human populations press the capacity of the environment, locally and globally. Atmospheric instrumental data include surface values and vertical profiles of numerous physical variables, including temperature, pressure, radiation, and winds.
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Surface observations, satellite radiometric observations, and the global network of regularly launched radiosonde profilers are assimilated into computer models of the atmosphere to analyze weather and climate. They capture both the conditions that cause atmospheric circulation and the resulting atmospheric motions. Much of our current understanding of climate comes from the relatively accurately observed period since More subtle are the measurements of trace chemicals, which both affect the physical state of the atmosphere, and can be used to infer its motions.
The longest atmospheric time series, dating back several hundred years, are surface temperature and pressure. The ocean, like the atmosphere, is a thin fluid envelope covering much of the earth. Satellites are now collecting global observations of the temperature, elevation and roughness of the sea surface, which tell us the surface currents and winds fairly accurately.
Crucial climate variables, such as sea-ice cover and movement and to a lesser accuracy, ice thickness , have been measured by satellites beginning in the s. Yet, oceanic data are still more restricted in coverage and duration than atmospheric data, for it is still difficult to penetrate the depths of the ocean with instruments in sufficient numbers. In addition to the purely instrumental problem, ocean currents and eddies are smaller in size than major atmospheric wind fields, making the mapping of ocean circulation more difficult weather patterns are well matched in size to the spacing of major cities, which historically made their discovery possible, using simple barometers.
Another contrasting property is the time for fluid to adjust fully to a change in external forcing: in the atmosphere this time is a month or two, while in the ocean it is measured in millennia. The ocean dominates the global storage of heat, carbon, and.
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Thus, it is fortunate that temperature records are among the longest oceanic time-series and have the best spatial coverage. Data sets include sea-surface temperatures from ocean vessels, long coastal sea-level and temperature records, and shorter or more scattered time-series of temperature and salinity from surface to sea-floor. Increasingly long time-series of directly measured ocean currents are becoming available, particularly in the tropics.
Over longer times other aspects of oceanic circulation, chemistry and biology become important to climate. For example, the heat storage available to the atmosphere is strongly dependent on circulation and salinity stratification of the upper ocean. The depths of the ocean become involved as the thermohaline circulation THC and wind-driven circulation interact to reset surface conditions. Direct measurements of the circulation of the deep ocean are still sparse, and indirect means are often used to infer the circulation. Water density from measured temperature and salinity can be combined with dynamical constraints and atmospheric observations of air-sea interaction to estimate global ocean circulation e.
The results are consistent with the limited direct measurements of currents, and also with the patterns of observed chemical tracers in the ocean. The tracers include natural dissolved gases and nutrients, dynamical quantities such as potential vorticity and potential density, and chemical inputs from human activity. Transient chemical tracers, injected into the atmosphere and subsequently absorbed by the ocean, provide particularly useful images of the ocean circulation. Bomb radiocarbon, tritium and chlorofluorocarbons CFCs , for example, allow verification and quantitative assessment of the pathways of high-latitude sinking, equatorward flow in boundary currents, and interaction with the slower flow of mid-ocean regions Broecker and Peng, ; Doney and Jenkins, ; Smethie and Fine, The location, strength and depth penetration of the major sinking regions of the ocean at high latitude see Plate 4 are known to have changed during glacial cycles, emphasizing the importance of sea-ice cover in insulating the ocean from the atmosphere, preventing deep convection and physical sinking from occurring e.
The contrasting effect of freezing sea-water is that salty brine is rejected from the ice, yielding a small but very dense volume of water that can contribute to sinking events. During the twentieth century lesser yet still significant shifts of the deep circulation e. Abrupt changes in climate can occur with spatial patterns that in some way reflect the natural dynamics of atmosphere and ocean.
Natural variability of climate is now occurring in the context of global warming, so the discussion of abrupt climate change during the period of instrumental records must acknowledge the presence of anthropogenic and natural change, and the possibility of strong interaction between them. Instrumental records show that the climate is characterized by patterns or modes of variability, such as the polar annular modes and ENSO of the equatorial Pacific, as described below. The spatial patterns can provide regional intensification of climate change in quite small geographic areas.
The strong couplings and feedbacks among at least the atmosphere, oceans and sea ice, and probably other elements of the climate system, allow a pattern to persist for periods of years to many decades.
The different regional modes also interact with one another. For instance, Amazonian rainfall responds to a mode of tropical Atlantic variability, which itself might be responding to ENSO or the Arctic Oscillation. Hansen and Sutera , Corti et al. However observational evidence has been questioned e. Also, questions remain about whether such behavior should be characteristic of an entity with as many degrees of freedom as the climate system Dymnikov and Gritsoun, The possibility that mode shifts participated in or provide clues to the large, abrupt climate changes of preinstrumental times suggests common mechanisms or even common causes.
Thus, the study of abrupt climate change should involve consideration of the preferred modes of the climate system. The annular modes—the Arctic Oscillation AO and the Antarctic Oscillation AAO —primarily affect polar to middle-latitude regions in both the North and South and are the dominant modes of climate variability in these areas, especially in the winter. The AO and AAO represent a transfer of atmospheric mass between subtropical high-pressure regions and polar lows.
A strongly positive state of an annular mode is associated with intensified highs and lows driving strong atmospheric circulation. The negative state has much less difference between high- and low-pressure regions and thus is related to weaker atmospheric circulation. The southern annular mode is moderately symmetric about the pole, but owing to the complex geometry of northern continents, the AO is especially strong over the North Atlantic and less evident in other regions. When the winter pressure difference is large, frequent strong storms take a northeasterly track across the North Atlantic, producing warm and wet weather in northern Europe, cold and dry conditions in northern Canada, and mild and wet conditions along the US East Coast.
In contrast, a small pressure difference produces fewer, weaker storms, taking an easterly track to produce a moist Mediterranean, cold northern Europe, and a snowy US East Coast in response to frequent cold-air outbursts. The coupled oscillation of the tropical ocean and atmosphere is important in global climate, with impacts that extend far beyond the tropical Pacific to the tropical Atlantic and Indian Oceans, to the Southern Ocean, and to middle to high latitudes in the Northern Hemisphere. ENSO might be linked to another of the leading patterns of variability, the so-called Pacific North American PNA pattern, which exerts a strong influence on distribution of rainfall and surface temperature over western North America.
Like the AO, the PNA pattern fluctuates randomly from one month to the next, but also exhibits what appear to be systematic variations on a much longer time scale. Since , the positive polarity of the PNA pattern—marked by a tendency toward relatively mild winters over Alaska and western Canada, below-normal rainfall and stream flows over the Pacific Northwest, and above-normal rainfall in the southwestern United States—has been prevalent, whereas during the preceding year period the opposite conditions prevailed.
The abrupt shift toward the positive polarity of the PNA pattern in was coincident with and believed to be caused by a widespread pattern of changes throughout the Pacific Ocean. Sea-surface temperatures along the equatorial belt and along the coast of the Americas became warmer, while farther to the west at temperate latitudes the sea surface became cooler Nitta and Yamada, ; Trenberth, ; Graham, An array of changes in the marine ecosystem occurred around the same time Ebbesmeier et al. For example, salmon recruitment underwent a major readjustment toward more abundant harvests along the Alaskan coast accompanied by deteriorating conditions in southern British Columbia and the US Pacific Northwest Francis and Hare, The suite of atmospheric and oceanic changes that have been linked to these basin-wide regime shifts is collectively referred to as the Pacific Decadal Oscillation PDO Mantua et al.
An unusually large fraction of disturbances moves northeastward, bringing mild, wet weather to the Alaska panhandle; many of the remainder track southeastward, bringing heavy rains to southern California and the US desert Southwest. The mountain ranges of British Columbia and the US Pacific Northwest, which lie directly downstream from the split in the storm track, tend to receive less than the normal amount of winter snowfall, and this reduces water supplies for the following summer season. Hence, regime shifts such as the one that occurred in are difficult to diagnose in real time, let alone to predict.
There are several different schools of thought as to the nature of the interdecadal PDO variability, which has shown both the abruptness and persistence to qualify under our definition of abrupt climate change. The default hypothesis is that the PDO is merely a reflection of stochastic variability originating in the atmosphere but amplified by positive feedbacks associated with coupling between the atmosphere and ocean Bretherton and Battisti, If this interpretation is valid, it follows that this ENSO-like variability is inherently unpredictable i.
Hopes that the phenomenon is deterministic, and therefore predictable, are based on the notion that ocean dynamics play an active role in PDO evolution, to the extent of setting the time scale for the major swings back and forth between the positive and negative polarity of the PDO pattern. One oceanic process that could conceivably set the time scale is the recirculation time for water parcels in the clockwise North Pacific and counterclockwise South Pacific subtropical.
A second subtropical gyre time scale is set by the time it takes for oceanic planetary waves to propagate to the western boundary currents, which then feed back on the atmospheric circulation. Mechanisms that depend on those processes have been demonstrated to be capable of producing ENSO-like interdecadal variability in coupled atmosphere-ocean models Latif and Barnett, Species and shell chemistry and isotopic ratios of planktonic foraminfera Lee et al. Stronger glacial easterly equatorial winds are inferred Lyle, Tropical variability arising from feedbacks within the Atlantic and Indian equatorial regions also contributes to regional climate modes, although of smaller global impact than ENSO, probably because of the vast width of the Pacific relative to the Atlantic or Indian.
Off-equatorial modes of tropical Atlantic variability are associated with the strength and location of the northern and southern Intertropical Convergence Zones ITCZs ; work in recent years has revealed that Northern and Southern Hemisphere SST variability are not tightly linked. Tropical Atlantic variability has a major impact on rainfall in northern Africa and northern South America and an impact on hurricane frequency and patterns in the North Atlantic. In the Indian tropical region, the seasonal monsoon driven by ocean-land temperature contrasts has a major impact on human life.
The monsoon is perhaps the classic example of ocean-atmosphere-land interactions. During boreal summer, a northward shift of the ITCZ to the Indian sub-continent creates a major precipitation and heat source in this region. In contrast, drought and desertification, when they occur in extratropical latitudes, are primarily summer phenomena whose geographic distribution and evolution are determined as much by land-surface processes as by atmospheric dynamics. Dynamical modes may still be involved, however, as the summer pattern of great anticyclones over the oceans responds to the heating of the continents.
Kelvin and Rossby waves are active in determining the shape, extent, and flow of moisture in this pattern Rodwell and Hoskins, , and in turn these waves are involved in dynamical modes as noted above. An extended drought popularly known as the Dust Bowl affected large areas of the United States through most of the decade of the s. Much of the topsoil was irreversibly lost—blown away in dust storms that darkened skies as far downstream as the eastern seaboard. Numerous farms were abandoned, and agricultural productivity dropped sharply.
Many who lived through the Dust Bowl must have wondered whether climatic conditions would ever be suitable for farming again. Yet toward the end of the decade, the rains returned, and the region has never since been plagued by such an extended drought. What initiated the Dust Bowl in the early s and what caused the rains to return nearly a decade later are still open questions. The prevailing view is that drought is an inherently stochastic phenomenon, initiated and terminated by random fluctuations in atmospheric circulation patterns, and sustained over long periods of time by positive feedback from the terrestrial biosphere Namias, ; Rind, ; Shukla and Mintz, ; Karl, ; Sud and Molod, ; Bravar and Kavvas, ; Xue and Shukla, ; Dirmeyer, ; Lare and Nicholson, A few weeks of abnormally hot, dry weather are sufficient to desiccate the upper layers of the soil, reducing the water available for plants to absorb through their root systems.
The plants respond by reducing the rate of evapotranspiration through leaves during the daylight hours Dirmeyer, ; Radersma and de Reider, ; Xue et al. This favors higher afternoon temperatures and also reduces the humidity within the lower km of the atmosphere Walsh et al. Because this boundary-layer air is the source of roughly half the moisture that condenses in summer rainstorms over the central United States, lower humidity favors reduced precipitation Brubaker et al. Higher daily maximum temperatures, lower humidity, and reduced precipitation all increase the stress on plants.
If the stress is sufficiently severe and long, the physiological changes in plants become irreversible. Once the threshold is crossed, the earliest hope for the restoration of normal vegetation is the next spring growing season, which can be 6 or even 9 months away. Throughout the remainder of the summer and early autumn, the parched land surface continues to exert a feedback on the atmosphere that perpetuates the abnormally hot, dry weather conditions Yeh et al.
The wilting of the plants also affects hydrological conditions in the ground. In the absence of healthy root systems, water runs off more rapidly after rainstorms, leaving behind less to nurture the plants. Once the water table drops substantially, an extended period of near- or above-normal precipitation is required to restore groundwater Palmer, ; Entekhabi et al. The remarkable year-to-year persistence of the s drought attests to the memory of the.
Once established, an arid climate regime, such as the one that prevailed during the Dust Bowl, appears to be capable of perpetuating itself until a well-timed series of rainstorms enables the vegetation to regain a foothold Dirmeyer and Shukla, ; Wang and Eltahir, a,b; Clark et al. The onset and termination of the s Dust Bowl are examples of abrupt regime shifts from a climate conducive to agriculture to a climate more characteristic of a desert region and back again.
During the time covered by instrumental records, such shifts have occurred rather infrequently in the United States but more regularly in semiarid agricultural regions, such as the Sahel, northeast Brazil, and the Middle East Nicholson et al. Thus far, the United States has experienced relatively little true desertification, but other regions of the globe have not been as fortunate. For example, it is well documented that the Sahara expanded northward and engulfed formerly productive agricultural regions of North Africa during the last few centuries of the Roman Empire Reale and Dirmeyer, ; this transition might well have involved a series of prolonged drought episodes analogous to the Dust Bowl.
Agricultural practices influence the retention of topsoil. Poor cultivation practices and overgrazing have been blamed for the desertification that has plagued North Africa, the Sahel, and other semi-arid regions Otterman ; Wendler and Eaton, ; Balling, ; Bryant et al. Whether adherence to environmentally sound agricultural practices will be sufficient to prevent further desertification is less clear.
Global warming could render such regions as the western and central United States more vulnerable to extended drought episodes by increasing temperatures during the growing season, and thereby increasing the rate of evapotranspiration. There is no conclusive evidence of such behavior in response to the rapid warming of the last two decades, but simulations with climate models indicate that more pronounced warming like that predicted to occur by the end of the twenty-first century could serve to increase the frequency of drought episodes and the risk of irreversible desertification Rind et al.
Instrumental records are becoming long enough to show trends in climate, although the distinction between trends and longer cycles is never simple. The Little Ice Age set the stage for the global warming of the last century, which probably had both natural and anthropogenic causes Intergovernmental Panel on Climate Change, b. A brief review of some of the main trends is provided here, showing that these trends often exhibit regional abruptness and are linked to modes of climate variability, again documenting the importance of instrumental records to the study of abrupt climate change.
Most long instrumental records were initiated in the nineteenth and twentieth centuries. The central England temperature time series is one of the longest continuous instrumental climate records Figure 2. Top figure shows summer and bottom figure shows winter. Temperature scale is in degrees Celcius. Data courtesy of P. Jones, University of East Anglia. Long cool periods, such as the summers throughout the nineteenth century, were punctuated by extreme events.
The cold phases were known to have had important effects on human activity, as in the abrupt European cooling from the unusually warm s to the cold s. Famine occurred across western Europe, especially in Ireland and France, where farmers who depended on wheat and potatoes were slow to adapt. Snow fell in July in northern New England, farming was disrupted, and crops failed.
The event might have spurred the westward migration of farmers from the thin soils of the hill farms of New Hampshire. There was severe drought in Brazil in Single volcanic eruptions often have a widespread cooling effect e.
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Volcanic forcing also represents an experiment in which the response of global climate modes can be observed in great detail, helping understand how modes might respond to other forcings. The winter atmospheric circulation in the Northern Hemisphere has undergone some remarkable changes during the last several decades. Sea-level pressures over the Arctic have fallen by about 6 hPa Walsh et al. Related circulation changes have favored mild winters over most of Russia, China and Japan, and drought over southern Europe and parts of the Middle East Hurrell, ; Thompson et al.
Warming during the period has been concentrated in central and northern Asia and northwestern North America. Retreating glaciers, warming permafrost, and decreasing sea-ice cover have been observed in Alaska, where temperatures increased abruptly in the late s, distinct from the post acceleration of globally averaged temperature rise. The patterns in these. There are indications of analogous trends in the Southern Hemisphere, in association with its annular mode Thompson et al.
Several ideas have been put forth concerning the cause of those trends. Shindell et al. Indeed, similar trends have been simulated in an atmospheric model driven by increasing concentrations of greenhouse gases. It has also been suggested that stratospheric ozone depletion Volodin and Galin, and trends in sea-surface temperatures Rodwell et al. Because favored patterns of variability tend to be highly sensitive to external forcing, it is indeed quite plausible that they can be changed in a number of ways.
Fyfe et al. The trend has altered the distribution of deep convection over the North Atlantic Lilly et al. For example, the recovery of the stratospheric ozone layer from human-induced depletion during the twentieth century could be delayed by several decades Shindell et al. Global-average surface temperature records show two principal periods of warming during the twentieth century. The warming following has occurred widely, yet with regions of concentration in northern Asia and northwestern North America.
Anthropogenic forcing is widely suspected to be a contributing cause Intergovernmental Panel on Climate Change, b. The warming earlier in the century is less likely to be of anthropogenic origin, although this is an unsettled issue; solar and volcanic forcing may have played a role Delworth and Knutson, ; Stott et al. Global temperature has evolved very differently, in space, during the two warmings Figure 2.
The earlier twentieth-century episode was concentrated in the far north. The warming seems to have appeared first in the Barents Sea; for example, in the records from Turuhansk, a city on the Yenisey River in northern Siberia. Sparse temperature records are supplemented by observations of a strong increase in ocean salinity and decrease in sea ice cover in the Nordic Seas Kelley et al.
Land stations only Delworth and Knutson, Reading figure from left to right, one sees the rapid, concentrated arrival of warm temperatures in the s, contrasting the late twentieth century warming that is spread across many latitudes. Temperature scale is in degrees Celsius. Effects of those sudden changes on oceanic ecosystems were widespread Intergovernmental Panel on Climate Change, a, Ch. Northward dislocations of plankton, fish, mammals, and birds were extreme, including the range of economically important species, such as herring Figure 2.
In the case of cod, the warm ocean greatly extended their range, as larvae were transported north by the Irminger Current from the waters around Iceland. The northern catch rose from nothing to , tons per year in the s and s, then declined abruptly when the surface cold water reappeared in the late s. Earlier successful cod fisheries were seen near Greenland in the s and s, but none had occurred in the wide interval between then and Such effects were also widespread in the Nordic and Barents Seas.
Causes of the abrupt yet long-lasting northern warming are not clear. The Arctic region as a whole seems to amplify climate variability, as we are witnessing now. Climate-model simulations Delworth and Mann, suggested that the warming could have occurred with strong natural variability, through an increase in oceanic meridional overturning circulation, which brought warm, saline surface waters into the sub-Arctic and Arctic.
In that. Durre, personal communication, SSB bold line ; temperature thin line. The close proximity of the northern Atlantic focus of this warming to the dominant sinking regions of the global deep-ocean circulation makes this episode particularly relevant to global climate. Long-term measurements appropriate to climate variability studies are scarce in the ocean.
Temperature records at a few coastal sites, and tide gauge records, have been sustained. Around , a network of ocean weather stations was established by the International Civil Aviation Organization, mostly for atmospheric measurements. In the United States, these were manned by ships of the U. Coast Guard. A few, however—such as Bravo in the Labrador Sea, Mike in the Norwegian Sea, and Papa in the subpolar North Pacific—carried out deep hydrographic stations, as well as weather observations. The value of those time series is enormous.
Fortunately, for climate purposes, we do not always need rapidly sampled data. In the northwestern Atlantic the annual range of seasonal. Sampling must be frequent enough so as not to be aliased by this cycle.