Misplaced Pages

#374625

84-470: The warm period was followed by a gradual decline, of about 0.1 to 0.3 °C per millennium, until about two centuries ago. However, on a sub-millennial scale, there were regional warm periods superimposed on this decline. The HCO was approximately 4.9 °C warmer than the Last Glacial Maximum . A study in 2020 estimated that the average global temperature during the warmest 200 year period of

168-520: A cold reversal caused a replacement of much of the arboreal vegetation with Magellanic moorland and Alpine species. On Isla Grande de Chiloé , Magellanic moorland and closed-canopy Nothofagus forests were both present during the LGM, but the former disappeared by the late LGM. Little is known about the extent of glaciers during Last Glacial Maximum north of the Chilean Lake District . To

252-730: A formal measurement of uncalibrated radiocarbon years , counted from 1950). In New Zealand and neighbouring regions of the Pacific, temperatures may have been further depressed during part of the LGM by the world's most recent supervolcanic eruption , the Oruanui eruption , approximately 25,500 years BP. However, it is estimated that during the LGM, low-to-mid latitude land surfaces at low elevation cooled on average by 5.8 °C relative to their present-day temperatures, based on an analysis of noble gases dissolved in groundwater rather than examinations of species abundances that have been used in

336-612: A full glacial cycle from the Holocene into the previous Eemian interglacial. The Renland ice core is 325 m long. Although the depths are different, the GRIP and NGRIP cores also contain the climatic optimum at very similar times. The climatic event was probably a result of predictable changes in the Earth's orbit ( Milankovitch cycles ) and a continuation of changes that caused the end of the last glacial period . The effect would have had

420-658: A hot and wet climate in India along with high sea levels. Relative sea level in the Spermonde Archipelago was approximately 0.5 metres higher than it is today. Sedimentary infill of lagoons was retarded by the sea level highstand and accelerated after the HCO, when sea levels dropped. West African sediments additionally record the African humid period , an interval between 16,000 and 6,000 years ago during which Africa

504-488: A local glacial maximum in the region. In northeastern Italy , in the region around Lake Fimon , Artemisia -dominated semideserts, steppes, and meadow-steppes replaced open boreal forests at the start of the LGM, specifically during Heinrich Stadial 3. The overall climate of the region became both drier and colder. In the Sar Mountains , the glacial equilibrium-line altitude was about 450 metres lower than in

588-410: A mixture of grassland and tundra prevailed, and even here, the northern limit of tree growth was at least 20° farther south than today. In the period before the LGM, many areas that became completely barren desert were wetter than they are today, notably in southern Australia, where Aboriginal occupation is believed to coincide with a wet period between 40,000 and 60,000 years Before Present (BP,

672-694: A result of rising sea levels and decay of ice sheets in the Northern Hemisphere, the East Asian Summer Monsoon (EASM) rain belt expanded to the northwest, penetrating deep into the Asian interior. The EASM, being significantly weaker before and after the HCO, peaked in strength during this interval, though the exact timing of its maximum intensity varied by region; intensified westerlies occasionally caused dry spells in China during

756-461: A slow change in vegetation towards a sparsely distributed vegetation dominated by Nothofagus species. Within this parkland vegetation Magellanic moorland alternated with Nothofagus forest, and as warming progressed even warm-climate trees began to grow in the area. It is estimated that the tree line was depressed about 1,000 m relative to present day elevations during the coldest period, but it rose gradually until 19,300 years ago. At that time

840-718: A warmer and wetter overall climate in the region. The stability of the Middle Holocene climate in China fostered the development of agriculture and animal husbandry in the region. In the Korean Peninsula, arboreal pollen records the HCO as occurring from 8,900 to 4,400 BP, with its core period being 7,600 to 4,800 BP. Sea levels in the Sea of Japan were 2-6 metres higher than in the present, with sea surface temperatures being 1-2 °C higher. The East Korea Warm Current reached as far as Primorye and pushed cold water off of

924-632: Is approximately at 3,200 metres (10,500 ft). Sedimentary sandstone rocks found near the Tibetan capital of Lhasa contain grains of magnetic minerals that record the Earth's alternating magnetic field current. The basin of the Yarlung River, bounded by the Himalayas in the south and Kang Rinpoche and Nyenchen Tanglha Mountains in the north, has less severe climate than the adjacent northern (and higher-altitude) parts of Tibet, and

SECTION 10

#1732765343375

1008-547: Is home to most of the population of the Tibetan Autonomous Region . The Yarlung Tsangpo Grand Canyon , formed by a horse-shoe bend in the river where it leaves the Tibetan Plateau and flows around Namcha Barwa , is the deepest, and possibly longest canyon in the world. The Yarlung Tsangpo River has three major waterfalls in its course. The largest waterfall of the river, the "Hidden Falls",

1092-615: Is located in the Tibet Autonomous Region , China . It is the longest river of Tibet and the fifth longest in China. The upper section is also called Dangque Zangbu meaning "Horse River." Originating at Angsi Glacier in western Tibet, southeast of Mount Kailash and Lake Manasarovar , it later forms the South Tibet Valley and Yarlung Tsangpo Grand Canyon before passing into the state of Arunachal Pradesh , India . Downstream from Arunachal Pradesh,

1176-637: Is referred to in Britain as the Dimlington Stadial , dated to between 31,000 and 16,000 years ago. The average global temperature about 21,000 years ago was about 6 °C (11 °F) colder than today. According to the United States Geological Survey (USGS), permanent summer ice covered about 8% of Earth's surface and 25% of the land area during the last glacial maximum. The USGS also states that sea level

1260-675: The Baltic Shield , and in Russia in particular, the LGM ice margin of the Fennoscandian Ice Sheet was highly lobate. The main LGM lobes of Russia followed the Dvina , Vologda and Rybinsk basins respectively. Lobes originated as result of ice following shallow topographic depressions filled with a soft sediment substrate. The northern Ural region was covered in periglacial steppes. Permafrost covered Europe south of

1344-780: The Barents Sea , the Kara Sea , and Novaya Zemlya , ending at the Taymyr Peninsula in what is now northwestern Siberia. Warming commenced in northern latitudes around 20,000 years ago, but it was limited and considerable warming did not take place until around 14,600 year ago. In northwestern Russia , the Fennoscandian ice sheet reached its LGM extent approximately 17,000 years ago, about five thousand years later than in Denmark, Germany and Western Poland. Outside

1428-614: The Cantabrian Mountains of the northwestern corner of the Iberian Peninsula , which in the present day have no permanent glaciers, the LGM led to a local glacial recession as a result of increased aridity caused by the growth of other ice sheets farther to the east and north, which drastically limited annual snowfall over the mountains of northwestern Spain. The Cantabrian alpine glaciers had previously expanded between approximately 60,000 and 40,000 years ago during

1512-644: The Ganges , which in Bangladesh is called the Padma . When leaving the Tibetan Plateau , the river forms the world's largest and deepest canyon, Yarlung Tsangpo Grand Canyon . The Yarlung Tsangpo River is the highest major river in the world. Its longest tributary is the Nyang River . Major tributaries of Yarlung Tsangpo include Nyangchu River, Lhasa River , Nyang River , and Parlung Tsangpo . In Tibet

1596-772: The Gulf of Oman . Bathymetric data suggests there were two palaeo-basins in the Persian Gulf. The central basin may have approached an area of 20,000 km , comparable at its fullest extent to lakes such as Lake Malawi in Africa. Between 12,000 and 9,000 years ago much of the Gulf's floor was not covered by water, only being flooded by the sea after 8,000 years ago. It is estimated that annual average temperatures in Southern Africa were 6 °C lower than at present during

1680-617: The Hex River Mountains , in the Western Cape , block streams and terraces found near the summit of Matroosberg evidences past periglacial activity which likely occurred during the LGM. Palaeoclimatological proxies indicate the region around Boomplaas Cave was wetter, with increased winter precipitation. The region of the Zambezi River catchment was colder relative to present and the local drop in mean temperature

1764-676: The Last Glacial Coldest Period , was the most recent time during the Last Glacial Period where ice sheets were at their greatest extent 26,000 and 20,000 years ago. Ice sheets covered much of Northern North America , Northern Europe , and Asia and profoundly affected Earth 's climate by causing a major expansion of deserts, along with a large drop in sea levels. Based on changes in position of ice sheet margins dated via terrestrial cosmogenic nuclides and radiocarbon dating , growth of ice sheets in

SECTION 20

#1732765343375

1848-645: The Strait of Magellan suggest the peak in glacial surface area was constrained to between 25,200 and 23,100 years ago. There are no agreed dates for the beginning and end of the LGM, and researchers select dates depending on their criteria and the data set consulted. Jennifer French, an archeologist specialising in the European Palaeolithic, dates its onset at 27,500 years ago, with ice sheets at their maximum by around 26,000 years ago and deglaciation commencing between 20,000 and 19,000 years ago. The LGM

1932-641: The savannas that make up the coastal lowlands of the Congo River drainage basin in the present were entirely absent. Southwestern Africa experienced increased humidity during the HCO. Northwestern Patagonia , in a region known as the Arid Diagonal , was significantly drier during the Early and Middle Holocene , with the region becoming more humid during the Late Holocene following the end of

2016-606: The Andes occupying lacustrine and marine basins where they spread out forming large piedmont glacier lobes . Glaciers extended about 7 km west of the modern Llanquihue Lake , but not more than 2 to 3 km south of it. Nahuel Huapi Lake in Argentina was also glaciated by the same time. Over most of the Chiloé Archipelago , glacier advance peaked 26,000 years ago, forming a long north–south moraine system along

2100-567: The Great Barrier Reef was enhanced due to low atmospheric CO 2 levels. The deep waters of the Indian Ocean were significantly less oxygenated during the LGM compared to the Middle Holocene. The deep South Indian Ocean in particular was an enormous carbon sink, partially explaining the very low p CO 2 of the LGM. The intermediate waters of the southeastern Arabian Sea were poorly ventilated relative to today because of

2184-608: The HCO (post-glacial climatic optimum) probably occurred at the same time. A similar comparison is evident between the Dye 3 1979 and the Camp Century 1963 cores regarding this period. The Hans Tausen Ice Cap , in Peary Land (northern Greenland ), was drilled in 1977, with a new deep drill to 325 m. The ice core contained distinct melt layers all the way to the bedrock. That indicates that Hans Tausen Iskappe contains no ice from

2268-691: The HCO in the southern Ural Mountains was simultaneous with that in Northern Europe , while its termination occurred between 6,300 and 5,100 BP. Winter warming of 3 to 9 °C and summer warming of 2 to 6 °C occurred in northern central Siberia . The HCO was highly asynchronous in Central and East Asia, though it at least occurred contemporaneously in the Loess Plateau, the Inner Mongolian Plateau, and Xinjiang. As

2352-659: The HCO, around 6,500 years ago, was around 0.7 °C warmer than the mean for nineteenth century AD, immediately before the Industrial Revolution , and 0.3 °C cooler than the average for 2011-2019. The 2021 IPCC report expressed medium confidence that temperatures in the last decade are higher than they were in the Mid-Holocene Warm Period. Temperatures in the Northern Hemisphere are simulated to be warmer than present average during

2436-534: The HCO. In the far Southern Hemisphere (New Zealand and Antarctica), the warmest period during the Holocene appears to have been roughly 10,500 to 8,000 years ago, immediately after the end of the last ice age . The Amery Ice Shelf retreated approximately 80 kilometres landward during this warm interval. By 6,000 years ago, which is normally associated with the Holocene Climatic Optimum in

2520-653: The HCO. Current desert regions of Central Asia were extensively forested because of higher rainfall, and the warm temperate forest belts in China and Japan were extended northwards. In the Yarlung Tsangpo valley of southern Tibet, precipitation was up to twice as high as it is today during the middle Holocene. In the Huai River basin, the HCO began 9,100 to 8,000 BP. Pollen records from Lake Tai in Jiangsu , China shed light on increased summer precipitation and

2604-547: The Holocene. In Greece , steppe vegetation predominated. Megafaunal abundance in Europe peaked around 27,000 and 21,000 BP; this bountifulness was attributable to the cold stadial climate. In Greenland, the difference between LGM temperatures and present temperatures was twice as great during winter as during summer. Greenhouse gas and insolation forcings dominated temperature changes in northern Greenland, whereas Atlantic meridional overturning circulation (AMOC) variability

Holocene climatic optimum - Misplaced Pages Continue

2688-678: The LGM except in transient intervals around 23,200 and 22,300 BP. In the western South Atlantic , where Antarctic Intermediate Water forms, sinking particle flux was heightened as a result of increased dust flux during the LGM and sustained export productivity. The increased sinking particle flux removed neodymium from shallow waters, producing an isotopic ratio change. On the Island of Hawaii , geologists have long recognized deposits formed by glaciers on Mauna Kea during recent ice ages. The latest work indicates that deposits of three glacial episodes since 150,000 to 200,000 years ago are preserved on

2772-544: The LGM, 21,000 years ago, the sea level was about 125 meters (about 410 feet) lower than it is today. Across most of the globe, the hydrological cycle slowed down, explaining increased aridity in many regions of the world. In Africa and the Middle East, many smaller mountain glaciers formed, and the Sahara and other sandy deserts were greatly expanded in extent. The Atlantic deep sea sediment core V22-196, extracted off

2856-702: The Last Glacial Maximum. This temperature drop alone would however not have been enough to generate widespread glaciation or permafrost in the Drakensberg Mountains or the Lesotho Highlands . Seasonal freezing of the ground in the Lesotho Highlands might have reached depths of 2 meters or more below the surface. A few small glaciers did however develop during the LGM, in particular in south-facing slopes. In

2940-688: The Laurentide Ice Sheet reached 3.2 km in height around Keewatin Dome and about 1.7-2.1 km along the Plains divide. In addition to the large Cordilleran Ice Sheet in Canada and Montana , alpine glaciers advanced and (in some locations) ice caps covered much of the Rocky and Sierra Nevada Mountains further south. Latitudinal gradients were so sharp that permafrost did not reach far south of

3024-705: The North Atlantic was reduced, as measured by the increased proportion of radiogenic isotopes in neodymium isotope ratios. There is controversy whether upwelling off the Moroccan coast was stronger during the LGM compared to today. Though coccolith size increases in Calcidiscus leptoporus suggest stronger trade winds during the LGM caused there to be increased coastal upwelling of the northwestern coast of Africa, planktonic foraminiferal δ C records show upwelling and primary productivity were not enhanced during

3108-465: The North Atlantic were better ventilated during the LGM by Glacial North Atlantic Intermediate Water (GNAIW) relative to its present-day ventilation by upper North Atlantic Deep Water (NADW). GNAIW was nutrient poor compared to present day upper NADW. Below GNAIW, southern source bottom water that was very rich in nutrients filled the deep North Atlantic. Due to the presence of immense ice sheets in Europe and North America, continental weathering flux into

3192-476: The Northern Hemisphere, those regions had reached temperatures similar to today, and they did not participate in the temperature changes of the north. However, some authors have used the term "Holocene Climatic Optimum" to describe the earlier southern warm period as well; typically, the term "Early Holocene Climatic Optimum" is used for the Southern Hemisphere warm interval. In New Zealand, the HCO

3276-416: The atmosphere . The massive sheets of ice locked away water, lowering the sea level, exposing continental shelves , joining land masses together, and creating extensive coastal plains . The ice sheets also changed the atmospheric circulation, causing the northern Pacific and Atlantic oceans to cool and produce more clouds, which amplified the global cooling as the clouds reflected even more sunlight. During

3360-919: The best known being Lake Bonneville in Utah . This also occurred in Afghanistan and Iran , where a major lake formed in the Dasht-e Kavir . In Australia , shifting sand dunes covered half the continent, while the Chaco and Pampas in South America became similarly dry. Present-day subtropical regions also lost most of their forest cover, notably in eastern Australia, the Atlantic Forest of Brazil , and southern China , where open woodland became dominant due to much drier conditions. In northern China – unglaciated despite its cold climate –

3444-402: The coast of Senegal, shows a major southward expansion of the Sahara. The Persian Gulf averages about 35 metres in depth and the seabed between Abu Dhabi and Qatar is even shallower, being mostly less than 15 metres deep. For thousands of years the Ur-Shatt (a confluence of the Tigris - Euphrates Rivers ) provided fresh water to the Gulf, as it flowed through the Strait of Hormuz into

Holocene climatic optimum - Misplaced Pages Continue

3528-420: The continents: the Indonesian islands as far east as Borneo and Bali were connected to the Asian continent in a landmass called Sundaland . Palawan was also part of Sundaland, while the rest of the Philippine Islands formed one large island separated from the continent only by the Sibutu Passage and the Mindoro Strait . The environment along the coast of South China was not very different from that of

3612-405: The cooler Primorsky Current to the northeast. The Tsushima Current warmed the northern shores of Hokkaido penetrated into the Sea of Okhotsk . In the northern South China Sea , the HCO was associated with colder winters due to a stronger East Asian Winter Monsoon (EAWM), causing frequent coral die-offs. In the Indian Subcontinent , the Indian Summer Monsoon (ISM) heavily intensified, creating

3696-466: The east and west extremities of the Sundaland shelf. Only in Central America and the Chocó region of Colombia did tropical rainforests remain substantially intact – probably due to the extraordinarily heavy rainfall of these regions. Most of the world's deserts expanded. Exceptions were in what is the present-day Western United States , where changes in the jet stream brought heavy rain to areas that are now desert and large pluvial lakes formed,

3780-491: The eastern coast of Chiloé Island (41.5–43° S). By that time the glaciation at the latitude of Chiloé was of ice sheet type contrasting to the valley glaciation found further north in Chile. Despite glacier advances much of the area west of Llanquihue Lake was still ice-free during the Last Glacial Maximum. During the coldest period of the Last Glacial Maximum vegetation at this location was dominated by Alpine herbs in wide open surfaces. The global warming that followed caused

3864-614: The global band of thunderstorms, the Intertropical Convergence Zone . However, orbital forcing would predict maximum climate response several thousand years earlier than those observed in the Northern Hemisphere. The delay may be a result of the continuing changes in climate, as the Earth emerged from the last glacial period and related to ice–albedo feedback . Different sites often show climate changes at somewhat different times and lasting for different durations. At some locations, climate changes may have begun as early as 11,000 years ago or have persisted until 4,000 years ago. As noted above,

3948-423: The gorge from 1973 on, had already taken pictures of the falls in 1987 from a helicopter. Since the 1990s the Yarlung Tsangpo River has been the destination of a number of teams that engage in exploration and whitewater kayaking . The river has been called the "Everest of Rivers" because of the extreme conditions of the river. The first attempt to run was made in 1993 by a Japanese group who lost one member on

4032-581: The ice sheet down to as far south as present-day Szeged in Southern Hungary. Ice covered the whole of Iceland . In addition, ice covered Ireland along with roughly the northern half of the British Isles with the southern boundary of the ice sheet running approximately from the south of Wales to the north east of England, and then across the now submerged land of Doggerland to Denmark . Central Europe had isolated pockets of relative warmth corresponding to hydrothermally active areas, which served as refugia for taxa not adapted to extremely cold climates. In

4116-421: The ice sheets except at high elevations. Glaciers forced the early human populations who had originally migrated from northeast Siberia into refugia , reshaping their genetic variation by mutation and drift . This phenomenon established the older haplogroups found among Native Americans , and later migrations are responsible for northern North American haplogroups. In southeastern North America, between

4200-456: The last glaciation and so the world's northernmost ice cap melted away during the post-glacial climatic optimum and was rebuilt when the climate cooled some 4000 years ago. From the delta-profile, the Renland ice cap in the Scoresby Sound has always been separated from the inland ice, but all of the delta-leaps revealed in the Camp Century 1963 core recurred in the Renland 1985 ice core. The Renland ice core from East Greenland apparently covers

4284-420: The maximum heating of the Northern Hemisphere 9,000 years ago, when the axial tilt was 24° and the nearest approach to the Sun ( perihelion ) was during the Northern Hemisphere's summer. The calculated Milankovitch Forcing would have provided 0.2% more solar radiation (+40 W/m) to the Northern Hemisphere in summer, which tended to cause more heating. There seems to have been the predicted southward shift in

SECTION 50

#1732765343375

4368-412: The north, in the dry Andes of Central and the Last Glacial Maximum is associated with increased humidity and the verified advance of at least some mountain glaciers. Montane glaciers in the northern Andes reached their peak extent approximately 27,000 years ago. In northwestern Argentina, pollen deposits record the altitudinal descent of the treeline during the LGM. Amazonia was much drier than in

4452-601: The optimum than now. Northwestern North America reached peak warmth first, from 11,000 to 9,000 years ago, but the Laurentide Ice Sheet still chilled eastern Canada. Northeastern North America experienced peak warming 4,000 years later. Along the Arctic Coastal Plain in Alaska, there are indications of summer temperatures 2–3 °C warmer than now. Research indicates that the Arctic had less sea ice than now. The Greenland Ice Sheet thinned, particularly at its margins. In addition to being warmer, Arctic Alaska also became wetter. Northwestern Europe experienced warming, but there

4536-428: The past. During the Last Glacial Maximum, much of the world was cold, dry, and inhospitable, with frequent storms and a dust-laden atmosphere. The dustiness of the atmosphere is a prominent feature in ice cores; dust levels were as much as 20 to 25 times greater than they are in the present. This was probably due to a number of factors: reduced vegetation, stronger global winds, and less precipitation to clear dust from

4620-654: The persistence of rainforests in eastern Australia at this time. Rivers maintained their sinuous form in southeastern Australia and there was increased aeolian deposition of sediment in compared to today. The Flinders Ranges likewise experienced humid conditions. In southwestern Western Australia, forests disappeared during the LGM. Between Sahul and Sundaland – a peninsula of South East Asia that comprised present-day Malaysia and western and northern Indonesia – there remained an archipelago of islands known as Wallacea . The water gaps between these islands, Sahul and Sundaland were considerably narrower and fewer in number than in

4704-413: The portion from 7,500 to 6,300 BP with human impact only observed in pollen records, and the portion after 6,300 BP with substantial human influence on the environment. In the Middle East , the HCO was associated with frost-free winters and abundant Pistacia savannas . It was during this interval that the domestication of cereals and Neolithic population growth occurred in the region. The onset of

4788-744: The present day, featuring moist subtropical evergreen forests, despite sea levels in the South China Sea being about 100 metres lower than the present day. The Australian mainland, New Guinea , Tasmania and many smaller islands comprised a single land mass. This continent is now referred to sometimes as Sahul . In the Bonaparte Gulf of northwestern Australia, sea levels were about 125 metres lower than present. Interior Australia saw widespread aridity, evidenced by extensive dune activity and falling lake levels. Eastern Australia experienced two nadirs in temperature. Lacustrine sediments from North Stradbroke Island in coastal Queensland indicated humid conditions. Data from Little Llangothlin Lagoon likewise indicate

4872-507: The present day. The two main islands of New Zealand, along with associated smaller islands, were joined as one landmass. Virtually all of the Southern Alps were under permanent ice cover, with alpine glaciers extending from them into much of the surrounding high country . Northern Europe was largely covered by ice, with the southern boundary of the ice sheets passing through Germany and Poland. This ice extended northward to cover Svalbard and Franz Josef Land and northeastward to occupy

4956-498: The present, with flora diminished to almost the same degree as in glaciated areas of Europe and North America. Even in less affected regions, rainforest cover was greatly diminished, especially in West Africa where a few refugia were surrounded by tropical grasslands . The Amazon rainforest was split into two large blocks by extensive savanna , and the tropical rainforests of Southeast Asia probably were similarly affected, with deciduous forests expanding in their place except on

5040-485: The present. δ D values from plant waxes from the LGM are significantly more enriched than those in the present and those dating back to MIS 3, evidencing this increased aridity. Eastern Brazil was also affected; the site of Guanambi in Bahia was much drier than today. AMOC was weaker and more shallow during the LGM. Sea surface temperatures in the western subtropical gyre of the North Atlantic were around 5 °C colder compared to today. Intermediate depth waters of

5124-430: The river becomes far wider and is called the Siang. After reaching Assam , the river is known as the Brahmaputra . From Assam, the river enters Bangladesh at Ramnabazar. From there until about 200 years ago it used to flow eastward and joined the Meghna River near Bhairab Upazila . This old channel has been gradually dying. At present the main channel of the river is called Jamuna River , which flows southward to meet

SECTION 60

#1732765343375

5208-448: The river flows through the South Tibet Valley, which is approximately 1,200 kilometres (750 mi) long and 300 kilometres (190 mi) wide. The valley descends from 4,500 metres (14,800 ft) above sea level to 3,000 metres (9,800 ft). As it descends, the surrounding vegetation changes from cold desert to arid steppe to deciduous scrub vegetation. It ultimately changes into conifer and rhododendron forest. The tree line

5292-459: The river. In October 1998, a kayaking expedition sponsored by the National Geographic Society attempted to navigate the Yarlung Tsangpo Grand Canyon . Troubled by unanticipated high water levels, the expedition ended in tragedy with the death of expert kayaker Doug Gordon . In January–February 2002, an international group consisting of Scott Lindgren, Steve Fisher, Mike Abbott, Allan Ellard, Dustin Knapp, and Johnnie and Willie Kern, completed

5376-407: The shutting down of the Oyashio Current and the presence of large east–west mountain ranges were secondary factors that prevented the development of continental glaciation in Asia . All over the world, climates at the Last Glacial Maximum were cooler and almost everywhere drier. In extreme cases, such as South Australia and the Sahel , rainfall could have been diminished by up to 90% compared to

5460-400: The southern Appalachian Mountains and the Atlantic Ocean, there was an enclave of unusually warm climate. In the Southern Hemisphere, the Patagonian Ice Sheet covered the whole southern third of Chile and adjacent areas of Argentina. On the western side of the Andes the ice sheet reached sea level as far north as in the 41 degrees south at Chacao Channel . The western coast of Patagonia

5544-437: The southern hemisphere commenced 33,000 years ago and maximum coverage has been estimated to have occurred sometime between 26,500 years ago and 20,000 years ago. After this, deglaciation caused an abrupt rise in sea level. Decline of the West Antarctica ice sheet occurred between 14,000 and 15,000 years ago, consistent with evidence for another abrupt rise in the sea level about 14,500 years ago. Glacier fluctuations around

5628-413: The summers, but the tropics and parts of the Southern Hemisphere were colder than average. The average temperature change appears to have declined rapidly with latitude and so essentially no change in mean temperature is reported at low and middle latitudes. Tropical reefs tend to show temperature increases of less than 1 °C. The tropical ocean surface at the Great Barrier Reef about 5350 years ago

5712-440: The volcano. Glacial moraines on the volcano formed about 70,000 years ago and from about 40,000 to 13,000 years ago. If glacial deposits were formed on Mauna Loa , they have long since been buried by younger lava flows. Low sea surface temperature (SST) and sea surface salinity (SSS) in the East China Sea during the LGM suggests the Kuroshio Current was reduced in strength relative to the present. Abyssal Pacific overturning

5796-518: The warmest interval in the far south significantly preceded warming in the north. Significant temperature changes do not appear to have occurred at most low-latitude sites, but other climate changes have been reported, such as significantly wetter conditions in Africa, Australia and Japan and desert-like conditions in the Midwestern United States . Areas around the Amazon show temperature increases and drier conditions. Last Glacial Maximum The Last Glacial Maximum ( LGM ), also referred to as

5880-662: The weakened thermohaline circulation. Evidence from sediment cores in the Scotia Sea suggests the Antarctic Circumpolar Current was weaker during the LGM than during the Holocene. The Antarctic Polar Front (APF) was located much farther to the north compared to its present-day location. Studies suggest it could have been placed as far north as 43°S, reaching into the southern Indian Ocean. Yarlung Tsangpo The Yarlung Tsangpo , also called Yarlung Zangbo ( Tibetan : ཡར་ཀླུངས་གཙང་པོ་ , Wylie : yar kLungs gTsang po , ZYPY : Yarlung Zangbo ) and Yalu Zangbu River ( Chinese : 雅鲁藏布江 ; pinyin : Yǎlǔzàngbù Jiāng )

5964-410: The wet period occurred within decades, not the previously-thought extended periods. It is hypothesized that humans played a role in altering the vegetation structure of North Africa at some point after 8,000 years ago by introducing domesticated animals, which contributed to the rapid transition to the arid conditions that are now found in many locations in the Sahara . Further south, in Central Africa ,

6048-565: Was 1 °C warmer and enriched in O by 0.5 per mil relative to modern seawater. Temperatures during the HCO were higher than in the present by around 6 °C in Svalbard , near the North Pole. Of 140 sites across the western Arctic, there is clear evidence for conditions that were warmer than now at 120 sites. At 16 sites for which quantitative estimates have been obtained, local temperatures were on average 1.6±0.8 °C higher during

6132-629: Was a pocket of relative warmth. Following a preceding period of relative retreat from 52,000 to 40,000 years ago, the Laurentide Ice Sheet grew rapidly at the onset of the LGM until it covered essentially all of Canada east of the Rocky Mountains and extended roughly to the Missouri and Ohio Rivers , and eastward to Manhattan , reaching a total maximum volume of around 26.5 to 37 million cubic kilometres. At its peak,

6216-750: Was about 125 meters (410 ft) lower than in present times (2012). When comparing to the present, the average global temperature was 15 °C (59 °F) for the 2013–2017 period. As of 2012 about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice. Carbon sequestration in the highly stratified and productive Southern Ocean was essential in producing the LGM. The formation of an ice sheet or ice cap requires both prolonged cold and precipitation ( snow ). Hence, despite having temperatures similar to those of glaciated areas in North America and Europe , East Asia remained unglaciated except at higher elevations. This difference

6300-483: Was associated with a 2 °C temperature gradient across the subtropical front (STF), a sharp contrast with the 6 °C observed today. Westerly winds in New Zealand were reduced. A comparison of the delta profiles at Byrd Station , West Antarctica (2164 m ice core recovered, 1968), and Camp Century , Northwest Greenland, shows the post-glacial climatic optimum. Points of correlation indicate that in both locations,

6384-517: Was because the ice sheets in Europe produced extensive anticyclones above them. These anticyclones generated air masses that were so dry on reaching Siberia and Manchuria that precipitation sufficient for the formation of glaciers could never occur (except in Kamchatka where these westerly winds lifted moisture from the Sea of Japan ). The relative warmth of the Pacific Ocean due to

6468-535: Was cooling in Southern Europe . In the southwestern Iberian Peninsula , forest cover reached its peak between 9,760 and 7,360 years BP as a result of high moisture availability and warm temperatures during the HCO. In Central Europe , the HCO was when human impact on the environment first became clearly detectable in sedimentological records, with the portion of the HCO from 9,000 to 7,500 BP being associated with minimal human impact and environmental stability,

6552-486: Was largely glaciated, but some authors have pointed out the possible existence of ice-free refugia for some plant species. On the eastern side of the Andes, glacier lobes occupied the depressions of Seno Skyring , Seno Otway , Inútil Bay , and Beagle Channel . On the Straits of Magellan, ice reached as far as Segunda Angostura . During the LGM, valley glaciers in the southern Andes (38–43° S) merged and descended from

6636-509: Was much wetter than now. That was caused by a strengthening of the African monsoon by changes in summer radiation, which resulted from long-term variations in the Earth's orbit around the Sun . The " Green Sahara " was dotted with numerous lakes , containing typical African lake crocodile and hippopotamus fauna. A curious discovery from the marine sediments is that the transitions into and out of

6720-485: Was not publicized in the West until 1998, when its sighting by Westerners was briefly hailed as a "discovery." They were even portrayed as the discovery of the great falls which had been the topic of stories told to early westerners by Tibetan hunters and Buddhist monks , but which had never been found by Western explorers at the time. The Chinese authorities contradicted, however, saying that Chinese geographers, who explored

6804-729: Was seasonally uniform. On the island of Mauritius in the Mascarenhas Archipelago , open wet forest vegetation dominated, contrasting with the dominantly closed-stratified-tall-forest state of Holocene Mauritian forests. There were ice sheets in modern Tibet (although scientists continue to debate the extent to which the Tibetan Plateau was covered with ice) as well as in Baltistan and Ladakh . In Southeast Asia , many smaller mountain glaciers formed, and permafrost covered Asia as far south as Beijing . Because of lowered sea levels, many of today's islands were joined to

6888-570: Was similar in spatial extent. The outflow of North Pacific Intermediate Water through the Tasman Sea was stronger during the LGM. In the Great Barrier Reef along the coast of Queensland , reef development shifted seaward due to the precipitous drop in sea levels, reaching a maximum distance from the present coastline as sea levels approached their lowest levels around 20,700-20,500 years ago. Microbial carbonate deposition in

6972-505: Was the dominant influence on southern Greenland's climate. Illorsuit Island was exclusively covered by cold-based glaciers. Eastern Beringia was extremely cold and dry. July air temperatures in northern Alaska and Yukon were about 2-3 °C lower compared to today. Equilibrium line altitudes in Alaska suggest summer temperatures were 2-5 °C compared to preindustrial. Sediment core analysis from Lone Spruce Pond in southwestern Alaska show it

7056-526: Was weaker during the LGM than in the present day, although it was temporarily stronger during some intervals of ice sheet retreat. The El Niño–Southern Oscillation (ENSO) was strong during the LGM. Evidence suggests that the Peruvian Oxygen Minimum Zone in the eastern Pacific was weaker than it is in the present day, likely as a result of increased oxygen concentrations in seawater permitted by cooler ocean water temperatures, though it

#374625