Rising at the west end of Great Slave Lake in Canada's Northwest Territories, the Mackenzie River flows northwestward for almost 1100 miles to the Beaufort Sea. Un-dammed and winding through Subarctic and Arctic wilderness, its wide, braided channel is just the final conduit of a massive watershed that covers 20% of Canada, extending from northeast British Columbia, northern Alberta, northwest Saskatchewan and the western Yukon to the massive Mackenzie River Delta, the 12th largest on our planet. If one includes its most distant tributaries, this river system exceeds 2600 miles in length (the longest in Canada) and drains a watershed of almost 700,000 square miles.
To the southwest, the Peace and Athabaska Rivers rise on the east side of the Continental Divide in the northern Canadian Rockies; these large streams merge to form a large inland delta along Lake Athabaska, which drains to Great Slave Lake via the Slave River. Leaving Great Slave Lake, the Mackenzie River picks up meltwaters from the Mackenzie Mountains (to its west) via the Liard River system and then receives flow from Great Bear Lake, to its east, the largest lake in Canada. At its braided delta, just east of the Richardson Mountains, the Mackenzie discharges copious amounts of relatively warm, fresh, nutrient-rich water into the Arctic Ocean; this annual discharge, the 14th largest on Earth, dramatically affects the regional ecosystem, allowing boreal woodlands to extend well north of their usual range and increasing the diversity of plants and animals across the ever-changing delta. Beluga whales gather here in spring to molt in the mild river current and the countless, shallow lakes provide ideal breeding habitat for shorebirds, tundra swans and snow geese. Resident mammals include black bears, barren ground grizzlies, Arctic fox, Arctic wolves, caribou, moose, musk ox and a massive number of muskrats.
However, all is not well in this seemingly pristine wilderness. Dams on tributaries of the Mackenzie have reduced flow through its primary channel and are diminishing the annual floods that are crucial to the welfare of its delta ecosystem. In addition, worrisome levels of mercury have been found in the river over the past few years, the product of mining and power plant effluent across the watershed. Of course, as with other Arctic ecosystems, global warming may dramatically affect the natural diversity of this magnificent yet fragile landscape.
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Tampilkan postingan dengan label climate. Tampilkan semua postingan
Selasa, 08 Mei 2012
Kamis, 16 Februari 2012
Erosional Remnants
Mention erosional remnants and we tend to think of sea stacks, free-standing buttes and other solitary rock formations that have withstood the forces of wind, water and ice. Some of these landforms, especially mesas and buttes, are protected by a resistant cap of basalt or other non-porous rock while others are igneous plutons or laccoliths, uncovered as their encasing sediments have eroded away.
In reality, all natural landforms are erosional remnants, the current product of underlying geology, tectonic forces and erosion, modified by climate and vegetation. Highlands may represent areas of uplift, volcanism or resistant geologic strata but remain subject to the forces of erosion and, eventually, will wear down to a level plain. Stream valleys and canyons, while seemingly stable during our brief lifespan, are continually molded by floods, deposition, landslides, rock falls and periods of drought; depending upon the interaction of these factors, they may deepen, widen, clog with erosional debris or fill with water behind a natural dam of ice or soil.
Human activity hastens erosion in a number of ways. Deforestation augments erosion on hillsides, the drainage of wetlands increases flooding along river valleys and the construction of highways disrupts natural drainage, increases runoff and, in mountainous regions, hastens the occurrence of rock slides. As we witnessed during the Dust Bowl years, poor farming practices can dramatically augment soil erosion and the over-grazing of natural grasslands continues to threaten those regions. And, of course, our contribution to global warming will significantly affect erosional processes as glaciers retreat, sea levels rise and weather patterns change.
In reality, all natural landforms are erosional remnants, the current product of underlying geology, tectonic forces and erosion, modified by climate and vegetation. Highlands may represent areas of uplift, volcanism or resistant geologic strata but remain subject to the forces of erosion and, eventually, will wear down to a level plain. Stream valleys and canyons, while seemingly stable during our brief lifespan, are continually molded by floods, deposition, landslides, rock falls and periods of drought; depending upon the interaction of these factors, they may deepen, widen, clog with erosional debris or fill with water behind a natural dam of ice or soil.
Human activity hastens erosion in a number of ways. Deforestation augments erosion on hillsides, the drainage of wetlands increases flooding along river valleys and the construction of highways disrupts natural drainage, increases runoff and, in mountainous regions, hastens the occurrence of rock slides. As we witnessed during the Dust Bowl years, poor farming practices can dramatically augment soil erosion and the over-grazing of natural grasslands continues to threaten those regions. And, of course, our contribution to global warming will significantly affect erosional processes as glaciers retreat, sea levels rise and weather patterns change.
Jumat, 30 Desember 2011
An Extreme Weather Year
By all accounts, 2011 has been a year of extreme weather across the U.S. Severe flooding in New England, a catastrophic drought across the Southern Plains, the worst tornado outbreak in recorded history, massive haboobs in the West and destructive wildfires across Texas have all dominated the headlines.
While years like this spawn doomsday discussions about the viability of our ecosystems, the threat to agriculture and the future welfare of mankind, they have no true predictive value. Though a backdrop of global warming cannot be ignored, these outbreaks of severe weather are more directly related to stagnant weather patterns, atmospheric derangements that often produce adjacent extremes of heat and cold, deluge and drought etc. A warmer climate may add fuel to the fire but the events themselves are sporadic; the last comparable episode of tornadic activity was in 1974 (almost 40 years ago) and the disastrous hurricane season of 2005 has since been followed by rather tepid years for tropical storms in the Atlantic Basin.
Periods of extreme weather always grab our attention and, since we are still rebounding from a glacial epoch, they are likely to be more intense when they do occur. But our relatively brief history of recorded weather gives us the impression that these outbreaks are both more extreme and less common than they actually have been from the broader perspective of Earth's history. Rather, we are now here to observe, document and be threatened by natural events that molded this planet long before our species evolved (or had the capability to record them).
While years like this spawn doomsday discussions about the viability of our ecosystems, the threat to agriculture and the future welfare of mankind, they have no true predictive value. Though a backdrop of global warming cannot be ignored, these outbreaks of severe weather are more directly related to stagnant weather patterns, atmospheric derangements that often produce adjacent extremes of heat and cold, deluge and drought etc. A warmer climate may add fuel to the fire but the events themselves are sporadic; the last comparable episode of tornadic activity was in 1974 (almost 40 years ago) and the disastrous hurricane season of 2005 has since been followed by rather tepid years for tropical storms in the Atlantic Basin.
Periods of extreme weather always grab our attention and, since we are still rebounding from a glacial epoch, they are likely to be more intense when they do occur. But our relatively brief history of recorded weather gives us the impression that these outbreaks are both more extreme and less common than they actually have been from the broader perspective of Earth's history. Rather, we are now here to observe, document and be threatened by natural events that molded this planet long before our species evolved (or had the capability to record them).
Kamis, 22 Desember 2011
Ice Age Relics
Mention Ice Age relics and most of us think of frozen mammoth carcasses, unearthed Neandertal bones or that living relic, the musk ox. More sophisticated students of natural history might also picture various forms of glacial terrain, erratic boulders or relic groves of hemlock, surviving the warm Holocene in shaded valleys of the Temperate Zone.
In fact, most modern plants and animals lived during the Pleistocene, having "moved" to warmer latitudes or to deeper waters when glaciers advanced and sea levels fell. Of course, the colder and wetter climate of the Pleistocene also spawned the evolution of new species, such as polar bears and Arctic fox, as their ancestors adapted to changing conditions.
We humans are also children of the Pleistocene, having appeared about 130,000 years ago, late in the course of that 2 million year Epoch. Like other creatures, we adapted to its shifting climate but, due to our large brains, we did not require new physical traits to survive; rather, we used fire, clothing and shelter for protection from the cold and took advantage of Pleistocene land bridges or ice shelves to colonize the globe. Like the musk ox and the polar bear, we are living relics of the Ice Age.
In fact, most modern plants and animals lived during the Pleistocene, having "moved" to warmer latitudes or to deeper waters when glaciers advanced and sea levels fell. Of course, the colder and wetter climate of the Pleistocene also spawned the evolution of new species, such as polar bears and Arctic fox, as their ancestors adapted to changing conditions.
We humans are also children of the Pleistocene, having appeared about 130,000 years ago, late in the course of that 2 million year Epoch. Like other creatures, we adapted to its shifting climate but, due to our large brains, we did not require new physical traits to survive; rather, we used fire, clothing and shelter for protection from the cold and took advantage of Pleistocene land bridges or ice shelves to colonize the globe. Like the musk ox and the polar bear, we are living relics of the Ice Age.
Jumat, 02 Desember 2011
Evolution & Climate Change
Most life forms, including the first unicellular organisms, evolved in tropical ecosystems. Even today, the Tropics harbor the great majority of species on Earth and provide an environment in which new species are most likely to evolve.
Over the eons, adaptation to a temperate or cold climate fostered more diversity as plants and animals dispersed across the planet, continents drifted toward colder latitudes and Earth's climate gyrated between periods of glaciation and global warming. Physical traits such as feathers, fur and fat insulation favored survival in the cold while some species developed behavioral adaptations such as migration, estivation or hibernation to survive in regions with a dramatic change in seasonal conditions.
We humans also evolved in the Tropics but, thanks to our large brains, were able to adapt quickly to colder climates without "waiting" for natural selection to control our expansion; the capacity to utilize fire, produce clothing and construct shelters fueled our dispersal across the globe. Nevertheless, climate change and its associated natural forces continue to challenge our welfare and how we adapt to global warming will determine the future course of human history.
Over the eons, adaptation to a temperate or cold climate fostered more diversity as plants and animals dispersed across the planet, continents drifted toward colder latitudes and Earth's climate gyrated between periods of glaciation and global warming. Physical traits such as feathers, fur and fat insulation favored survival in the cold while some species developed behavioral adaptations such as migration, estivation or hibernation to survive in regions with a dramatic change in seasonal conditions.
We humans also evolved in the Tropics but, thanks to our large brains, were able to adapt quickly to colder climates without "waiting" for natural selection to control our expansion; the capacity to utilize fire, produce clothing and construct shelters fueled our dispersal across the globe. Nevertheless, climate change and its associated natural forces continue to challenge our welfare and how we adapt to global warming will determine the future course of human history.
Sabtu, 02 Juli 2011
Tropical Storm Dynamics
The development of a tropical storm is dependent upon three factors: warm ocean waters, hot, humid air at the surface and light upper-level winds. For these reasons, early season Atlantic hurricanes usually develop in the relatively shallow waters of the Gulf of Mexico, across the Caribbean and along the Southeast Coast of the U.S. While tropical waves begin to move westward, out of Africa, in early summer, they encounter cool waters in the central Atlantic and tropical storms do not usually develop; by August, the ocean temperature has increased and the peak of the Atlantic hurricane season begins, continuing through September and into early October.
Once a tropical storm develops, favorable conditions, discussed above, may cause it to strengthen into a hurricane. Conversely, if the storm moves into cooler waters, makes landfall or encounters strong upper level winds, the storm dynamics break down and the system weakens or dissipates. In some cases, favorable conditions may be re-encountered and the storm may redevelop; this occasionally occurs in Central America, when Gulf of Mexico storms weaken over land and then re-blossom in the eastern Pacific.
Global warming may extend the hurricane season by producing warm ocean waters earlier in the summer and later in the fall. Then again, climate change might alter upper level wind patterns, shifting the zone of tropical storm development and impact. Time will tell.
Once a tropical storm develops, favorable conditions, discussed above, may cause it to strengthen into a hurricane. Conversely, if the storm moves into cooler waters, makes landfall or encounters strong upper level winds, the storm dynamics break down and the system weakens or dissipates. In some cases, favorable conditions may be re-encountered and the storm may redevelop; this occasionally occurs in Central America, when Gulf of Mexico storms weaken over land and then re-blossom in the eastern Pacific.
Global warming may extend the hurricane season by producing warm ocean waters earlier in the summer and later in the fall. Then again, climate change might alter upper level wind patterns, shifting the zone of tropical storm development and impact. Time will tell.
Sabtu, 04 Juni 2011
Hominids & the Sahara Desert
The vast Sahara Desert, which stretches across North Africa, began to form in the late Miocene and early Pliocene, some 10 million years ago (MYA). South of this geophysical region, gorillas diverged from the hominid line about 9 MYA and chimpanzees followed 7 MYA. By 4.5 MYA, Australopithecus appeared in the Rift Valley of East Africa and, by 2 MYA, Homo erectus had evolved.
While the Sahara may have been a natural blockade to the northward migration of the earliest hominids, the Pleistocene Epoch (2 MYA to 10,000 YA) brought wide swings in the global climate, marked by four periods of glaciation. During these glacial periods, a cool, wet climate caused the Sahara to contract, opening corridors of savannah that likely permitted ancestral hominids to migrate northward, into Eurasia. Following earlier migrations of Homo erectus, Neandertals began to leave Africa about the time that humans were first appearing, some 150,000 years ago, and occupied Europe by 100,000 years ago. Man remained in sub-Saharan Africa until about 60,000 years ago, when the Wisconsin glaciation permitted migration through northeastern Africa and, due to lowered sea levels, directly across the Red Sea to the Arabian Peninsula.
Nomadic human tribes likely entered parts of the Sahara Desert from the earliest days or our existence but extensive exploration and settlement of that harsh landscape would not occur until the Holocene, aided by the domestication of goats (10,000 YA), sheep (9000 YA), cattle (8000 YA) and dromedary camels (4000 YA). Even today, most human settlements lie in fringe regions of the Sahara and interior towns are limited to natural oases, the Nile Valley and volcanic highlands.
While the Sahara may have been a natural blockade to the northward migration of the earliest hominids, the Pleistocene Epoch (2 MYA to 10,000 YA) brought wide swings in the global climate, marked by four periods of glaciation. During these glacial periods, a cool, wet climate caused the Sahara to contract, opening corridors of savannah that likely permitted ancestral hominids to migrate northward, into Eurasia. Following earlier migrations of Homo erectus, Neandertals began to leave Africa about the time that humans were first appearing, some 150,000 years ago, and occupied Europe by 100,000 years ago. Man remained in sub-Saharan Africa until about 60,000 years ago, when the Wisconsin glaciation permitted migration through northeastern Africa and, due to lowered sea levels, directly across the Red Sea to the Arabian Peninsula.
Nomadic human tribes likely entered parts of the Sahara Desert from the earliest days or our existence but extensive exploration and settlement of that harsh landscape would not occur until the Holocene, aided by the domestication of goats (10,000 YA), sheep (9000 YA), cattle (8000 YA) and dromedary camels (4000 YA). Even today, most human settlements lie in fringe regions of the Sahara and interior towns are limited to natural oases, the Nile Valley and volcanic highlands.
Kamis, 28 April 2011
Tornadoes, Geography & Natural History
The United States, especially that portion east of the Rocky Mountains, is the tornado capitol of the world, as this month has clearly demonstrated. Having served up three times the average number of tornadoes for April and closing in on the all time monthly record of 543, set in May of 2003, the severe weather outbreaks of April, 2011, have produced almost 500 twisters. Yesterday's swath of deadly storms, which stretched from Mississippi to Georgia, was second only to the super-outbreak of April, 1974, and killed at least 170 while leaving a path of destruction almost 300 miles long; more tornadoes are forecast to plague the mid-Atlantic region today.
Lying between a steady source of cool air from Canada and the warm waters of the Gulf of Mexico, the central and southeastern U.S. is often caught in a clash zone as Pacific storms push across the Rockies and intensify over the Great Plains. This scenario, produced by geography and our regional climate, has been in place for at least 70 million years, interrupted only by periods of glaciation, the last of which ended 10,000 years ago.
The weather records by which we compare modern storm systems cover just 200 years, a snapshot in geologic time, and may or may not be significant from the perspective of natural history; needless to say, the destructive power of these recent outbreaks has been of major significance to human communities. Whether episodes of severe weather will increase in concert with global warming is hard to predict but, based on the events of recent decades, it appears that a trend is developing.
Lying between a steady source of cool air from Canada and the warm waters of the Gulf of Mexico, the central and southeastern U.S. is often caught in a clash zone as Pacific storms push across the Rockies and intensify over the Great Plains. This scenario, produced by geography and our regional climate, has been in place for at least 70 million years, interrupted only by periods of glaciation, the last of which ended 10,000 years ago.
The weather records by which we compare modern storm systems cover just 200 years, a snapshot in geologic time, and may or may not be significant from the perspective of natural history; needless to say, the destructive power of these recent outbreaks has been of major significance to human communities. Whether episodes of severe weather will increase in concert with global warming is hard to predict but, based on the events of recent decades, it appears that a trend is developing.
Rabu, 30 Maret 2011
Ocean Currents & Regional Climates
The surface currents of our oceans, which extend to depths of 1500 feet, are determined by wind patterns and the effect of Earth's rotation. In the Northern Hemisphere, the primary oceanic currents flow in a clockwise direction while, in the Southern Hemisphere, they move counterclockwise. Those moving from the Tropics toward the Poles are warm currents and those moving from the Poles toward the Equator are cold currents.
More that a mixing of oceanic waters, these currents have a significant impact on the climate of coastal land areas. The Gulf Stream, for example, carries warm water from the Gulf of Mexico and Caribbean toward the North Atlantic, significantly moderating the climate in Iceland and the British Isles; in like manner, the Japan Current, flowing from Southeast Asia to Alaska, warms the climate of coastal Alaska and British Columbia. Cold currents, such as the Humboldt Current along the west coast of South America, the Benguela Current along the southwest coast of Africa, the California Current along the west coast of North America and the West Australian Current have a cooling effect on these coastal areas and support rich fisheries.
At the Equator, the currents merge into a westward flow while, around the coast of Antarctic, the surface current flows to the east; from these feeder currents, the circling oceanic currents arise. In the Atlantic, the Gulf Stream and Brazil Current carry warm water away from the Equator while the Canaries and Benguela Currents return cooled water from subpolar areas to the Equator. The Indian Ocean surface currents run north along western Australia, west along the coast of India, south along the east coast of Africa and east along Antarctica. In the Pacific, the California and Humboldt Currents, arising in subpolar regions, feed the westward equatorial flow which, at the west edge of the Pacific basin, splits into the warm Japan and East Australian Currents. The climate of any given coastal area is thus a function of both its latitude and the temperature of ocean waters that bathe its shores; of course, the direction of prevailing winds and the presence or absence of nearby mountains will also affect regional weather patterns.
More that a mixing of oceanic waters, these currents have a significant impact on the climate of coastal land areas. The Gulf Stream, for example, carries warm water from the Gulf of Mexico and Caribbean toward the North Atlantic, significantly moderating the climate in Iceland and the British Isles; in like manner, the Japan Current, flowing from Southeast Asia to Alaska, warms the climate of coastal Alaska and British Columbia. Cold currents, such as the Humboldt Current along the west coast of South America, the Benguela Current along the southwest coast of Africa, the California Current along the west coast of North America and the West Australian Current have a cooling effect on these coastal areas and support rich fisheries.
At the Equator, the currents merge into a westward flow while, around the coast of Antarctic, the surface current flows to the east; from these feeder currents, the circling oceanic currents arise. In the Atlantic, the Gulf Stream and Brazil Current carry warm water away from the Equator while the Canaries and Benguela Currents return cooled water from subpolar areas to the Equator. The Indian Ocean surface currents run north along western Australia, west along the coast of India, south along the east coast of Africa and east along Antarctica. In the Pacific, the California and Humboldt Currents, arising in subpolar regions, feed the westward equatorial flow which, at the west edge of the Pacific basin, splits into the warm Japan and East Australian Currents. The climate of any given coastal area is thus a function of both its latitude and the temperature of ocean waters that bathe its shores; of course, the direction of prevailing winds and the presence or absence of nearby mountains will also affect regional weather patterns.
Senin, 24 Januari 2011
La Nina & the Australian Floods
The massive flooding across eastern Australia, which began in November, has been associated with the La Nina phenomenon, which tends to peak every 3 to 7 years. Produced by high pressure over the eastern Pacific and low pressure over the western Pacific, this weather pattern results in strong Pacific trade winds, which bring relatively warm ocean waters to the southeast coast of Asia and the northeast coast of Australia. This spawns strong cyclones and excessive rainfall in these areas, generally during an autumn to autumn cycle in the Southern Hemisphere.
Coinciding with a high Southern Oscillation Index, which measures the seasonal variance of sea surface pressure between Tahiti and Darwin, La Nina episodes trigger excessive precipitation across northern and eastern Australia. This year's flooding has been especially severe, disrupting transportation, stranding inland towns, inundating coal mines and wiping out much of the region's wheat crop. The Great Barrier Reef may also be affected, as plumes from the rivers of northeast Australia sweep particulates and pollutants toward that fragile ecosystem.
The current Australian flooding may prove to be the worst in recorded history. Unfortunately, some climatologists project that the La Nina and the opposite El Nino patterns will intensify with the advance of global warming. For eastern Australia, that could mean an alternating pattern of severe floods and prolonged drought.
Coinciding with a high Southern Oscillation Index, which measures the seasonal variance of sea surface pressure between Tahiti and Darwin, La Nina episodes trigger excessive precipitation across northern and eastern Australia. This year's flooding has been especially severe, disrupting transportation, stranding inland towns, inundating coal mines and wiping out much of the region's wheat crop. The Great Barrier Reef may also be affected, as plumes from the rivers of northeast Australia sweep particulates and pollutants toward that fragile ecosystem.
The current Australian flooding may prove to be the worst in recorded history. Unfortunately, some climatologists project that the La Nina and the opposite El Nino patterns will intensify with the advance of global warming. For eastern Australia, that could mean an alternating pattern of severe floods and prolonged drought.
Minggu, 05 Desember 2010
Evolution of the Sonoran Desert
The Sonoran Desert of the Southwest U.S. and Northwest Mexico is a product of its latitude, the global climate and the regional topography. Lying along one of the desert bands (which run just north and just south of the Tropics), this arid ecosystem receives copious sunshine and is subjected to prolonged periods of high pressure, below which the air is sinking. This atmospheric condition retards cloud formation and both warms and dries the air as it plummets toward the Earth's surface.
Covering a broad basin and surrounded by highlands, the Sonoran Desert is shielded from moisture in all directions; to the northwest are the Sierra Nevada Mountains and the high Mojave Desert, to the north and east is the Mogollon Rim of the Colorado Plateau, to the southeast is the wall of the Sierra Madre Range and, to the southwest, are the mountains of Southern California and the Baja Peninsula. Any air that enters the Sonoran is thus downsloping from higher terrain, causing it to heat up and dry out even further. Since the mountains and plateaus that surround it were uplifted within the past 4 to 20 million years (during the Miocene and Pliocene), the Sonoran Desert is one of the youngest ecosystems on our planet.
Throughout the Pleistocene and into the Holocene, Earth's climate has undergone dramatic shifts. When the climate cooled and glaciers advanced, the area of the Sonoran Desert decreased; in contrast, when the climate warmed (as it has done over the past 10,000 years), the Desert advanced, climbing onto the walls of the adjacent highlands. Throughout these gyrations, the regional flora and fauna have evolved, developing traits that enhanced survival in an arid environment with intense sunshine, cool nights and seasonal rains.
Covering a broad basin and surrounded by highlands, the Sonoran Desert is shielded from moisture in all directions; to the northwest are the Sierra Nevada Mountains and the high Mojave Desert, to the north and east is the Mogollon Rim of the Colorado Plateau, to the southeast is the wall of the Sierra Madre Range and, to the southwest, are the mountains of Southern California and the Baja Peninsula. Any air that enters the Sonoran is thus downsloping from higher terrain, causing it to heat up and dry out even further. Since the mountains and plateaus that surround it were uplifted within the past 4 to 20 million years (during the Miocene and Pliocene), the Sonoran Desert is one of the youngest ecosystems on our planet.
Throughout the Pleistocene and into the Holocene, Earth's climate has undergone dramatic shifts. When the climate cooled and glaciers advanced, the area of the Sonoran Desert decreased; in contrast, when the climate warmed (as it has done over the past 10,000 years), the Desert advanced, climbing onto the walls of the adjacent highlands. Throughout these gyrations, the regional flora and fauna have evolved, developing traits that enhanced survival in an arid environment with intense sunshine, cool nights and seasonal rains.
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