Climate Overview Of The Last 20,000 Years
Last Glacial Maximum- a time, around 20,000 years ago, when much of the Earth was covered in ice. The average global temperature may have been as much as 10 degrees Celsius colder than that of today. The Earth has a long history of cycles between warming and cooling. Currently we are in an interglacial period where warming has occurred for about 15,000 years.
Change in Climate
Milankovitch Effect- Theory that states that slow changes in the Earth?s orbit cause changes in the seasonal cycle of solar radiation. As the Earth?s orbit changes, the amount of insolation that the northern hemisphere receives increases or decreases depending on how the Earth is tilted on its spin axis. When the northern hemisphere receives less insolation, the surface temperature begins to fall slightly, triggering a cycle of global cooling.
Ice-Albedo Effect- a process in which the surface temperature of the Earth decreases because the ice reflects the incoming radiation. As the ice continues to reflect solar radiation, the global temperature decreases causing growth in the ice sheets that covered much of the Earth. This process describes a positive feedback loop.
- complex series of climatic & environmental changes of varying intensity and duration
A Look at Europe
22,000 - 14,000 B.P. (before present)
- human?s in central Europe experienced dramatic changes in climate and environment
- last major advance of ice sheets
- most severe ice-age conditions of Pleistocene epoch
- 18,000 B.P. Conditions of extreme aridity & severe cold
- much of region uninhabitable by humans, yet human presence still persisted
Last Glacial Maximum in Europe
- annual mid latitude surface 10 degrees Celsius less than present
- estimated winter temperatures 15 - 20 degrees below present values
- Global surface wind increased 20 - 50% or more
- Precipitation at poles decreased by 50%
- Parts of western & central Europe reduced to polar desert
- Significant deglaciation did not begin until 13-14,000 B.P.
Holocene - post-glacial epoch (25,000 - 10,000 years ago)
- until about 10,000 years ago, glacial climate made Earth cold
- Canada buried beneath several km of ice
- Europe had no forests
- Southeast Asian islands were joined to form a single land mass
- Present epoch is latest of a series of warmer intervals
- Last glacial period reached a peak between 25,000 and 18,000 years
- Under full glacial climate Ice sheets over 4km thick lay over n. Europe & N. America
- Smaller ice caps existed in alps
- onset of Holocene witnessed the start of environmental processes which have continued up to present day;
processes such as soil formation, plant successions
Ice Sheets & Sea Levels
- retreat of ice sheets caused sea levels to rise from -55 m at 115000 B.P. to around modern elevations
- adjustment and adaptation
- significant rapid climate change during deglaciation of North Atlantic
- Scientists speculate cooling may have been caused be release of fresh water trapped behind ice on North America
into Atlantic Ocean
- brief return to glacial conditions during time of deglaciation
- Climate return to prior condition & continued general warming to present day conditions
- Led to enormous but short lived changes in Northern Europe
- Change from Forests to herbaceous plants, back to forests
* Challenges previous idea that climate could only change very gradually
* Demonstrates change can be abrupt
* Stresses on system build up and sudden fundemental changes occur
Climate and the rise of Human Civilization
I. Early Human Migration
A. First early humans, Homo sapiens Neanderthals, came upon the scene 350,000 years ago replacing Homo erectus
1. Spread across Europe, Asia and Africa
2. Primitive tool-making and fire
3. Hunted big game, primitive bison, woolly mammoth, etc.
B. Between 40,000 and 35,000 years ago, Homo sapiens
sapiens appeared suddenly in Africa.
1. Spread to Asia and Europe
2. Quickly absorbed or replaced all previous Homo sapiens species and occupied every previously inhabited space.
C. Humans migrated for food.
1. When food source was depleted, they migrated to find more food
2. Can trace the movement of humans to the migratory patterns of big game
3. Early humans had no knowledge of useful land cultivation
4. Climate limited cultivable land
A. As early as 30,000 until 12,000 years ago the Bering Strait
was dry land, a vast northern lowland known as Beringia
1. Focalized species found in both Asia and North America.
B. At the height of the last glaciations three large continental glaciers in Europe, Greenland, and North America contained a significant amount of Earth's water. Enough that sea levels were at least 280 feet lower than today.
C. 12,000 years ago Asia and North America were separated and humans began migrating into the Americas.
D. Human could have colonized both North and South America in approximately 1000 years.
III. Climate and early human development
A. Warming period - significant global warming of 4-5
degrees Celsius of the last 15,000 years, marks the recovery of the earth
from the last ice age.
1. Period we're currently in called an interglacial.
2. The current warm period begun roughly 10,000 years ago is known as the Holocene interglacial
3. Onset and recovery of ice-age conditions is attributed to the Milankovitcth effect
4. This warming period allowed for a larger amount of land to be used for farming cultivation.
- The earth has been introduced to a species that is very unique.
They are able to manipulate the environment with simple tools and technology.
Able to occupy any climatic and environmental region with invention like
fire, clothes, and man-made structures. They have no natural predators
1. The human population explodes
2. See rise in population growth in Fertile Crescent, now known as the Middle East, about 10,500 years ago. Population boom in China around 7500 B.C. and Central America one around 3500 B.C.
A. The direct result in agricultural advance was a trend toward higher
production of food in increasingly more concentrated areas.
1. Shifting cultivation
3. Animal domestication
B. An increase in food led to an increase of people in ever more
densely populated areas
C. People began to specialize in social function; smiths, merchants, etc. They weren't burdened by having to grow their own food.
D. Areas began to organize into markets, states and religious cults
E. Through trade, wars and migration with neighboring civilizations, technology and ideas also flourished
F. Because of specializations and organization there was a rise in the differences in power, to a process of social stratification.
G. These early society become more or less the same models of societies we see today.
(Past 20,000 Years)
- the biggest event in the Pacific Northwest history during this time period, was the physical creation of the area as it looks today
Last Glacial Maximum (22,000 - 10,000 years ago)
- Ice sheets covered most of the earth
- Over 1/2 the world is ice
1. Laurentide Ice Sheet
2. Cordillerian Ice Sheet
- Puget Lobe formed Puget Sound
- Okanogan Lobe formed Columbia Plateau
1. Classic Ice Age cave man story
Ice Sheet facts:
- 50-60 million km^3 of water from oceans froze
* sea levels 125 meters lower
- Atmospher3e very arid - Precipitation levels drop 50%
- Global temperature decrease by 5-6 degrees Celsius
- Mountain snow levels decrease by 1 km
- Forests and woodlands nearly non-existent
- Global winds 20-50% stronger
- Best Guess: Milankovich cycles
- Ice / Albedo Feedback
Retreat of Glaciers:
- Massive flooding as ice dams break
- Mineral & Sediment deposits
In the Pacific Northwest, the most recent ice age began about
30,000 years ago and ended only 11,000 years before present. It is
known as the Fraser Glaciation and began with the growth of local alpine
valley glaciers which peaked about 20,000 years ago. By 18,000 years
ago a continental glacier began its advance into the North Cascades from
Canada. The major ice sheet - the Cordilleran ice sheet - extended
farthest along major south-trending valleys and lowlands between Canada
and the US. It formed several lobes segregated by highlands and mountain
ranges. The south-westernmost extension of the Cordilleran ice sheet
was known as the Puget lobe. Cordilleran ice advanced southward into
the Puget lowland and across southeastern Vancouver Island about 18k,000
years B.P. The ice sheet advanced to the western Strait of Juan de
fuaca by about 17,000 years BP and to the Seattle area after 15,000 years
BP. It went down as far as Olympia and retreated northward past the
Seattle area by 13,650 years BP. About 15,000 years ago the ice sheet
grew to more than a mile thick and covered all but the highest peaks in
the area. During its maximum stand the cordilleran ice sheet buried
much of the northeastern North Cascade Range.
The Puget lobe last advanced into the Puget Lowland of western Washington about 15,000 years ago. It left behind a varied record of both depositional and erosional landforms. These landforms still dominate the landscape of the region. Most prominently, the advancing ice sheet deposited voluminous sediment on a pro-glacial outwash plain that extended from the Olympic Mountains to the Cascade Range. This plain is known as the great lowland fill. The fill was overrun by the ice sheet and this overrunning modified the surface in several ways, one of which was by the excavation of deep linear troughs, which are now occupied by large lakes and the marine waters of Puget Sound. The carving of these huge troughs was the most dramatic alteration to the landscape. Up to 1200 feet deep, the troughs were carved into the level out-wash plain beneath the Puget ice lobe. Throughout several thousands of years that the iced mass occupied Puget Sound, large amounts of glacial melt water were discharged from under the glacier carrying away more than 250 cubic miles of sediment excavation 10 troughs into the bed under the glacier. The passage of ice through the lowlands left the deep channels known today as Admiralty Inlet, Hood Canal, Possession Sound, Puget Sound, the Western Strait of Juan de Fuca, Lakes Washington and Sammammish, as well as an intricate network of smaller canals and inlets all part of an elaborate glacial waterway.
Excavation of the troughs and valleys of the Puget Lowland required the transport of about 1,000 cubic kilometers of sediment, almost entirely during ice occupation and primarily by sub-glacial water. The landscape we see today is largely a result of the repeated cycles of glacial scouring and deposition, followed by subsequent non-glacial processes, such as land-sliding, stream erosion and deposition, weathering, and wave action. The north-south hills of Seattle, and throughout the region, are the result of glacial scouring and sub glacial stream erosion, as are the deep troughs that underlie the waters of Puget Sound.
1. Columbia River Plateau covers much of northeast Oregon and southeast Washington. Part of it extends into Idaho into the Coeur d' Alene area, which is located just outside of Spokane. Most of the Columbia Plateau consists of desert as well as mountains located in the lower half of Washington and Northeastern Oregon
2. The plateau consists of the Blue Mountains, Clearwater Mountains, and other foothills in the middle of Washington and Northeast Oregon. All of these created from the lava flows millions or thousands of years ago.
3. Hundreds of lava flows have been the cause for creating the Columbia plateau, which occurred back during the middle of the Miocene era dating back 17million years ago. Many of the canyons created were from the end of the ice age where enormous lakes in Montana would overflow sending millions of gallons of water into Idaho and Washington. These giant floods would cut away at the basalt. It would travel over the basalt and finally reaching its final destination at the Pacific Ocean.
basalt - a hard, dense, dark volcanic rock composed chiefly of plagioclase, pyroxene, and olivine, and often having a glassy appearance
4. These huge water flows from Lake Missoula would create canyons, which the Snake and the Columbia River would be flowing through later on, resulting in canyons up to 3000 ft high. Today you can still find gravel deposits and channels leftover from the Lake overflowing its banks.
5. From the glaciers receding as well as the floods, there are many sediment basins located all around Eastern Washington and Northeastern Oregon.
6. Some of the wildlife in the Columbia Plateau included animals
such as the painted turtle; the ox-sized rhino, which is smaller than today's
modern rhino, that and it had two horns instead of one.