Post by Babylon Enigma on Aug 26, 2010 20:01:35 GMT -5
Our planet has been inhabited by complex life for 600 million years. During most of that period, Earths temperature levels and Carbon dioxide concentrations have been several times higher. Here is an estimation(smoothed graph) of Earths past climate.
You will notice in the graph, that our present temperatures are very cool compared to the typical trend of the past. Roughly 3 million years ago, the Earth began to cool and entered a cycle called interglacial period. We are currently in such a cycle. During these cycles, the Earth enters an ice age for thousands of years, then warms up for thousands of years(interglacial=between glacial), then enters an ice again which is followed by another warm(interglacial) period again thus repeating the process on and off. For the last 400,000-500,000 of years, ice ages have lasted about 100,000 of years and the interglacial periods have lasted 10,000-12,000 years.
Interglacial
An interglacial is a geological interval of warmer global average temperature that separates glacial periods within an ice age. The current Holocene interglacial has persisted since the end of the Pleistocene, about 11,400 years ago.
From ice core data
Interglacials during the Pleistocene
During the 2.5 million year span of the Pleistocene, numerous glacials, or significant advances of continental ice sheets in North America and Europe have occurred at intervals of approximately 40,000 to 100,000 years. These long glacial periods were separated by more temperate and shorter interglacials.
During the interglacials, one of which we are in now, the climate warmed to more or less present day temperatures and the tundra receded polewards following the ice sheets. Forests returned to areas that once supported the tundra vegetation. Traditionally, interglacials have been identified on land or in shallow epicontinental seas by their paleontology. Floral and faunal remains of species pointing to temperate climate and indicating a specific age are used to identify particular interglacials. Most used are mammalian and molluscan species, pollen and plant macro-remains (seeds and fruits). However, many other fossil remains may be helpful: insects, ostracods, foraminifera, diatoms, etc. More recently, ice cores and ocean sediment cores have provided more quantitative and better dated evidence for temperatures and total ice volumes.
Interglacials are a useful tool for geological mapping and also for anthropologists, as they can be used as a dating method for hominid fossils.[1]
Brief periods of milder climate that occurred during the last glacial are called interstadials. Most (not all) interstadials are shorter than interglacials. Interstadial climate may have been relatively warm but this is not necessarily so. Because the colder periods (stadials) have often been very dry, wetter (so not necessarily warmer) periods have been registered in the sedimentary record as interstadials as well.
The oxygen isotope ratio obtained from deep sea cores and a proxy for average global temperature, is an important source of information about changes in the climate of the earth.
Interglacial optimum
An interglacial optimum, or climatic optimum of an interglacial, is the period within an interglacial that experienced the most 'favourable' climate that occurred during that interglacial, often during the middle part. The climatic optimum of an interglacial follows, and is followed by, phases that are within the same interglacial and that experienced a less favourable climate (but nevertheless a 'better' climate than during the preceding/succeeding glacials). During an interglacial optimum, sea levels rise to their highest values, but not necessarily exactly at the same time as the climatic optimum.
In the present interglacial, the Holocene, the climatic optimum occurred during the Subboreal (5 to 2.5 ka BP) and Atlanticum (8 to 5 ka). Our current climatic phase following this climatic optimum is still within the same interglacial (the Holocene).
The preceding interglacial optimum occurred during the Late Pleistocene Eemian Stage, 131–114 ka. During the Eemian the climatic optimum took place during pollen zone E4 in the type area (city of Amersfoort, Netherlands). Here this zone is characterized by the expansion of Quercus (Oak), Corylus (Hazel), Taxus, Ulmus (Elm), Fraxinus (Ash), Carpinus (Hornbeam), and Picea (Spruce). During the Eemian Stage sea level was about 8 meters higher than today and the water temperature of the North Sea was c. 2°C higher than at present.
en.wikipedia.org/wiki/Interglacial
You will notice in the graph, that our present temperatures are very cool compared to the typical trend of the past. Roughly 3 million years ago, the Earth began to cool and entered a cycle called interglacial period. We are currently in such a cycle. During these cycles, the Earth enters an ice age for thousands of years, then warms up for thousands of years(interglacial=between glacial), then enters an ice again which is followed by another warm(interglacial) period again thus repeating the process on and off. For the last 400,000-500,000 of years, ice ages have lasted about 100,000 of years and the interglacial periods have lasted 10,000-12,000 years.
Interglacial
An interglacial is a geological interval of warmer global average temperature that separates glacial periods within an ice age. The current Holocene interglacial has persisted since the end of the Pleistocene, about 11,400 years ago.
From ice core data
Interglacials during the Pleistocene
During the 2.5 million year span of the Pleistocene, numerous glacials, or significant advances of continental ice sheets in North America and Europe have occurred at intervals of approximately 40,000 to 100,000 years. These long glacial periods were separated by more temperate and shorter interglacials.
During the interglacials, one of which we are in now, the climate warmed to more or less present day temperatures and the tundra receded polewards following the ice sheets. Forests returned to areas that once supported the tundra vegetation. Traditionally, interglacials have been identified on land or in shallow epicontinental seas by their paleontology. Floral and faunal remains of species pointing to temperate climate and indicating a specific age are used to identify particular interglacials. Most used are mammalian and molluscan species, pollen and plant macro-remains (seeds and fruits). However, many other fossil remains may be helpful: insects, ostracods, foraminifera, diatoms, etc. More recently, ice cores and ocean sediment cores have provided more quantitative and better dated evidence for temperatures and total ice volumes.
Interglacials are a useful tool for geological mapping and also for anthropologists, as they can be used as a dating method for hominid fossils.[1]
Brief periods of milder climate that occurred during the last glacial are called interstadials. Most (not all) interstadials are shorter than interglacials. Interstadial climate may have been relatively warm but this is not necessarily so. Because the colder periods (stadials) have often been very dry, wetter (so not necessarily warmer) periods have been registered in the sedimentary record as interstadials as well.
The oxygen isotope ratio obtained from deep sea cores and a proxy for average global temperature, is an important source of information about changes in the climate of the earth.
Interglacial optimum
An interglacial optimum, or climatic optimum of an interglacial, is the period within an interglacial that experienced the most 'favourable' climate that occurred during that interglacial, often during the middle part. The climatic optimum of an interglacial follows, and is followed by, phases that are within the same interglacial and that experienced a less favourable climate (but nevertheless a 'better' climate than during the preceding/succeeding glacials). During an interglacial optimum, sea levels rise to their highest values, but not necessarily exactly at the same time as the climatic optimum.
In the present interglacial, the Holocene, the climatic optimum occurred during the Subboreal (5 to 2.5 ka BP) and Atlanticum (8 to 5 ka). Our current climatic phase following this climatic optimum is still within the same interglacial (the Holocene).
The preceding interglacial optimum occurred during the Late Pleistocene Eemian Stage, 131–114 ka. During the Eemian the climatic optimum took place during pollen zone E4 in the type area (city of Amersfoort, Netherlands). Here this zone is characterized by the expansion of Quercus (Oak), Corylus (Hazel), Taxus, Ulmus (Elm), Fraxinus (Ash), Carpinus (Hornbeam), and Picea (Spruce). During the Eemian Stage sea level was about 8 meters higher than today and the water temperature of the North Sea was c. 2°C higher than at present.
en.wikipedia.org/wiki/Interglacial