the polar bears as well as humans won't be around forever just like the dinosaurs the most successful species our planet has seen to date
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Historical evidence shows that the climate of the world since the planet was formed more than 4,000 million years ago has fluctuated greatly.
Key Points
* The Earth is currently in the middle of an ice epoch.
* Within an ice epoch there are ice ages, which alternate with shorter warmer periods known as interglacials.
* It is unique for the Earth to have two polar ice caps.
Also in this Series
The Ice Age (Part Two)
Disclaimer
The BBC is not responsible for the content of external websites.
On many occasions the world has borne little resemblance to what we experience today. For example, we are currently in the middle of an ice epoch (longer than an ice age) which has lasted millions of years and is likely to continue for millions more.
Yet, in the context of the history of the planet, this is not a normal period. More average conditions would be significantly warmer, producing the lush vegetation and hot conditions that prevailed aeons ago, when dinosaurs walked the Earth for millions of years.
The reason why we are in the middle of such a cold epoch has a great deal to do with the positioning of the land masses. Almost imperceptibly, the great continents are constantly moving and changing location. Throughout the history of the Earth it has been unusual to have one polar ice-cap; it is unique for us now to have two of them.
Normally the circulation of the warm currents of the oceans helps distribute the heat and ensure a general uniformity of temperatures. However, the land mass that has become known to us as Antarctica has temporarily (in global terms!) positioned itself over the South Pole thereby blocking off warm currents. This has allowed ice some 1,800 metres (6,000 feet) thick to form a sheet over that now most inhospitable of continents.
Similarly, by another quirk of the slow drift of the continents, land has encircled the North pole, causing the waters there to be largely cut off from the worldwide drift of oceanic currents. This too has allowed an ice-cap to develop at the North Pole. Eventually – in tens of millions of years – the land masses of North America and Europe, which are moving away from each other, will be far enough apart to allow the warmer currents from the Atlantic to warm up the Arctic and melt the ice-cap. However, as far as humans are concerned at present the existence of two polar ice-caps is, for all practical purposes, a permanent one.
Within an ice epoch there are ice ages, which alternate with shorter warmer periods known as interglacials. At the moment the Earth is passing through an interglacial period. This has lasted for around 10,000 years following the last Ice Age, which in turn went on for some 100,000 years. It would appear from historical climatic evidence that this ice age/interglacial pattern was established at the beginning of this ice epoch. Perhaps ominously for man, the pattern suggests that ice ages last around 100,000 years on average and the shorter, warmer interglacials around 10,000 – so we are nearing the end of our current warmer period.
However, there is no need for any alarm at this thought. The next ice age could be up to 1,000 years or more away – a short period in climatology but a comfortingly lengthy one for us. And in any case no one can yet predict what effect the greenhouse effect may have on the overall pattern of global cooling and in arresting a return to glacial conditions.
What does seem apparent is that within the current interglacial period, starting some 10,000 years ago, there have been smaller patterns emerging – periods of warmer weather, followed by colder weather and so on. These have been broken down by climatologists into four main periods.
The first followed the end of the last Ice Age, indeed it caused it to end. The Earth probably reached its warmest about 5,000 or 6,000 years ago. At this time the temperature would have been on average about 2C (3.6F) warmer than the present day.
This period has acquired the name the Optimum period as a result, and was followed by a much colder spell. This more or less coincided with the historical period called the Iron Age, which reached its coldest around 2,500 years ago. (It should be remembered that these changes are gradual and do not occur overnight).
------------------------------------------------
Historical evidence shows that the climate of the world since the planet was formed more than 4,000 million years ago has fluctuated greatly.
Key Points
* The Earth is currently in the middle of an ice epoch.
* Within an ice epoch there are ice ages, which alternate with shorter warmer periods known as interglacials.
* It is unique for the Earth to have two polar ice caps.
Also in this Series
The Ice Age (Part Two)
Disclaimer
The BBC is not responsible for the content of external websites.
On many occasions the world has borne little resemblance to what we experience today. For example, we are currently in the middle of an ice epoch (longer than an ice age) which has lasted millions of years and is likely to continue for millions more.
Yet, in the context of the history of the planet, this is not a normal period. More average conditions would be significantly warmer, producing the lush vegetation and hot conditions that prevailed aeons ago, when dinosaurs walked the Earth for millions of years.
The reason why we are in the middle of such a cold epoch has a great deal to do with the positioning of the land masses. Almost imperceptibly, the great continents are constantly moving and changing location. Throughout the history of the Earth it has been unusual to have one polar ice-cap; it is unique for us now to have two of them.
Normally the circulation of the warm currents of the oceans helps distribute the heat and ensure a general uniformity of temperatures. However, the land mass that has become known to us as Antarctica has temporarily (in global terms!) positioned itself over the South Pole thereby blocking off warm currents. This has allowed ice some 1,800 metres (6,000 feet) thick to form a sheet over that now most inhospitable of continents.
Similarly, by another quirk of the slow drift of the continents, land has encircled the North pole, causing the waters there to be largely cut off from the worldwide drift of oceanic currents. This too has allowed an ice-cap to develop at the North Pole. Eventually – in tens of millions of years – the land masses of North America and Europe, which are moving away from each other, will be far enough apart to allow the warmer currents from the Atlantic to warm up the Arctic and melt the ice-cap. However, as far as humans are concerned at present the existence of two polar ice-caps is, for all practical purposes, a permanent one.
Within an ice epoch there are ice ages, which alternate with shorter warmer periods known as interglacials. At the moment the Earth is passing through an interglacial period. This has lasted for around 10,000 years following the last Ice Age, which in turn went on for some 100,000 years. It would appear from historical climatic evidence that this ice age/interglacial pattern was established at the beginning of this ice epoch. Perhaps ominously for man, the pattern suggests that ice ages last around 100,000 years on average and the shorter, warmer interglacials around 10,000 – so we are nearing the end of our current warmer period.
However, there is no need for any alarm at this thought. The next ice age could be up to 1,000 years or more away – a short period in climatology but a comfortingly lengthy one for us. And in any case no one can yet predict what effect the greenhouse effect may have on the overall pattern of global cooling and in arresting a return to glacial conditions.
What does seem apparent is that within the current interglacial period, starting some 10,000 years ago, there have been smaller patterns emerging – periods of warmer weather, followed by colder weather and so on. These have been broken down by climatologists into four main periods.
The first followed the end of the last Ice Age, indeed it caused it to end. The Earth probably reached its warmest about 5,000 or 6,000 years ago. At this time the temperature would have been on average about 2C (3.6F) warmer than the present day.
This period has acquired the name the Optimum period as a result, and was followed by a much colder spell. This more or less coincided with the historical period called the Iron Age, which reached its coldest around 2,500 years ago. (It should be remembered that these changes are gradual and do not occur overnight).