Changes+in+the+amount+of+ice

__**Temperature fluctuations:**__

Temeprature has changed changed over time. At present, we are particularly concerned about global warming and the impacts it may have on our weather and on sea levels. The current trend of warming may be linked to human activities, climate change in the past has been entirely natural.

The most likely causes are:
 * subtle variations in the earth's orbit
 * slight changes in its tilt towards the sun
 * variations in the global pattern of ocean currents, which move heat around the world

At present, slight chnages in the ocean currents of the west coast of South America result in the **El Nino effect**. This has a significant impact on patterns of rainfall and on the development of tropical storms in some parts of the world.

BBC video explain why the amount of ice changes - []

Climate change during the Pleistocene period:

Hippo's used to live in the River Thames a 100,000 years ago. Temperatures have fluctuated and the climate in the UK used to be like that of modern day East Africa a 100,000 years ago.

Geological time is divided into periods. The most recent is called the Pleistocene period. The last 10,000 years is known as the Holocene. The Pleistocene is characterised by long glacial periods and shorter warmer periods and lasted approximately 2 million years.




 * Glacials:** a period of cooler climates where the amount of ice increased


 * Interglacials:** a period of warmer climates where the amount of ice decreased


 * __How do we know that temperatures fluctuated?__**

Evidence from ice cores and deep sea sediments suggests there may have been as many as 20 cold periods or glacials during the Pleistocene period. media type="youtube" key="eC1JtFQcvD0" height="344" width="425"media type="youtube" key="OmGNaSHDWGU" height="344" width="425" The two youtube videos above discuss how ice cores are taken and then used to reconstruct past climates.

During the **cooler** **glacial periods:** Between the glacial periods there were **warmer interglacials** which were at least as warm as today's climate if not warmer.
 * ice advanced south in the Northern Hemisphere to cover large parts of Europe and North America
 * 18,000 years ago the ice reached its maximum extent during the last Glacial period
 * in the UK the ice in the UK spread as far south as the Severn estuary
 * southern England would have been completely frozen - like parts of northern Canada today

Description of ice coverage 18,000 years ago: The ice covered large areas of the northern hemisphere. All of Canada and a large part of the USA were covered by the Laurentide ice sheet. In Europe most of the UK and all of Scandinavia was covered in ice. The ice spread down through Germany and the Baltic states. Ice also spread across most of northern Russia. Ice spread from mountain ranges such as the Alps in Europe, the Himalyas in Asia and the Andes in South America this is due to the higher altitude where it is colder.
 * Maximum global ice coverage 18,000 years ago**


 * Ice coverage over the British Isles 18,000 years ago**

Description of ice coverage in the UK 18,000 years ago: The ice spread from mountainous areas in the UK such as the Lake District and Snowdonia and from Scandinavia. In the UK the ice covered most of Wales and the eastern side of the UK.

For the exam you should make sure you can describe the extent (size) and causes of the fluctation in ice coverage.

Currently there are two large areas of ice in the world called **ice sheets.** The largest ice sheet is in Antarctica and covers an area of 14 million sqkm and holds 90% of all fresh water on the earth's surface. In several places it is several kilometres thick.

The Greenland ice sheet covers an area of 1.7 million sqkm thick and is currently melting due to global warming.

The present-day distribution of ice sheets and ice caps

Smaller bodies of ice covering an area less than 50,000 sqkm are called **ice caps or ice fields**. They are usually found in mountainous areas where the temperatures are lower, such as Iceland and the European Alps. Spreading out from ice caps are individual 'fingers' of ice called **glaciers**. They often follow former river valleys and extend down to an altitude where melting converts the ice to running waters. Glaciers are found in every continent in the world and in some 47 individual countries.

The glacier on top of Mount Kilamanjaro.


 * __Examples of real glaciers:__**

Baltoro glacier - Pakistan Peritio Moreno Glacier - Argentina Grosser Aletsch Glacier - Switzerland Schlatenknees Glacier - Austria Easton Glacier - Rocky Mountains, USA


 * Key terms:**

Glacial: a period of ice advance associated with falling temperatures Interglacial: a period of ice retreat associated with rising temperatures Ice sheet: a large body of ice over 50,000 sqkm in extent Ice cap: a smaller body of ice (less than 50,00 sqkm usually found in mountainous regions Glacier: a finger of ice usually extending downhill from an ice cap occupying a valley