Global climate change Evidence & Causes

Global climate change Evidence & Causes

1. Evidence

   • Pollen analysis
     • Species have climate requirements that influence their geographical distributions. each plant species has a distinctively shaped pollen grain and if these fall into oxygen-free environments such as peat bogs, they resist decay.
       • Changes in the pollen found in different levels of the bog indicate changes in climate over time.
         • one limit to this is that pollen can be transported considerable distances by wind and sometimes wild life.
   • Dendrochronology
     • The analysis of tree rings from core samples. each year the growth of a tree is shown in its trunk by a single ring made up of 2 bands. : a band for reflecting rapid spring growth when cells are larger and a band for narrower band of growth during the cooler autumn,
       • the width of the ring depends on the conditions of each year. A wide band indicates a warm and wet year, narrower one cooler and dry conditions. recent investigations however have shown that trees respond more to levels of moisture than temperature. Dendrochronology has a limitation in that few trees are older than about 4000 years. It has been possible to extend surveys futher back by using remains of vegetation preserved in non oxygen conditions.
   • Ice Core analysis
     • Glacial ice can be studied by drilling cores from areas such as Antarctica and Greenland. The carbon dioxide trapped within the ice is a climatic indicator- levels tend to be lower during cooler periods and higher when it is warmer. another method is to look at oxygen isotope levels.
   • Radio Carbon dating
   • Coleoptera
     • Remains of Coleoptera beetles are common in freshwater and land sediments. different species of this beetle tend to be found under different climatic conditions. knowledge of the present climatic range of the different species and the age of sediments in which remains are found, allows past climatic conditions to be determined.
   • Changing sea levels
     • the presence of rias and Fjords indicates rising (eustatic) sea levels flooding glacial and river valleys. changes in sea levels are indicators of climate change- the volume of sea water changes as it warms/ cools.
   • Glacial deposits
     • these show records of ice advance during colder periods and retreat during warmer times.
   • Historical records
     • historical records include cave paintings, depth of grave digging in Greenland, diaries, documentary evidence of events (such as frost fairs on the Thames) and evidence of areas former vine cultivation. since 1873 daily weather reports have been documented, and the royal society has encouraged the collection of data since the 17th century, parish records are a good source of climate data.
   • Recent evidence of global warming
     • Recent figures show the average world temperature has risen since records were first kept in 1860. Although the overall rise seems small, the 10 hottest years have all occurred since 1980 and the 1990s was the hottest decade. the 1st years of the 21st century continued the trend and global warming has probably become the major environmental issue of our time. Although scientists have been slow to commit themselves about cause and effect, there is no doubt the planet is heating up.
   • Sea floor analysis
     • Core samples from the ocean floor reveal shifts in animal and plant populations which indicate climate change. the ratio of the isotopes: oxygen is 18:16. similar to ice core analysis during colder phases, when water evaporated from the oceans and precipitated onto the land, it eventually forms glacial ice water containing lighter oxygen 16. this is more easily evapourated than oxygen 8. as a result, oceans have a higher concentration of oxygen 18 compared to sheets and glaciers containing oxygen 16
       • recent studies suggest isotope variations are an indication of changes in the volume of ice rather than water temperature but as the ice volume itself reflects climatic conditions, such studies have tended to confirm earlier findings.

2. The climate of the British Isles has changed significantly since the Pleistocene Ice age, which ended around 10'000 or 11'000 years ago. at the end of the Pleistocene, in the period known as the Pre-Boreal, the climate began to warm up and that trend has continued ever since. There have however been some fluctuations during which the climate began