The accumulated remains of marine organisms make much of the deep ocean floor. When these organisms were alive, they would absorb oxygen from the sea water. Scientists can deduce the past ocean temperatures, and therefore global climate by careful analysis of the oxygen in these organic sediments. Studies have shown that oceanic sediments have preserved a record reaching back tens of millions of years, and in older sedimentary rocks the record extends to hundreds of millions of years. Ice Cores
Scientists can directly analyse gases in ice cores from ancient atmospheres. Traces of the ancient atmospheres become trapped and compressed into the ice and the ice retains it there for as long as it remains frozen. Cores drilled through ice sheets contain a record of polar temperatures and atmospheric composition which can range back to 120,000 years in some areas such as Greenland. In places like Antarctica, scientists are able to drill down into the ice and remove cores for chemical analysis, and are able to determine fluctuations of atmospheric gases over the past 800 000 years. Glacial Deposits
Glaciers gouge large amounts of rock and soil from the ground below them as the move slowly. At the end of the glacier the dumped sediment can give a clear indication of its extent. Scientists map the locations of these deposits, and by doing this they are able to work out the past climate in that region. Sea Levels
The amount of water stored at the poles greatly increases when the Earth goes through cooler periods such as ice ages. This is caused by the rise of precipitation falling as ice or snow rather than rain. The snow accumulates on the land in the cooler climate, and becomes permanent ice, so it cannot melt and return to the ocean. As the snow accumulates on the land it removes a huge volume of water from the ocean which causes the sea levels to drop. By looking at shoreline features such as beach ridges, spits and bars, scientists are able to map and date the occurrences of these features and this shows the sea levels of the past. By looking at these shorelines and such, scientists can date the times when the earth went through cooler periods, and therefore can then make a judgement on the carbon dioxide concentration of that time.
By looking at the sources of evidence preserved in geological settings, scientists are able to have a better insight into the patterns of climate change. When it is viewed over long time frames, the climate appears to be a highly variable and cyclic event. According to scientific studies, in past eras atmospheric Carbon Dioxide reached concentrations that were 20 times higher than the current concentration. There have been recent investigations which show that the current change of...