Long term evidence:
Type of evidence| Explanation| Reliability|
Ice cores – CO2| CO2 trapped in ice cores. Low concentrations of CO2 occur naturally during glacial periods and high concentrations during interglacial periods (present). 2007 measured 383 parts per million.| The number of CO2 sequences that correlate well with each other suggest it is reliable.| Ice cores – O2 isotopes| Ratio of oxygen 16 to 18 is a good indicator of past sea levels. In glacial periods oxygen 16 evaporation more from oceans which became enriched with oxygen 18. Ice from glacial periods is enriched with oxygen 16.| The number of oxygen isotope records that broadly agree on sea level changes is high and the correlation with CO2 is good.| Pollen analysis| Pollen taken from sediment cores in peat bogs and lake beds. Pollen grains kept in waterlogged sediments. Different pollen from different plants can be identified. | Relies on preservation of pollen. Long pollen sequences are rare and vegetation may fall behind climate change.| Past glacial/sea level change| | |
Type of evidence | Explanation | Reliability |
Historical records| Analysis paintings, photos and sequences from many years ago. E.g. written accounts such as Greenland Sagas. They show past climates such as Little Ice Age and Medieval Warm Period.| Unreliable since they were not made to record climate and are also local sources. | Tree rings| Trees are sensitive to annual changes in temperature, sunlight and rain. Thickness of annual growth rings records climatic conditions.E.g. wide rings show good growing conditions| Accuracy is good but too local and is hard to determine the relevant importance of the climate.| Retreating glaciers | Valley glaciers grow and shrink due to climate. Can be tracked by old paintings, photos, maps, and taking direct measurements of snout or moraine positions. Most glaciers reached...