Climate Change Evidence
Climate Change: Long, Medium and Short Term
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 | | |
Medium-term evidence: 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
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 | | |
Medium-term evidence: 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