Climate Change: Long, Medium and Short Term
Long term evidence:
Type of evidence
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
| 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...
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