7.2 - Evidence for Climate Variations (Recent) Flashcards
Ice cores containing gas bubbles and oxygen isotopes
Ice in glaciers retains a record of the climate when it forms. As snow falls in glacial areas it is compacted by later snowfall to form ice.
Ice cores provide data about the concentration of atmospheric gases such as carbon dioxide, methane and oxygen from gas bubbles trapped in the ice. Ratios of oxygen isotopes have been measured which correlate with specific temperatures and climates, creating standards. The ratios in the ice cores are analysed against these standardised ratios, determining the temperature when particular layers of the ice core formed, creating records of global temperatures and climate change across this period of time. Carbon dioxide can also be used in this way as more CO2 in a particular layer of the ice core indicates the climate was warmer in the past, and less CO2 in a layer indicates that the climate was cooler in the past.
Dendrochronology
Dendrochronology works on the principle that each year, a tree puts a ring of growth marked by big cells grown in summer and then smaller cells grown in the colder months. The width of an annual growth ring indicates the quality of the growing season - wide rings indicate warm, wet conditions, while narrower rings may be due to drought or other adverse conditions, such as darkened skies due to volcanic ash. A living tree can be used as a record of the climate during its life, giving year by year data on the quality of the growing season. To go back further in time than the age of a single tree, older specimens of timber found in swamps, timber ships, buildings etc, can be matched to younger timber to give a continuous sequence. This method of calculating climate can only be used reliably for recent climates due to the lifespan of trees and the difficulty of piecing together a continuous sequence as you go back further in time.
Aboriginal art sites showing now-extinct species and environments
Aboriginal rock art depicts changing ecosystems and species which are now extinct. Underwater caves showing evidence of occupation by Aboriginal people and oral histories are linked to rising sea levels along coastal plains, indicating a change to a warmer climate. Aboriginal art drawings include animals and environments that change with the age of the art, and so provide evidence for climate variation as species can only live in particular climates. An example of this is the extinct megafauna, where the rock art illustrates that the megafauna died out as the climate was changing. The rock that the art was done upon can be dated to give an absolute date to the presence of the organisms pictured.
human instrumental records
Instrumental records made with scientific instruments such as thermometers for temperature, barometers for pressure and rain gauges provide important data about climate but they only provide information over large areas for the last few hundred years. For example, although thermometers were invented in the mid 1600s, it was not until the early 18th century that reliable instruments and appropriate temperature scales were developed.
There are many historical written comments about weather events since European colonisation, but as a scientific database, these descriptions are not very reliable since they may show bias by focusing on extreme events such as hot days or floods.
isotope ratios shown in stalagmites, stalactites and corals
Cave structures and corals contain annual growth rings that can be dated.
In caves, water saturated with dissolved CO2 precipitates calcium carbonate as it drips from a cave roof onto the floor, creating speleothems such as stalagmites and stalactites. They detail changes in precipitation and temperature from quite recently to almost half a million years ago. Oxygen and carbon isotopes –> same as ice cores.
Corals provide information about the climate of the shallow oceans in which they live. Oxygen isotopes are analysed from the layers of the coral to determine changes.
