Proxy Measurements - A Window To The Past

This post is again focusing on the methods used to map the variation in Earth’s climate over its history and this time we’ll be focusing on the use of proxy measurements.

Proxy measurements take many forms and can provide information on climate for a few hundred years up to many millions of years. However like the measurements currently being used which were discussed in the last post each method has its own flaws.

So the first methods which most of you will have heard of is the use of tree rings or dendrochronology, this method has many benefits for instance trees can be found nearly on every continent an

d so a good spread of data can be gathered. However there are drawbacks the width of tree rings are not solely affected by temperature factors such as rain, soil temperature and age will also have an influence and so need to be considered. Through research we have been able to learn that conifer tree ring width changes exponentially with age so this can be compensated for. Other tree species ring width are not so easy to read however such as Oaks, this is a drawback as species such as Oaks tend to have a longer life span and so can provide more data when sampled.

A second method used to monitor climate change is through the use of Ice cores. These provide general information on climate across the global due to the isotope composition within the layers. There are several different Oxygen isotopes (O¹⁶ and O¹⁸) and it is the composition of these isotopes within the ice cores which suggest historic temperature. This is possible due to the fact that each isotope has a slightly different boiling temperature and so the ratios which they are found within the ice cores give a suggestion to the previous temperature at the equator which is where the majority of water evaporates from to create the snow at the poles. There are again problems with ice cores however for instance they can only be found in certain locations. Along with this they can be affected by water flowing through the ice layers disrupting the isotope composition, these ratios can also be affected where the ice touches the bedrock. Dating the layers can cause issues as they require a significant event such as a volcano to lay down ash so as to act as a time point within the ice layers otherwise samples cannot be used as they are not accurate enough. Finally ice cores can capture gas bubble within them and these give information about the atmospheric composition in the past and so suggest at historic temperatures.

A further method which many of you won’t have heard of is the use of soil sediments magnetism to provide temperature data. This has been put to use in China with sediment known as loess. Temperature and rainfall effect how magnetic the sediment is and so historic temperature can be extrapolated from these levels as warmer wetter years create a higher level of magnetism. The drawback with this method however is the fact that sites where this is possible are extremely limited.  

There are many other methods which have been used to provide accurate measurements on historic temperatures. Further methods include pollen and fossil records, Ocean sediments, stalactites and stalagmites CaCO₃ composition to name just a few. Each of which has their own drawbacks and benefits and so as a collective they provide an almost complete image of earth climate variation.

Thanks for reading!

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