Dating is important for understanding past (and future) climate change

Dating is important for understanding past (and future) climatic change because the climate system is incredibly complicated, with interactions between ocean currents and temperatures, the size and elevation of landmasses and ice-masses, the strength of winds, volcanic activity, the atmospheric composition of gases and even the distance of the earth from the sun influencing the climate that we experience.

Measurements of weather and climate (long-term trends in weather) since the 1860s have enabled us to know that our climate is changing, however what is still challenging is understanding the processes that cause climate to change, and how big an effect a changing climate will have on the environments that we live in.

 

Mer de Glace, Chamonix, France
The Mer de Glace has retreated by >1 km since the late 19th century.

One way in which we can try to predict how big future climatic changes will be, and their effects is through investigating how climate has changed in the past – and this is a major theme of research for many environmental scientists. The Quaternary period is a time period that spans from 2.6 Ma to the present day, and is characterised by climatic transitions from ice-house to green-house temperatures. During the ice-house, or glacial periods, large ice-masses developed in the Northern hemisphere and in mountainous regions, which resulted in the development of large U-shaped valleys in areas such as Norway, Switzerland and even in Scotland where there are no glaciers present today. During the warm, or interglacial periods, the large ice-masses retreated as temperatures increased.

A sample of a Greenland ice-core is sampled for tephra analysis.
An ice-core is sampled for tephra analysis.

We know that temperatures changed between the glacial and interglacial periods from different proxy records, such as the oxygen-isotope record from the Greenland and Antarctic ice-cores. These records are invaluable because they have their own age-record (chronology) provided by counting the individual layers of ice, however, relating these temperature changes to the record of climate change preserved in the landscape is much more challenging and requires the use of different, specialised dating methods (for example tephrochrononlogy).

Radiocarbon dating is probably the most famous of the different Quaternary dating methods that are available, however this technique can only be used when organic material is available and can only date back to 50,000 years – which seems like a long time, but actually only covers ~3% of the Quaternary period. An alternative method is optically stimulated luminescence dating, which can be applied in a larger number of environments over a time period of between 10 and 500,000 years. All Quaternary dating methods have their advantages and disadvantages, and the most robust chronologies can be developed where multiple dating techniques are employed together. A selection of key Quaternary dating techniques are summarised here.

A rock hearth in the Libyan Sahara, which is a relic of human occupation. Photo credit: S. Armitage
A rock hearth in the Libyan Sahara, which is a relic of human occupation. Photo credit: S. Armitage

In addition to evidence from the landscape, early human populations were much more vulnerable to climatic changes than modern day populations. The patterns and timings of their migration can be used to understand regional changes in environments, as well as human evolution. This again help us to understand how environments change in response to changing climates and reconstructing these patterns also provides an insight into the evolution and development of modern societies, cultures and changes in land-use.

A site about different techniques for dating environmental changes