Pleistocene Climate Change

What is the Pleistocene Epoch?

The Pleistocene Epoch is the first epoch of the Quaternary Period. It came immediately before the current Holocene Epoch.

The Pleistocene Epoch is known as the Ice Age due to its numerous glacial-interglacial cycles. The last glacial maximum was the Devensian, which occurred approximately 18,000 years ago.

The highlighted series in the table below explains the Pleistocene Epoch in the context of time period classifications.

The last period of glacial advance is known as the Loch Lomond Stadial. This occurred between 12,000 and 18,000 years ago, marking the end of the Pleistocene Epoch.

The Pleistocene Epoch is arguably the most influential compared to other ice ages as it has been the most instrumental in shaping the current topography of the world’s landscapes. This is due to temperature fluctuations taking place over approximately two million years.

Climate change characteristics of the Pleistocene Epoch

Some of the most important climate change characteristics of the Pleistocene Epoch include:

• Significant temperature fluctuations over two million years (approximate time of the Pleistocene Epoch) and subsequent multiple glacial-interglacial cycles.
• The ice extent at each glacial was different.
• Fluctuations within each major glacial, which included: relatively short-lived pulses of ice advance known as stadials, and warmer periods of glacial retreat known as interstadials.

The earth’s geological state over time

Current geological evidence suggests that the earth is around 4.6 billion years old. Throughout its history, the earth has been fluctuating between two dominant states known as the ‘Greenhouse Earth’ and the ‘Icehouse Earth’ – the result of various changes in the global climate.

Within the Icehouse and Greenhouse Earth classes, it is important to identify periods where glaciers advance (increase in size due to cooling factors) or retreat (decrease in size largely due to warming factors). Periods of glacial advance are known as glacials, whereas periods of glacial retreat are known as interglacials.

These variations are due to long- and short-term variations in the global climate. See our explanation on the Causes of Climate Change for more info!

Glacial classification

Era, period, and epoch classify the time scale of glacial periods. This is shown below:

Eras

Eras are the second-longest measures of geological time (second to aeons). Significant events in the earth’s history, like mass extinction events, separate eras. The Cenozoic Era (our current era) is separated from the Mesozoic Era (the era before) by a major extinction event caused by an asteroid impact 66 million years ago.

Periods

Periods are further subdivisions of geological time. These are usually defined by the times when specific systems of rocks were formed. We are currently in the Quaternary Period, which is characterised by many glacial advances and retreat cycles.

Epochs

Epochs are further divisions of geological times and are subdivisions of periods. Significant changes in rock layers separate epochs. Our current epoch is the Holocene, which began approximately 11,500 years ago after the last glacial period - the Pleistocene Epoch.

What started our current epoch was the Pleistocene megafaunal extinction event in which many mammals became extinct (sabre-toothed cats, giant ground sloths, mammoths, and giant armadillos). Note that these are all large mammals (the primary victims of the Pleistocene extinction).

How are glaciers and climate change related?

Glaciers and climate change impact one another and are closely related in terms of their behaviour. A critical piece of evidence for global warming is the increased rates of glacial retreat/decreased mass balances of glaciers.

Globally, the Glacier Mass Balance of ice sheets is decreasing, which shows increased ablation due to increased global temperatures.

Glaciers are also related to many feedback loops associated with climate change. One example is the Increased Albedo Feedback Loop, where increased surface ice increases the albedo effect. Consequently, a greater amount of solar radiation is reflected rather than absorbed by the earth’s surface, causing a decrease in overall temperatures. This then causes increased levels of surface ice through an increase in accumulative processes, repeating the cycle.

Conversely, the opposite feedback loop may also take place:

Increase in surface temperatures -> increased ablation and less surface ice-> reduced albedo effect -> less reflection of solar radiation -> increase in surface temperatures.

Climate change and the Pleistocene Epoch

One of the most significant examples of the relation between climate change and glaciation is the Pleistocene Epoch.

During this time, significant temperature fluctuations caused glacial/interglacial cycles over about two million years. Within each glacial cycle, there were further cycles of stadials and interstadials. The ice extent during the Pleistocene Epoch was significantly larger in high latitude areas, such as the Arctic Basin, Alaska, and other North American Basins.

The root of the fluctuations in ice extent within the Pleistocene Epoch was a combination of long-term causes of climate change, such as the Milankovitch cycles and tectonics, and short-term causes of climate change as ENSO cycles or solar output variation.

Variation in ice sheet distribution between the Pleistocene Epoch and current time

At the height of the Pleistocene ice extent, the ice cover was three times higher than present-day volumes. The two dominant ice sheets of our present day were only marginally greater at the height of the Pleistocene. The most significant differences were higher glacial volumes at high altitudes and high latitudes. The most notable changes were in the North American Basin, which includes the Arctic ice sheet, Alaska, and other North American ice covers.

Evidence of the Pleistocene Epoch in the UK

The evidence of the Pleistocene Epoch in the UK consists of glacial landforms formed during the ice age. This evidence is made up of three different categories of glacial landforms: depositional, erosional, and meltwater.

Depositional evidence

Here are two examples of depositional evidence.

Drumlins

These are large mound-like structures that directly show glacial deposition. They can be used to reconstruct former ice mass extent and movement using methods such as till fabric analysis or identifying stoss and lee slopes. They can be found in the Lake District, e.g. Vale of Eden in Cumbria, and other areas with significant ice masses during the Ice Age.

Drumlins are depositional glacial landforms

Erratics

These are boulder-like bodies of sediment not commonly found in the surrounding area. This indicates that they were carried from an area containing the material by a glacier and dropped off when the ice melted. These can also be found in the Lake District, e.g. the Bowder Stone.

Erosional Evidence

Evidence of erosion includes glacial features such as corries, arêtes, glacial troughs, roches moutonêes, crags, tails, and loch and lochan landscapes. Evidence is found in the Cairngorms (Scotland), Snowdonia (Wales), and the Lake District (England).

Glacial erosion evidence

Meltwater Evidence

Meltwater channels and glacial till (which can be analysed via till fabric analysis) can be found in Newtondale in North Yorkshire.

Lake District, UK. pixabay