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Question 1

Quaternary period

Answer 1

We are currently living in the Quaternary, which began around 2 million years ago as the Tertiary period ended with the onset of global cooling and ice-house conditions.

Recent theories suggest that plate tectonics created suitable conditions to ‘kick start’ the Pleistocene by positioning Antarctica as an isolated continent at the South Pole.

the Quaternary Ice Age is just the latest of several ice ages over geological time.

Question 2

the Quaternary period is divided into two epochs of geological time:

Answer 2

• The Pleistocene covers the time span from the beginning of the Quaternary to about 11,500 years ago when the most recent continental glacial (UK Devensian) ended.
• The Holocene interglacial (the period we now live in) is similar climatically to previous interglacials, but is distinctive as it is noted for the growth of human civilisation, the development of agriculture and industrialisation.

Question 3

Glacials:

Answer 3

Cold, ice-house periods within the Pleistocene.

Question 4

Interglacials:

Answer 4

Warmer periods similar to the present, i.e. greenhouse periods.

Question 5

Ice-house conditions:

Answer 5

Very cold glacial conditions.

Question 6

Greenhouse conditions:

Answer 6

Much warmer interglacial conditions.

Question 7

Pleistocene:

Answer 7

A geological period from about 2 million years ago to 11,700 years ago, the early part of the quaternary which included the most recent ice age.

Question 8

Stadials and interstadials:

Answer 8

Short-term fluctuations within ice-house-greenhouse conditions; stadials are colder periods that lead to ice re-advances.

Question 9

Causes of longer-term glacial/ interglacial cycles

Answer 9

Long-term changes in the Earth’s orbit around the Sun are currently seen as the primary cause of the oscillations between glacial and interglacial conditions.
The Milankovitch theory based on orbital/astronomic forcing of glacial periods takes into account three main characteristics of the Earth’s orbit

Question 10

Eccentricity

Answer 10

earth orbit changes from being more elliptical to more circular and back again over a period of around 100,000 years, so changing the amount of radiation received from the Sun (this is considered the dominant factor).

Question 11

Axial tilt

Answer 11

varies from 21.8° to 24.4° (currently the tilt is 23.5°) over a timescale of around 41,000 years.
This changes the intensity of sunlight received at the poles and, therefore, the seasonality of the Earth’s climate. The greater the tilt, the greater the difference between summer and winter.

Question 12

Wobble

Answer 12

the Earth wobbles on its axis (just like a spinning top) changing the point in the year at which the Earth is closest to the Sun (axial precession) over a 21,000 year time cycle. This causes long-term changes to when different seasons occur along the Earth’s orbital path.

Question 13

Milankavitch cycles overall

Answer 13

The three orbital cycles can combine together to minimise the amount of solar energy reaching the Northern hemisphere during summer (leading to cooler summers overall).

In support of Milankovitch’s theory is the fact that glacials seem to have occurred at regular intervals of approximately 100,000 years.

However the actual impact of the combined orbital changes on solar radiation amount and distribution is small, probably only enough to change global temperatures by between 0.5 °C and 1 °C.

To explain the larger temperature changes of up to 5 °C that were required for the vast expanses of ice to form, or alternatively melt, we have to look at climate feedback mechanisms.

In conclusion, many scientists see Milankovitch cycles as a possible trigger for major ice-house-greenhouse changes, or even as a good ‘pacemaker’ during each cycle.

It is the climate feedback mechanisms, however, which sustain the drive towards either colder or warmer conditions and which led to the glacial and interglacial periods.

Question 14

Diagram Milankovitch cycles

Answer 14

Question 15

Orbital/astronomic forcing:

Answer 15

A mechanism that alters the global energy balance and forces the climate to change in response.

Question 16

Feedback cycles

Answer 16

Feedback effects are those that can either amplify a small change and make it larger (positive feedback) or diminish the change and make it smaller (negative feedback).

A number of interacting Earth systems are involved, as shown in Table 4.1 below.

Question 17

Positive feedback:

Answer 17

increasing the cooling rates:
* Snow and ice cover.
Small increases in snow/ice raise surface albedo (reflectivity) so more solar energy is reflected back into space, leading to further cooling, which could lead to further snowfall and ice cover.

increasing the warming rates:
The melting of snow/ice cover by carbon dioxide emissions decreases albedo; methane is emitted as permafrost melts, and warming seas lead to calving of ice sheets, which all lead to loss of snow/ice cover and of surface albedo, decreasing reflectivity and accelerating further warming.

Question 18

Negative feedback:

Answer 18

decreasing the warming or cooling rates
Increasing global warming leads to more evaporation and, over time, pollution from industrialisation adds to global cloud cover.

Increasingly cloudy skies could reflect more solar energy back to space and diminish the effect of warming - so called ‘global warming’ may be less intense because of this global dimming.

Ice sheet dynamics can disrupt the thermohaline circulation (THC).

Warming water in the Arctic disrupts ocean currents; less warm water from the Gulf Stream is drawn north, which could lead to global cooling in northern Europe.

Question 19

Albedo:

Answer 19

The reflective coefficient of a surface, i.e. the proportion of incident radiation reflected by a surface (very high in the case of snow or ice).

Question 20

Calving:

Answer 20

The breaking up of chunks of ice at the glacier snout or ice sheet front to form icebergs as the glacier reaches a lake or the ocean.

Question 21

Thermohaline circulation:

Answer 21

A global system of surface and deep-water ocean currents driven by differences in temperature (thermo) and salinity (haline) between areas of the oceans. Sometimes known as the ocean conveyor.

Question 22

Possible explanations for shorter-term fluctuations

Answer 22

solar forcing/ sunspots

volcanic eruptions

Question 23

Solar forcing

Answer 23

• The amount of energy emitted by the Sun varies as a result of the number and density of sunspots (dark spots on the Sun’s surface caused by intense magnetic storms).
• There are a number of cycles of varying length including the ‘eleven-year sunspot cycle’.
• A longer period with no sunspot activity, known as the Maunder Minimum, occurred between 1645 and 1715, at the height of the Little Ice Age, to which it has often been linked, whereas the preceding medieval warm period has been linked to more intense sunspot activity.
• The big problem is that total variation in solar radiation caused by sunspot activity is only 0.1 per cent and is not by itself enough to explain the climate fluctuations.
• Even so, some scientists suggest that around twenty per cent of twentieth-century warming may be attributed to solar output variation.

Question 24

Volcanic causes

Answer 24

• Eruptions with a high volcanic explosivity index (VEI) eject huge volumes of ash, sulphur dioxide, water vapour and carbon dioxide into the atmosphere (volcanic aerosols), which high-level winds distribute around the globe.
• have impacts for around 10 years
• e.g Philippines eruption in 1991 lowered global temperatures by 0.5 C from 1991 to 1993

Question 25

Loch Lomond Stadial (the Younger
Dryas event)

Answer 25

• around 12,500 years ago the temperatures plunged downwards and, by 11,500 years ago, glacial conditions occurred with temperatures 6-7 °C lower.
• Glaciers re-advanced in many parts of the world including the formation of ice caps in the Scottish Highlands, from which cirque and valley glaciers flowed outwards, with smaller areas of cirque glaciers in the Lake District and North Wales.
• Greenland ice core data suggested a very rapid temperature rise of 7 °C after the event (perhaps in only 50 years) with a corresponding rapid rise in sea level.
• The timing would seem to be inconsistent with orbital forcing, as neither solar forcing nor volcanic eruptions could lead to a fluctuation of such magnitude.
• One possibility was that the Loch Lomond Stadial was triggered when drainage of the huge proglacial Lake Agassiz disrupted the
  THC, thus cutting off the poleward heat transport from the Gulf Stream.

Question 26

The Little Ice Age - the longest glacial oscillation in historical times

Answer 26

• Between 1550 and 1750 there was a low trough of very cold conditions, known as the Little Ice Age, which occurred globally.

There were many impacts:
* The widespread abandonment of upland farms in Scandinavia and Iceland.
* Many glaciers in Europe re-advanced down valleys; the Little Ice Age was a period of predominantly positive net mass balance leaving prominent terminal moraines from which the glaciers subsequently retreated, but often at different dates/ times around the world.
* Arctic Sea ice spread further south with polar bears seen frequently in Iceland.
* Rivers in the UK and lowland Europe, and New York harbour, froze over.
* Curling developed as a national sport in Scotland as there were so many frozen lakes and rivers.

• Some researchers argue that the Little Ice Age could have developed into a new stadial but that this was prevented by the onset of the Industrial Revolution, fired by coal.
• The release of carbon dioxide triggered climate warming, which dramatically halted the cold period.