Spec S1

Question 1

Methods used to reconstruct past climates

Answer 1

Sea floor sediments
Ice cores
Lake sediments
Tree rings
Fossils

Question 2

Sea-floor sediments

Answer 2

• The fossil shells to tiny sea creates called foraminifera, which accumulate in sea-floor sediments, can be used to reconstruct past climates
• The chemical composition of foraminifera shells (ie. calcium carbonate) indicates the ocean temperatures in which they formed

Question 3

Ice cores

Answer 3

• Ice cores from the polar regions contain tiny bubbles of air - records of the gaseous composition of the atmosphere in the past
• Scientists can measure the relative frequency of hydrogen and oxygen atoms with stable isotopes
• The colder the climate the lower the frequency of these isotopes

Question 4

Lake sediments

Answer 4

• Past climates can be reconstructed from pollen grains, spores, diatoms and valves in lake sediments
• Pollen analysis identifies past vegetation types and from this infers palaeoclimatic conditions, pollen diagrams show the number of identified pollen types in the different sediment layers
• Diatoms are single-celled algae found in lakes with cell walls made of silica, they record evidence of past climates in their shells
• Varves are tiny layers of lak sediment comprising alternating light and dark bands, the light bands formed from coarser sediments indicate high energy, meltwater run-off in spring and summer, the darker bands, made up of fine sediment, show deposition during the winter months

Question 5

Tree rings

Answer 5

• The study of tree rings or dendrochronology is the dating of past events such as climate change through study of tree ring (annule) growth
• Annules vary in width each year depending on temperature conditions and moisture availability

Question 6

Fossils

Answer 6

• Plants and animals require specific environmental conditions to thrive, some such as coral reeds are highly sensitive to temperature, water depth and sunlight
• Where they exist in the fossil record, they can be used as proxies for climate, animals are more adaptable, however some herbivorous dinosaur species only survived in sub-tropical habitats

Question 7

What are greenhouse conditions?

Answer 7

• High atmospheric CO2
• High global temperatures
• High sea levels

Question 8

What are icehouse conditions?

Answer 8

• Low atmospheric CO2
• Low global temperatures
• Low sea levels as large part of continental surface covered by ice

Question 9

What are glacial and interglacial periods?

Answer 9

Glacial - colder periods
Interglacial - warmer periods
Operate on shorter timeframe during periods of icehouse conditions

Question 10

What were climatic conditions like 100 million years ago?

Answer 10

• Average global temperatures 6-8 degrees higher than present
• No polar ice-caps
• Sub-tropical conditions extending from Alaska to Antarctica

Question 11

What were the reasons behind these conditions?

Answer 11

• Atmospheric CO2 levels 5x higher than today
• Continental configuration affected ocean circulation and the Earth’s energy budget

Question 12

What were climatic conditions like 55 million years ago?

Answer 12

• Global temperatures peaked at 23 degrees
• Pangea in process of splitting into separate continents
• During this period globe warmed 5-9 degrees, most ecosystems were able to adapt as this happened slowly

Question 13

What were the reasons behind these conditions?

Answer 13

• Suspected that huge amounts of carbon were released into the atmosphere and oceans in the form of carbon dioxide and methane

Question 14

What were climatic conditions like 35 million years ago?

Answer 14

• Rapid transition to cooler conditions related to a major reeducation in atmospheric greenhouse gases (especially CO2)
• Glaciations of Antarctica during this period, largest glacial system on the plant, the entire continent is covered in an ice sheet, 25-30 x 10^6 km^3 of glacial ice
• The thickness is such that most mountain ranges are totally covered
• Fossil records show that continent previously experienced sub-tropical conditions, however 35 million years ago it rapidly descended into a permanent icehouse state

Question 15

What were the reasons for this glaciation?

Answer 15

• 35 million years ago, CO2 levels dropped rapidly from 1000-1200ppm to 600-700ppm
• Continental drift - Antarctica moved toward the South Pole, an ocean current known as the Antarctic Circumpolar Current then insulated the warmer water further north
• Submerged volcanic arc, known as the South Sandwich Islands disrupted deep-water ocean currents around Antarctica, this then isolated the continent from warmer waters of the South Pacific, Atlantic and Indian Oceans

Question 16

What were climatic conditions like during Quaternary glaciation?

Answer 16

• Spans the last 2.6 million years
• One of key characteristics is cyclical change of climate with long cold periods (glacial) and warmer periods (interglacial), glacial periods around 100,000, interglacial around 10,000-15,000 years
• There have been 4 major glacial episodes and 4 interglacials in the past 450,000 years
• Most recent glacial period known as Devensian, around 20,000 years ago - 1/3 of continental surface covered by ie
  -Scotland, ice sheets up to 1km deep, most of north England, West Midlands, Wales and Ireland was covered by ice sheets

Question 17

What are climatic conditions like during our present interglacial period?

Answer 17

• 90% of current Quaternary period consisted of glacial periods
• During Holocene, the only remaining continental ice sheets are Antarctica and Greenland
• Glacial remnants, such as glaciers and ice fields only exist in high latitude and high altitude areas in the present day
• 6000 years ago, temperature was 1-2 degrees higher
• 1100-1300, medieval warming period
• 1550-1850, ‘little ice age’, average temperature fell by 1 degree

Question 18

Factors associated with how natural forcing has driven climate change in the geological past

Answer 18

• Milankovitch cycles (orbital eccentricity, obliquity, precession of Earth’s axis)
• Volcanic eruptions
• Plate tectonics and continental drift
• Ocean circulation
• Natural greenhouse gases
• Solar output

Question 19

What are Milankovitch Cycles?

Answer 19

• Cyclical changes in the Earth’s circumnavigation of the sun which create alterations in the seasonality of solar radiation reaching the Earth’s surface
• These times of increased or decreased solar radiation directly influence the Earth’s climate system, impacting the advance and retreat of Earth’s glaciers
• There are three cycles which are collectively known as Milankovitch cycles: orbital eccentricity, obliquity and precession of the Earth’s axis

Question 20

What is orbital eccentricity?

Answer 20

• The Earth’s orbit around the sun follows an elliptical path with the eccentricity of the orbit varying from near circular to markedly elliptical over periodicities of 96,000 and 413,000 years
• These orbits change the distance the sun’s short wav radiation must travel to reach the Earth
• At maximum eccentricity, there is a 30% difference in solar radiation between when Earth is closest to the sun (perihelion) and where it is farthest (aphelion)
• Elliptical orbit results in global temperature decrease as the closeness to the sun during summer periods is not enough to counteract the longer, colder winter periods

Question 21

What is obliquity?

Answer 21

• Relates to the inclination of the Earth’s axis in relation to its orbit around the sun
• Varies over a period of 40,000 years from 22 to 24.5 degrees
• When the tilt is closer to 22 degrees, seasonal differences are reduced and it increases the difference in radiation received between equatorial and polar areas
• Snow and ice accumulating during the winter do not melt during the summer, which results in the growth of ice sheets, this has a positive feedback effect as it increases the albedo, more radiation reflected back and temperatures lowered further
• Tilt closer to 22 = poles receive much less energy = ice sheet growth = global temperature decrease = positive feedback

Question 22

What is precession of the Earth’s axis?

Answer 22

• Earth wobbles on its axis, which means that the point in earth’s orbit when the plane is closest to the sun (perihelion) varies over time
• This has a periodicity of 22,000 years and is linked to the gravitational influence of the Moon and Jupiter
• Changes in precession affect the intensity of seasons, if perihelion occurs during the northern hemisphere’s winter, winter will be warmer and summers cooler
• Snow and ice accumulating in winter will not melt completely next summer, therefore ice and snow cover expands continually, eventually triggering a glacial period

Question 23

How have Milankovitch cycles influenced the advance and retreat of Earth’s glaciers?

Answer 23

• These cycles help to explain the episodic nature of glacial and interglacial periods within the present ice age
• Where the cycles all reach their maximums, which have interglacial periods, however, where these cycles all reach their lowest, we have glacial periods (the Pleistocene ice age was the result of all three cycles operating together
• These cycles operate on timescales varying from 10,000 years to 100,000 years
• Milankovitch identified climate cycles at 100,000, 43,000 and 19,000 years with long glacial periods followed by short interglacials

Question 24

How have volcanic eruptions impacted Earth’s climate in the past?

Answer 24

• When volcanoes erupt, huge amounts of volcanic ash and sulphur dioxide are pumped i to the stratosphere by volcanic eruptions, leading to short term change in climate
• Sulphur dioxide has a cooling effect, it is converted to sulphuric acid, which forms sulphate aerosols, which reflect solar radiation back into space, lowering temperatures
• Longer term warming effect due to release of CO2

Question 25

How have plate tectonics and continental drift impacted Earth’s climate in the past?

Answer 25

• Driven by plate tectonics and sea-floor spreading, the global distribution and configuration of the continents have changed dramatically over geological time - 250 million years ago the continents formed a single, huge land mass, Pangea
• Tectonic changes on this scale have a direct impact on the global climate, eg. as a larger continental area occupies higher latitudes, the land area with permanent ice cover expands, this increases global albedo and positive feedback, which forces global cooling

Question 26

How has ocean circulation impacted Earth’s climate in the past?

Answer 26

• Ocean currents transfer surplus energy from tropics to poles
• 5 million years ago, when the North and South American continents joined and closed the ‘gateway’ between the Pacific and Atlantic, it intensified the Gulf Stream (carrying water from the Caribbean to the North Atlantic)
• Precipitation and evaporation increased and the prevailing westerly winds caused more precipitation in the North Atlantic, Europe and Siberia, diluting the salinity of the North Atlantic and Arctic oceans, this reduced salinity weakened the downwelling of water in the North Atlantic, which acts as a pump for the whole thermohaline circulation
• With less saline surface waters and a reduction in heat transferred by the gulf stream, this led to the expansion of sea ice in the North Atlantic and Arctic, this change was amplified by positive feedback effects with increased reflection of solar radiation, and the insulation of warmer ocean waters sealed beneath the sea ice
• This was the prelude to the onset of glaciation around 3 million years ago

Question 27

How have natural greenhouse gases impacted Earth’s climate in the past?

Answer 27

• Close relationship between atmospheric CO2 and average global temperatures
• Periods of icehouse earth corresponds to low levels of atmospheric CO2, reducing the natural greenhouse effect
• During the past 800,000 years, dominated by numerous glacial periods, CO2 levels have fluctuated between 170ppm and 300ppm (at present, 420ppm)
• Fifty million years ago, CO2 levels were 1000ppm, average temperatures were 10 degrees higher
• Atmospheric CO2 levels can be naturally reduced - as fold mountains such as the Himalayas, Andes and Rockies are formed, uplift of these mountains increased rainfall, erosion and chemical weathering
• Resulted in the removal of large volumes of CO2 which then became locked up in carbonate sediments in the oceans
• Increased nutrients in the oceans also led to the growth of phytoplankton, which extracted CO2 from the atmosphere for growth, when these died, the CO2 was trapped in deep ocean sediments

Question 28

How has solar output impacted Earth’s climate in the past?

Answer 28

• Solar output varies over time on timescales measured in millennia or centuries, these variations may be shown to contribute to climate change, however only amplify existing conditions, rather than being a sole attributer
• Sunspot activity can be used as a proxy for solar output, there is a positive correlation between sunspots and solar energy output
• Solar output follows an 11 year cycle, but the difference in energy output between the min and max sunspot activity is not enough to impact global climate significantly
• On longer timescales, solar output is more variable, near the end of the 17th century, sunspot activity declined to almost 0 for several decades, this corresponded to the severe winters in Europe known as the ‘little ice age’
• In the past 50 years, sunspot activity has been relatively high, coinciding with warming climate