x1.a The Earth’s climate is dynamic
What is climate change?
The large scale, long term change in the Earth’s weather pattern or average temperature
What is palaeoclimatology?
Study of past climates
Overview
★ Earth’s climate has undergone many changes in past 100 million years
★ Last 2.5 million years, quaternary period has witnessed changes in the earth's climate that
have been particularly fast
★ 20,000 years ago ice sheets covered most of NW europe
★ As global temperatures rise rapidly, ice sheets and glaciers shrink very quickly
Sea floor sediments
Foraminifera
★ Fossil shells of tiny sea creatures called foraminifera accumulate in sea floor sediments, can
be used to recreate past climates
How can they be used
★ Consist of shells of calcium carbonate and it is the chemical composition of these shells
which can tell us the sea level, temp + ocean conditions
★ Higher sea level means higher temperature
★ Go back 5 million years
Ice cores
Why are ice cores are useful climate proxies
★ Contains tiny bubbles of air trapped during the initial ice formation
★ Bubbles of air provide a record a gaseous composition of the atmosphere in the past
Which gases are measured
★ Relative frequency of hydrogen and oxygen atoms with stable isotopes can be measured
★ Can be used as a climate proxy as the lower frequency of isotopes the colder the climate
,Lake sediments
★ Pollen grains- pollen analysis can be used to show past vegetation types and in turn can be
used to infer palaeoclimatic conditions
Diatoms- what are they
How can we use them to reconstruct past climate?
★ Diatoms are microscopic plants found in lake sediments
★ Particularly useful for past climate studies due to sensitivity to different conditions
★ Shells are made from silica dioxide, helps them preserve well in fossil record
Varves
★ Thin layers of lake sediment made up of light and dark bonds
★ Light bands: coarser sediments from in spring and summer, high energy melt=water run off
★ Darker bands: fine sediments and show deposition in winter months
★ Thicker varves indicate warmer years
Tree rings (Dendrochronology)
★ Study of tree growth rings (annules) can enable us to date past events such as climate change
★ Each annule marks a year in the tree’s life and represents a complete cycle of seasons of
growth
★ They vary in width annually depending on the temperature and availability of moisture
★ Studying these rings and their width allows us to identity and date climate changes
Fossils
★ Plants and animals require specific environmental conditions
★ Some species are particularly sensitive to moisture and temperature fluctuations and where
these can be found in the fossil record they can therefore be used as proxies for climate
How can we use these to reconstruct climate
★ Highly sensitive to temperature, water depth and sunlight
★ Coral skeletons consists of calcium carbonate which is extracted from sea water
★ Contains oxygen isotopes, can be used to determine the temperature of the water in which
coral grew
Summary of fluctuations in the earths past climate
★ Greenhouse: high co2 levels, high global temperatures and high sea levels
★ Icehouse: low global temperatures and large part of the continental surfaces covered by ice
★ Within these periods there are glacial and interglacial periods which are on a very small
timescale
Examples of greenhouse conditions that occurred over 100 million years ago
★ Co2 atmospheric levels 5x higher than today
★ Sea levels were 100–200m higher.
★ Mid-cretaceous period (100 million years ago)
★ Average global temps were 6-8 degrees higher than now
★ No polar ice caps and subtropical conditions went from Alaska to Antarctica
,Paleocene
★ 55 million year ago
★ Spike in global temp, peaking at 23 degrees
★ Pangea was splitting into separate continents
★ Lasted for 200,000 years
★ Huge amounts of carbon released to atmosphere in form of co2 and methane
★ Globe warmed 5-9 degrees
★ Easier to adapt
When did the descent into permanent icehouse conditions occur for Antarctica?
★ 35 million years ago co2 levels dropped, rapidly from 1000-12000 ppm to 600-700 ppm
★ Continental drift, Antarctica moved towards the south pole away from south america +
Australia which isolated it
★ Ocean current (antarctic circumpolar) current insulated warmer water further north
★ Toward the south, submerged volcanic area known as south sandwich islands disrupted deep
water ocean currents around antarctica
★ Isolated continent from the warmer waters of the south pacifics, Atlantic and indian oceans
Glaciation of antarctica 35 million years ago
★ Antarctica is the largest glacial system on the planet and the whole continent is covered by a
huge ice sheet-
★ Thickness is such that only a few nunataks (mountain peaks) are exposed of the mountain
ranges that are under the ice
★ Despite its current conditions, evidence from the fossil record shows that the continents
experienced sub-tropical conditions
★ Around 35 million years ago that Antarctica descended into a permanent icehouse state
What is the term for a brief cold spell
★ Stadial
★ Most recent: Lomond or younger dryas, lasted roughly 1000 years
How much of the current Quaternary period has consisted of glacial periods
★ 90%
When did the holocene begin
★ began at the end of the last glacial (11,700 years ago) is an interglacial period.
★ warming temperatures, ice sheets and glaciers have shrunk and sea levels have risen over
100m.
★ only remaining continental ice sheets are Antarctica and Greenland.
★ Glacial remnants, such as glaciers and icefields only exist in high latitude and high altitude
areas in the present day.
, What happened between 1100-1300 and 1550-1850
★ 6,000 years ago - temps 1-2 degrees higher
★ 1100 – 1300 – Mediaeval Warm Period
★ 1550 – 1850 – ‘Little Ice-Age’ – average temperatures fell by 1°C and winters in Europe were
sent into a deep freeze.
What is the third epoch of the quaternary period
★ Humans have caused lots of climate change over last 200 years
★ Many scientists believe that as humans have influenced the climate so much it should be
called anthropocene
How has natural forcing driven climate change in the geological past
Milankovitch cycles - external
★ Orbital eccentricity
★ Obliquity (tilt of earth's axis)
★ Precession (wobble) of earth's axis
Changes in the Earth’s circumnavigation of the sun create alterations in the seasonality of solar
radiation reaching the earth's surface and these times of increased or decreased solar radiation directly
influences the earth's system, impacting retreat and advance of the earth's glaciers.
Orbital eccentricity- EXTERNAL
★ 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.
★ This changes the distance the sun’s short wave radiation must travel to the earth.
★ At maximum eccentricity 30% difference in solar radiation between when earth is closest to
the sun (perihelion) and when earth is further from the sun (aphelion).
★ Ice ages occur when it is at maximum orbital eccentricity
Obliquity- EXTERNAL
★ relates to the inclination of the earth’s axis in relation to its orbit around the sun
★ This 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 – results in the
growth of ice sheets.
★ This has a positive feedback – as increases the albedo – more radiation reflected back and
temperatures lower further.
Precession- EXTERNAL
★ Earth ‘wobbles’ on its axis like a giant spinning top which means that the point in the earth’s
orbit when the planet is closest to the sun (perihelion) varies over time.
★ This ‘wobble’ has a periodicity of 22,000 years and is linked to the gravitational influence of
the Moon and Jupiter.
★ Changes in the precession that affect the intensity of seasons.
What is climate change?
The large scale, long term change in the Earth’s weather pattern or average temperature
What is palaeoclimatology?
Study of past climates
Overview
★ Earth’s climate has undergone many changes in past 100 million years
★ Last 2.5 million years, quaternary period has witnessed changes in the earth's climate that
have been particularly fast
★ 20,000 years ago ice sheets covered most of NW europe
★ As global temperatures rise rapidly, ice sheets and glaciers shrink very quickly
Sea floor sediments
Foraminifera
★ Fossil shells of tiny sea creatures called foraminifera accumulate in sea floor sediments, can
be used to recreate past climates
How can they be used
★ Consist of shells of calcium carbonate and it is the chemical composition of these shells
which can tell us the sea level, temp + ocean conditions
★ Higher sea level means higher temperature
★ Go back 5 million years
Ice cores
Why are ice cores are useful climate proxies
★ Contains tiny bubbles of air trapped during the initial ice formation
★ Bubbles of air provide a record a gaseous composition of the atmosphere in the past
Which gases are measured
★ Relative frequency of hydrogen and oxygen atoms with stable isotopes can be measured
★ Can be used as a climate proxy as the lower frequency of isotopes the colder the climate
,Lake sediments
★ Pollen grains- pollen analysis can be used to show past vegetation types and in turn can be
used to infer palaeoclimatic conditions
Diatoms- what are they
How can we use them to reconstruct past climate?
★ Diatoms are microscopic plants found in lake sediments
★ Particularly useful for past climate studies due to sensitivity to different conditions
★ Shells are made from silica dioxide, helps them preserve well in fossil record
Varves
★ Thin layers of lake sediment made up of light and dark bonds
★ Light bands: coarser sediments from in spring and summer, high energy melt=water run off
★ Darker bands: fine sediments and show deposition in winter months
★ Thicker varves indicate warmer years
Tree rings (Dendrochronology)
★ Study of tree growth rings (annules) can enable us to date past events such as climate change
★ Each annule marks a year in the tree’s life and represents a complete cycle of seasons of
growth
★ They vary in width annually depending on the temperature and availability of moisture
★ Studying these rings and their width allows us to identity and date climate changes
Fossils
★ Plants and animals require specific environmental conditions
★ Some species are particularly sensitive to moisture and temperature fluctuations and where
these can be found in the fossil record they can therefore be used as proxies for climate
How can we use these to reconstruct climate
★ Highly sensitive to temperature, water depth and sunlight
★ Coral skeletons consists of calcium carbonate which is extracted from sea water
★ Contains oxygen isotopes, can be used to determine the temperature of the water in which
coral grew
Summary of fluctuations in the earths past climate
★ Greenhouse: high co2 levels, high global temperatures and high sea levels
★ Icehouse: low global temperatures and large part of the continental surfaces covered by ice
★ Within these periods there are glacial and interglacial periods which are on a very small
timescale
Examples of greenhouse conditions that occurred over 100 million years ago
★ Co2 atmospheric levels 5x higher than today
★ Sea levels were 100–200m higher.
★ Mid-cretaceous period (100 million years ago)
★ Average global temps were 6-8 degrees higher than now
★ No polar ice caps and subtropical conditions went from Alaska to Antarctica
,Paleocene
★ 55 million year ago
★ Spike in global temp, peaking at 23 degrees
★ Pangea was splitting into separate continents
★ Lasted for 200,000 years
★ Huge amounts of carbon released to atmosphere in form of co2 and methane
★ Globe warmed 5-9 degrees
★ Easier to adapt
When did the descent into permanent icehouse conditions occur for Antarctica?
★ 35 million years ago co2 levels dropped, rapidly from 1000-12000 ppm to 600-700 ppm
★ Continental drift, Antarctica moved towards the south pole away from south america +
Australia which isolated it
★ Ocean current (antarctic circumpolar) current insulated warmer water further north
★ Toward the south, submerged volcanic area known as south sandwich islands disrupted deep
water ocean currents around antarctica
★ Isolated continent from the warmer waters of the south pacifics, Atlantic and indian oceans
Glaciation of antarctica 35 million years ago
★ Antarctica is the largest glacial system on the planet and the whole continent is covered by a
huge ice sheet-
★ Thickness is such that only a few nunataks (mountain peaks) are exposed of the mountain
ranges that are under the ice
★ Despite its current conditions, evidence from the fossil record shows that the continents
experienced sub-tropical conditions
★ Around 35 million years ago that Antarctica descended into a permanent icehouse state
What is the term for a brief cold spell
★ Stadial
★ Most recent: Lomond or younger dryas, lasted roughly 1000 years
How much of the current Quaternary period has consisted of glacial periods
★ 90%
When did the holocene begin
★ began at the end of the last glacial (11,700 years ago) is an interglacial period.
★ warming temperatures, ice sheets and glaciers have shrunk and sea levels have risen over
100m.
★ only remaining continental ice sheets are Antarctica and Greenland.
★ Glacial remnants, such as glaciers and icefields only exist in high latitude and high altitude
areas in the present day.
, What happened between 1100-1300 and 1550-1850
★ 6,000 years ago - temps 1-2 degrees higher
★ 1100 – 1300 – Mediaeval Warm Period
★ 1550 – 1850 – ‘Little Ice-Age’ – average temperatures fell by 1°C and winters in Europe were
sent into a deep freeze.
What is the third epoch of the quaternary period
★ Humans have caused lots of climate change over last 200 years
★ Many scientists believe that as humans have influenced the climate so much it should be
called anthropocene
How has natural forcing driven climate change in the geological past
Milankovitch cycles - external
★ Orbital eccentricity
★ Obliquity (tilt of earth's axis)
★ Precession (wobble) of earth's axis
Changes in the Earth’s circumnavigation of the sun create alterations in the seasonality of solar
radiation reaching the earth's surface and these times of increased or decreased solar radiation directly
influences the earth's system, impacting retreat and advance of the earth's glaciers.
Orbital eccentricity- EXTERNAL
★ 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.
★ This changes the distance the sun’s short wave radiation must travel to the earth.
★ At maximum eccentricity 30% difference in solar radiation between when earth is closest to
the sun (perihelion) and when earth is further from the sun (aphelion).
★ Ice ages occur when it is at maximum orbital eccentricity
Obliquity- EXTERNAL
★ relates to the inclination of the earth’s axis in relation to its orbit around the sun
★ This 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 – results in the
growth of ice sheets.
★ This has a positive feedback – as increases the albedo – more radiation reflected back and
temperatures lower further.
Precession- EXTERNAL
★ Earth ‘wobbles’ on its axis like a giant spinning top which means that the point in the earth’s
orbit when the planet is closest to the sun (perihelion) varies over time.
★ This ‘wobble’ has a periodicity of 22,000 years and is linked to the gravitational influence of
the Moon and Jupiter.
★ Changes in the precession that affect the intensity of seasons.
