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Evidence for Climate Change
 What are four sources of evidence for climate change?
 ___________________
___________________
 ___________________
Ice Cores
 Limitations with thermometer S___________ t_____________ readings:
 __________________________________
 __________________________________
 Peat Bogs – What is a peat bog?
 How can studying peat bogs help us find out about the climate?
 Why are pollen grains useful for finding out about past climates?
Evidence for Climate Change
 The lighter rings are new _________ __________ produced in
_________.
 Most growth during this time, hence the wider xylem
diameter.
 Darker rings are produced in the ___________, smaller more
dense __________ tissue is produced.
 In Autumn and winter little, if any, growth occurs
 What can the tree rings tell us about the tree?
 What to assume when reading a core sample:
Putting the Data Together
 Human temperature readings: now - ________
 Tree ring studies: now - ____BC (hundreds to 3000 yrs ago)
 Pollen in peat bogs: now– ___________BC (20 000 yrs ago)
 Ice cores: now – further than _______________yrs ago
Topic 5.3, Evidence for Climate
Change
Evidence for Climate Change
 Read page 31
 What are three sources of evidence for climate change?
 Temperature records
 Pollen in peat bogs
 Dendrochronology
 Activity 5.9 Long term temperature changes
 Some of the limitations with thermometer surface
temperature readings:
 Only go back a few centuries
 May only be in one area, country, altitude and latitude
Peat Bogs
 We can use peat bogs to study plant and animal material
that indicate the climate up to about 12 000 years ago
 What is a peat bog?
 Wetland that accumulates peat
 What is peat?
 Peat is partially decayed plant (often mosses) and
animal matter.
 The water is acidic.
Peat Bog
Peat Bogs
 Why is peat created rather than complete decay?
 Waterlogged conditions (anaerobic) and acidic
conditions slow down decay.
 Not as much oxygen, more anaerobic respiration, less
energy for microorganisms to reproduce, survive and
decompose.
 Acidic conditions may affect enzyme activity, slows
decay.
Peat Bogs
Peat bog being harvested for fuel
Tollund man found in peat bog in
Denmark – 2000 years old
Studying peat bogs helps us learn
about the climate
 Read p32 and answer the following 2 questions
 How can studying peat bogs help us find out about the climate?
 Why are pollen grains useful for finding out about past climates?
Studying peat bogs helps us learn
about the climate
 How can studying peat bogs help us find out about the climate?
 Study the pollen grains – tell us about the climate
 Peat forms in layers, deeper the layer, the older the peat. Carbon-14
dating allows us to date the pollen.
Studying peat bogs helps us learn
about the climate
 Why are pollen grains useful for
finding out about past climates?
 Huge amount of pollen produced
 Tough outer layer – resistant to
decay
 Identify plant species by pollen
grain (each plant, different type)
 Each plant has a certain set of
ecological conditions in which it
grows best. If lot of pollen found
from plant favouring warm
conditions (cactus or succulent)
then we can infer that the climate
was warm when peat layer was
formed
Radiocarbon dating
 All plants and animals on Earth are made principally of
carbon
 A tiny part of the carbon on the Earth is radioactive
Carbon-14 (C14), or radiocarbon.
 This is unstable and decays, releasing particles
 We know how quickly this decay happens and can measure
this in half life
 Half life of C-14 is 5568 years.
 By measuring the amount of C-14 left in a sample we can
work out how old it is
Pollen in Peat Bogs
 Activity 5.10 – Pollen core activity using
worksheets.
 Note that pollen is only produced when trees reach
sexual maturity. To do so, the conditions have to be
favourable
Activity 5.10 Pollen Analysis
Plants found
in each
zone:
Vegetation:
Light:
1 Mountain avens
Purple saxifrage
2 Birch
Great reedmace
3 Scots pine
Birch
4 Hazel
Common oak
Beech
1 Absence of stable
vegetation. Only
hardy arctic – alpine
plants can survive.
2 Establishment of
dwarf shrubs and
water plants.
3 Establishment of
pioneer foresttrees.
4 Vigorous growth of
mature forests.
1 Lack of tree cover
allows shadeintolerant plants
to establish.
2 Lack of tree cover
allows shadeintolerant plants to
establish.
3 In the early stages of
tree growth there is little
shade, allowing shadeintolerant trees to grow.
4 Dense growth
provides cover
which suppresses
shade-intolerant
plants.
3 A warming climate
allows a sufficient
time period each year
when the soil is not
frozen. Organic matter
can start to build up in
the soil.
4 As warmer, stable
conditions prevail
for a large proportion
of the year, mature,
fertile soils develop.
.
Climate:
1 While large parts of
the year are dominated
by extreme cold, the
frozen arctic–alpine soil
that exists has little or
no organic material
present, and there are
patches of bare rock.
2 As rising
temperatures allow
some thawing of ice
sheets, the soil left
behind has little or no
organic material.
Activity 5.10 Pollen Analysis
Q3 Hazel did not appear before 10 000 years ago due to the
climate being too cold. Hazel also requires mature fertile soils
that develop in warmer climates. After 5000 years ago, the
dense forest cover favoured other trees rather than hazel.
Warming of the climate is suggested between 15 000 and
10 000 years ago.
Tree-ring analysis –
dendrochronology
 Questions 5.26 and
5.27 on p33 in text
book
 Complete page 1 of
Activity 5.11a
Tree-ring analysis –
dendrochronology
 Function of
 Xylem vessels: water and mineral transport and
structural support
 Phloem sieve tubes: transport sugars from
photosynthesis (sucrose) & hormones
 Cambium: Cell layer that produces new xylem & phloem
cells
 Sclerenchyma fibres: Stiffened cell walls – support
Tree-ring analysis –
dendrochronology
 Structure of
 Xylem
 Form a continuous colum to act as a tube for water
 End walls are lost or perforated
 Thick lignified walls – support & waterproofing
 Dead – autolysis
 Pits in walls to allow water movement between vessels
 Sclerenchyma
 Hollow – but do not form continuous column for transport of water
 Thick lignified walls – support
 Dead – autolysis
 Chisel-shaped ends
Tree Rings
 There are light & dark rings
found in a tree.
 The lighter rings are new xylem
vessels produced in spring.
 Most growth during this time,
hence the wider xylem diameter.
 Darker rings are produced in the
summer, smaller more dense
xylem tissue is produced.
 In Autumn and winter little, if
any, growth occurs
Tree Rings
 What can the tree rings tell us
about the tree?
 Age of the tree
 Width of the lighter rings show us
how favourable the climate was in
Spring
 The wider the lighter rings, the
more favourable the conditions for
growth were – warm, wet, mineral
rich soils
 Do you have to cut the tree down
to count the rings?
 No, core samples can be taken.
Tree Rings
 What to assume when reading a core
sample:
 That the dark and light rings are produced
annually.
 The tree’s growth requirements are the
same throughout its life.
 Only a limited number of factors affect the
widths of rings.




Complete page 2 of Activity 5.11a
Interactive 5.11 Activity from SNABonline
Complete Activity 5.11 Dendrochronology
Q 5.29
Putting the data together
 Read pages 35-36




Human temperature readings: now - 1650
Tree ring studies: now - 1500 BC (hundreds to 3000 yrs)
Pollen in peat bogs: now– 18 000BC (20 000 yrs ago)
Ice cores: now – further than 20 000 yrs ago
Ice Core Samples
 An ice core is a core sample which contains trapped
air bubbles from previous time periods.
 The ratio of different oxygen istopes in the trapped air
can give an estimate of the air temperature
 The air bubbles trapped in the ice cores allow for
measurement of gas concentrations including
greenhouse gases carbon dioxide, methane, and nitrous
oxide.
 They can also gives us clues about other factors, like ash
or pollutants in the atmosphere
 Look at graphs on page 36