Transcript Earths Climate History How do we know what we know

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Earth’s Climate History: How do we
know what we know? What DO we
know? Why does past climate matter
to us today?
Presented by: Carole Mandryk and Dr. Russanne
Low
September 20, 2011
Earth’s Climate History:
How do we know what we know?
Presented by: Dr. Russanne Low and Dr. Carole Mandryk
Overview
• How do we know what we know?
• What DO we know?
• Why does past climate matter to us today?
Presenters:
Russanne Low, Asst. Professor, School of
Natural Resources, University of Nebraska,
Lincoln; Senior Scientist, Institute for Global
Environmental Strategies Arlington, VA
Carole Mandryk, Research Fellow, Center
for Climate Change Communication,
George Mason University
[email protected]
[email protected]
Who are your students?
A.
B.
C.
D.
E.
Elementary
Middle/High School
College Level
Informal
Other
Why does past climate matter today?
In order to truly understand what is happening, or will
happen now, we must be able to answer the question:
“Is the Current Climate Change Unusual
Compared to Earlier Changes
in Earth’s History?”
(2007 IPCC FAQ 6.2)
How many of you have heard someone who questions
whether the current climate changes are caused primarily
by human activities and claim, “Climate changes all the
time”?
Why does past climate matter today?
They are right.
Earth’s climate does change all the time
– on many different time scales.
But because they don’t understand HOW – and equally
important – WHY – Earth’s climate has changed in the
past they miss the crucial point…
Why does past climate matter today?
Climate scientists know the changes of the last
150 years are NOT just nature changing all the
time because they know what those past climate
changes have been.
They know that the answer to the question,
“Is the current Climate Change Unusual
Compared to Earlier Changes in Earth’s
History?” is a resounding
Why does past climate matter today?
Yes!
By the end of today’s presentation you will be able to
explain why this is true to your students, too!
The focus of today’s webinar:
How do we know what we know?
Reconstructing Past Climates
1) Why climate changes
• (Climate system)
2) Where we find our evidence
• (data sources)
3) How we get our data and what do
they mean?
• (data discovery,
modeling &
interpretation)
1) When: How we know when climate
changed?
• (chronologies)
2) Telling the story
• (synthesis)
Let’s pause for questions
from the audience
Climate Change Throughout Earth History
There is only one thing that can change the
Earth’s Climate!
?
Climate Change Throughout Earth History
There is only one thing that can change the
Earth’s Climate!
Change in the Earth’s Energy Budget!
Climate Change Throughout Earth History
Take home message: Climate change is change in
Earth’s Energy Balance!
when
/ Outputs
Inputs ==
Earth’s energy budget is not in balance
Inputs > Outputs = Warming
Inputs < Outputs = Cooling
Different processes change EB at
different timescales
Changes in Earth Energy
Balance across different Time
scales
• Earliest Earth origins
• 1,000,000,000—
10,000,000
• 1,000,000-10,000
• 100
Influences operating at timescale
• cooling and consolidation
of crust evolution of
biosphere atmosphere
• tectonics, mountain
building and weathering
• changes in the Earth-Sun
geometry (orbital forcing)
• Solar variability, sunspots,
volcanism
CO2 Levels and Earth’s Temperature
The rate of increase of CO2 over the post industrial period is far more rapid
than any increases over the ice core record. Scientists say that the rate of
increase of carbon dioxide is presently over 10,000 times as fast as any
increase in the past. How do we know this?
Where do we find our evidence?
Not in a lab, doing controlled and reproducable experiments, like we were taught!
The Earth system is running our
experiments!
Natural History Experiments
in the Earth’s Climate Archives
Alluvial
Sediments Ice
Where we find our
evidence:
Glacial Sediments
Peat
Where we find our evidence: Sediments
Glacial Sediments
Eolian Sediments
Alluvial Sediments
Peat
Story inside the Sediments
Find an archive where climate information is stored in an organized way,
so that we know the sequence of events!
Hypothetical Lake Bottom: yearly accumulation of sediments
Just where is the climate data that tells
us how many degrees cooler it was?
varves,
rhythmites
distortion
Proxy Data
• Something in the
sediments, perhaps has
left fossil evidence of an
organism’s response to
past temperature?
• Perhaps the sediments
themselves contain
minerals that form only
under specific conditions
of salinity?
Proxy Data
Anything in the Earth system that sensitively responds to
environmental conditions and is preserved over time can
provide proxy climate data from which we can reconstruct
past climate!
What do we mean by Proxy Data?
• Scenario: You are sitting in an office with no
windows- you’ve been there for hours
working on a presentation for your students.
Data source: Other teachers are coming in
and
out
• Interpretation: How can you determine what
the weather is like outside?
• What proxy data sources could you use to
deduce what it is like outside when you can’t
measure it directly with instruments?
Proxy Data
• Share your ideas here!
Proxy Data Exercise
To help students understand how proxy data can
give us useful information even though it isn’t
directly measuring climate, ask them to think of
times in their daily lives when they use proxy data
– whether they realized it or not.
One prompt might be to ask them what think it
means if fellow students come into the classroom
with wet umbrellas. Discuss how the umbrellas are
not measuring rainfall but they are a good indirect
indicator of rainfall.
Similarly, the proportion of people wearing
sandals, tank tops, parkas, etc. can indicate
temperature.
Summary: Proxy Data
Any line of evidence that provides an indirect measure of former
climates or environments.
Proxy climate data are found in a variety of natural archives
including tree rings, ice cores, sediment and rock layers, corals,
and dripstone (speleothems),
Some important proxy climate data sources found in these
archives include pollen, diatoms, seeds, insect remains, gases,
mineral species, and stable isotopes
Lets look at a couple examples of proxy climate data types….
Lots of people know about pollen!
Pollen Analysis
The proportion of pollen types released in the
environment reflects vegetation composition.
Pollen can be extracted from sediment and identified to
taxonomic levels ranging from family to species.
Willow
Grass
Beech
Pollen from different stratigraphic levels provides
information on vegetation at specific periods in the past.
Pollen records from lake sediment cores
tell the climate story for the local area.
• Plants are distributed across
the land based on temperature
and precipitation.
• Thus, plants living in an area
change as climate changes.
•Changes from layer to layer in a
sediment core can tell us about
changing conditions
Identifying Pollen
The view under light microscope
Pollen slide ready for examination
What do you see?
Key:
1=Hazel
2=Pine
3=Grass
A
(10,000 BP)
B
(2000 BP)
Pollen Diagrams
Illinois State Museum
The x (horizontal) axis shows the percent of total pollen for each of the taxa (plant
types) displayed. The y (vertical) axis shows age (time) and depth of sediment.
Radiocarbon dating (discussed later) is used to tell us how old the sediments are, and
when changes have occurred.
The North American Vegetation Story
•
Ice age visualization http://jesse.usra.edu
•
In these videos, note that each tiny dot is one sampling site containing pine
pollen! Bigger dots are where there are many sites with this taxa!
•Pine story:
After the last ice age, species
could migrate north to colonize
where there once was ice.
Ragweed story:
•This story is not so straight
forward. Something else is
involved besides climate
change. Any ideas? 
Any Questions about Pollen as a
Climate Proxy Data Source?
Try this Pollen analysis
Student Activity:
http://www.ucar.edu/learn/
1_2_2_10t.htm
Proxy Example 2: Oxygen Isotopes
Light Oxygen
Oxygen-16
8 neutrons, 8 protons
Lower mass
Very common
(over 99% of oxygen)
Heavy Oxygen
Oxygen-18
10 neutrons, 8 protons
Greater mass
Less common- about
..2%
Their different mass causes them to be unevenly
distributed in the atmosphere and hydrosphere.
Oxygen Isotopes & the Water Cycle
 As air cools by rising into the atmosphere or moving
toward the poles, moisture begins to condense and fall
as precipitation.
 At first, the rain contains a higher ratio of heavy oxygen,
since those molecules condense more easily than water
vapor containing light oxygen.
 As the air continues to move poleward into colder
regions, it becomes depleted of heavy oxygen.
 The snow that forms most glacial ice develops a higher
concentration of light oxygen
 During glacial periods, more and more light oxygen is
locked up in ice sheets, changing the ratio of light to
heavy in the oceans.
Oxygen isotopes measured from ice cores
• Scientists can measure the ratio of heavy and light
oxygen directly from ice sheets.
• Ice sheets contain a record of hundreds of thousands of
years of past climate.
• Scientists recover this climate history by drilling cores in
the ice.
Lake Vostok Drill Site, Antarctica
GISP2 drill site, Greenland
Oxygen Isotopes Measured from Ocean Cores
Scientists can also measure oxygen ratios of Foraminifera and
other microfossils in ocean cores because they build their
calcium carbonate shells using oxygen from the ocean water at
the time they were alive.
Foraminifera: single celled organisms
with shells made of calcium carbonate.
Images:IODP
Oxygen Isotopes, Ice Volume & Sea
Level
Long-term variations in the ratio of the isotopes
oxygen-16 and oxygen-18 reflect not just
temperature but are a direct indictor of ice-sheet
volume, and indirectly, sea-level.
Any Questions?
A great resource to assist high school students to understand stable isotopes:
http://oceanexplorer.noaa.gov/explorations/03mex/background/edu/media/mexdh_growth.pdf
Time: How do we know when?
Time: How do we know when?
Why do we need to date things?
In order to talk about relationships between different
events we need to know:
Did event A precede or follow event B?
Is B older or younger than even C or at the same time?
How long did it last?
Different methods useful for different time periods, from
hundreds – to millions of years ago (mya).
Relative Dating
Relative Dating
Stratigraphic position (stratigraphy)
Law of Superposition
Which cake layer is put on the plate first?
Can you put the second layer on first?
Relative Dating
Have students think of examples of relative
dating in their own lives
Your friend has two
brothers.
Can you tell who is older?
Can you tell exactly how
old he is?
Relative Dating
Have students think of examples of relative
dating in their own lives
Can you tell which car is oldest? Newest?
Can you tell exactly how old any of them are?
Absolute or Radiometric Dating
Absolute or Radiometric Dating
Radiocarbon Dating - C14
• Everything alive takes in
C14 via photosynthesis.
• When organism dies, C14
is no longer replenished
and begins to decay.
• Ratio of stable and
unstable carbon tells us
how long ago plant or
animal died.
• Half-life 5730 years
• ~ 40ka time limit
Absolute or Radiometric Dating
Radiocarbon Complications
• Radiocarbon samples taken and cross dated using
other techniques like dendrochronology show that the
ratio of C14 to C12 has varied significantly in the past
• Need to calibrate radiocarbon dates against material
of know age.
(Other Radiometric methods: e.g., KAr, UTh, Cl36)
Absolute or Radiometric Dating
Any questions?
Here is a 5-12 activity where students model the concept of half-life
using pennies or m&ms
http://www.esrl.noaa.gov/gmd/infodata/lesson_plans/Making%20a%20Model%20of%20HalfLife.pdf
Incremental Dating Methods
Incremental Dating Methods
Tree rings (Dendrochronology)
• Tree rings show an alternation between layers of lighter,
thicker wood tissue (cellulose) formed by rapid growth in
spring and much thinner, darker layers marking when tree
growth stops in fall and winter.
Incremental Dating Methods
In addition to this seasonal pattern, variations in temperature, precipitation,
wind and other climate factors produce year-to-year differences in the thickness
of rings.
These differences are the same for trees of the same species growing in the
same location and can be matched up to produce long time-lines, going back
thousands of years.
Tree rings provide not only a
chronlogy, but also serves as a
proxy climate data source!
Based on your count of the
tree rings, in what calendar
year did the wet year take
place?
Incremental Dating Methods
Questions?
Link for a good dendrochronology activity for 5-12 students:
http://www.ucar.edu/learn/1_2_2_11t.htm
Review: Methods to date Past Climate Events
• Relative Dating
• Radiometric
• Incremental Dating
Any Questions?
Let’s pause for questions
from the audience
What do we know?
Climate Change Throughout Earth History
For the last 500 million years the Earth’s climate has
experienced continuous change
Climate Change Throughout Earth History
Putting the Pieces Together:
A Short Story of Earth’s Long Climate History
By: all those Paleoclimatologists who study
different parts of the Earth System
Climate Change Throughout Earth History
500 mya
400 mya
300 mya
200 mya
Ice sheets can only grow when continents are at the poles.
Climate Change Throughout Earth History
500 mya
400 mya
300 mya
200 mya
Ice sheets can only grow when continents are at the poles.
Climate Change Throughout Earth History
500 mya
400 mya
300 mya
200 mya
Ice sheets can only grow when continents are at the poles.
Climate Change Throughout Earth History
During the Tertiary period Earth’s climate cooled as
continents drifted toward the poles and India smashed
into Asia causing the uplift of the Himalayas.
50 mya
35 mya
Climate Change Throughout Earth History
During the Tertiary period Earth’s climate cooled as
continents drifted toward the poles and India smashed
into Asia causing the uplift of the Himalayas.
50 mya
35 mya
Climate Change Throughout Earth History
Change from W-E oriented continents and E-W ocean circulation
to N-S oriented continents and ocean circulation
caused gradual cooling over the last 65 million years.
Climate Change Throughout Earth History
A big shift in amplitude and timing of climate change 3mya.
Corresponds to alternation between glacial and interglacial
conditions.
Climate Change Throughout Earth History
With the continents in the same positions for the last 3 mya, some
other not as long term mechanism must be causing the cycling
between ice ages and interglacials.
Pleistocene
Any ideas?
Present Day
Changes in the Earth-Sun Geometry
These orbital variations
cause changes in the
amount and distribution of
incoming solar radiation.
When the variations in all
three cycles line up just
right ice sheets build up
at the poles, albedo
increases and an Ice Age
is born!
Want to know more?
• For more information on this go to NOAA’s
paleoclimatology page:
• http://www.ncdc.noaa.gov/paleo/milankovitch.
html
Reconstructing Past Climates
1) Where we find our evidence
• (data sources)
2) How we get our data and what
do they mean?
• (data discovery
and
interpretation)
1) Time: How we know when
climate changed?
• (chronologies)
2) Telling the story
• (synthesis)
Reconstructing Past Climates: data
sources
• Where do we find
our evidence?
Reconstructing Past Climates: data
sources
• Where do we find
our evidence?
• Natural history
archives in the
Earth system!
Reconstructing Past Climates: data
discovery
1)How we get our data?
Reconstructing Past Climates: data
discovery
1)How we get our data?
By selecting proxy
data sets that are
Sensitive recorders
of changes in the
climate system
Reconstructing Past Climates: data
discovery
1)And, what is a proxy
data source?
Reconstructing Past Climates: data
discovery
1)And, what is a proxy
data source?
Proxy climate data
Provide indirect
Evidence of climate
Change- we don’t
Measure temperature,
But see the temperature
effects on an organixm, for instance
Reconstructing Past Climates:
Chronologies
1)Time: How we know
when climate changed?
Reconstructing Past Climates:
Chronologies
1)Time: How we know
when climate changed?
By using relative, absolute,
and incremental dating
technique on the proxy
data and their geological
contexts
Reconstructing Past Climates:
Synthesis
1)Telling the story
The more precisely we
understand the timing &
changes that have occurred
in our Earth systemmovement of plates,
changes in atmospheric gas
concentration, solar
variability, the better
Reconstructing Past Climates:
Synthesis
1)How do we know what we
know about climate today?
By understanding the
climate patterns of the past,
we have the context to know
that the rate, trajectory, and
mode of climate change we
see today is unprecedented
in the Earth’s history
Reconstructing Past Climates:
Synthesis
We know that the only way
that climate can change is if
the Earth’s Energy Budget
changes and
/ Outputs
Inputs ==
Many different factors can force changes in this
balance
Reconstructing Past Climates:
Synthesis
We know that the past
paleoclimate record has no
analogue for the rate of
change, trajectory, and
mode of change we see
today.
We can’t explain
contemporary climate change
Without human behavior
Reconstructing Past Climates:
Synthesis
We can’t explain
contemporary climate change
Without human behavior
Want to know more?
For no-cost, self study climate change tutorials
http://www.pbs.org/teachers/stem/professionaldevelopment/
Earth’s Climate History:
How do we know what we know?
Presented by: Dr. Russanne Low and Dr. Carole Mandryk
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