LIVE INTERACTIVE LEARNING @ YOUR DESKTOP September 20, 2011 Earth’s Climate History: How do we know what we know? What DO we know? Why does past climate

LIVE INTERACTIVE LEARNING @ YOUR DESKTOP

September 20, 2011

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

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. ElementaryB. Middle/High SchoolC. College LevelD. Informal E. 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”?


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…


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


Yes!By the end of today’s presentation you will be able to explain why this is true to your students, too!

How do we know what we know?

The focus of today’s webinar:

1) Why climate changes

2) Where we find our evidence

3) How we get our data and what do they mean?

1) When: How we know when climate changed?

2) Telling the story

Reconstructing Past Climates• (Climate system)

• (data sources)

• (data discovery, modeling & interpretation)

• (chronologies)

• (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!

?


There is only one thing that can change the Earth’s Climate!

Change in the Earth’s Energy Budget!


Take home message: Climate change is change in

Earth’s Energy Balance!when

Inputs == Outputs

Earth’s energy budget is not in balance

/

Inputs > Outputs = WarmingInputs < 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

Glacial Sediments

Peat

Where we find our evidence: Ice

Alluvial Sediments

Eolian Sediments Peat

Where we find our evidence: Sediments

Glacial Sediments

Hypothetical Lake Bottom: yearly accumulation of sediments

Story inside the SedimentsFind an archive where climate information is stored in an organized way, so that we know the sequence of events!

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!

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.

Proxy Data Exercise

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 Proxy climate data are found in a variety of natural archives including tree rings, ice cores, sediment and rock layers, corals, including tree rings, ice cores, sediment and rock layers, corals, and dripstone (speleothems), and dripstone (speleothems),

Some important proxy climate data sources found in these Some important proxy climate data sources found in these archives include pollen, diatoms, seeds, insect remains, gases, archives include pollen, diatoms, seeds, insect remains, gases, mineral species, and stable isotopesmineral species, and stable isotopes

Summary: Proxy Data

Lets look at a couple examples of proxy climate data types….

Lots of people know about pollen!Lots of people know about pollen!

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.

Pollen from different stratigraphic levels provides information on vegetation at specific periods in the past.

Pollen Analysis

Willow Grass Beech

• 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

Pollen records from lake sediment cores Pollen records from lake sediment cores tell the climate story for the local area.tell the climate story for the local area.

Identifying Pollen

Pollen slide ready for examination

The view under light microscope

What do you see?

Key:1=Hazel2=Pine3=Grass

A(10,000 BP) B

(2000 BP)

Pollen Diagrams

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.

Illinois State Museum

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?

http://jesse.usra.edu/

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

http://www.ucar.edu/learn/1_2_2_10t.htm


Proxy Example 2: Oxygen Isotopes

Their different mass causes them to be unevenly Their different mass causes them to be unevenly distributed in the atmosphere and hydrospheredistributed in the atmosphere and hydrosphere. .

Heavy OxygenOxygen-18

10 neutrons, 8 protonsGreater massLess common- about ..2%

Light OxygenOxygen-16

8 neutrons, 8 protonsLower mass

Very common(over 99% of oxygen)

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.

• Scientists can measure the ratio of heavy and light oxygen directly from ice sheets.

• Ice sheets contain a record of hundreds of thousands of Ice sheets contain a record of hundreds of thousands of years of past climate. years of past climate.

• Scientists recover this climate history by drilling cores in Scientists recover this climate history by drilling cores in the icethe ice. .

GISP2 drill site, GreenlandLake Vostok Drill Site, Antarctica

Oxygen isotopes measured from ice coresOxygen isotopes measured from ice 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.

Images:IODPForaminifera: single celled organisms with shells made of calcium carbonate.

Oxygen Isotopes Measured from Ocean CoresOxygen Isotopes Measured from Ocean Cores

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

http://oceanexplorer.noaa.gov/explorations/03mex/background/edu/media/mexdh_growth.pdf

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).

Time: How do we know when?

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?

Relative 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


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)



Any questions? Here is a 5-12 activity where students model the concept of half-life using pennies or m&mshttp://www.esrl.noaa.gov/gmd/infodata/lesson_plans/Making%20a%20Model%20of%20Half-Life.pdf

http://www.esrl.noaa.gov/gmd/infodata/lesson_plans/Making%20a%20Model%20of%20Half-Life.pdf

http://www.esrl.noaa.gov/gmd/infodata/lesson_plans/Making%20a%20Model%20of%20Half-Life.pdf

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.


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?

Questions?

Link for a good dendrochronology activity for 5-12 students:http://www.ucar.edu/learn/1_2_2_11t.htm



• Relative DatingRelative Dating• RadiometricRadiometric• Incremental DatingIncremental Dating

ReviewReview: Methods to date Past Climate Events: Methods to date Past Climate Events

Any Questions?

Let’s pause for questions from the audience

What do we know?


For the last 500 million years the Earth’s climate has experienced continuous change


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


500 mya 400 mya

300 mya 200 mya

Ice sheets can only grow when continents are at the poles.


500 mya 400 mya

300 mya 200 mya



500 mya 400 mya

300 mya 200 mya



During the Tertiary period Earth’s climate cooled as continents drifted toward the poles and India smashedinto Asia causing the uplift of the Himalayas.

50 mya 35 mya


During the Tertiary period Earth’s climate cooled as continents drifted toward the poles and India smashedinto Asia causing the uplift of the Himalayas.

50 mya 35 mya


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.


A big shift in amplitude and timing of climate change 3mya.

Corresponds to alternation between glacial and interglacial conditions.


Present DayPleistocene

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.

Any ideas?

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 upat 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

http://www.ncdc.noaa.gov/paleo/milankovitch.html

http://www.ncdc.noaa.gov/paleo/milankovitch.html

1) Where we find our evidence

2) How we get our data and what do they mean?

1) Time: How we know when climate changed?

2) Telling the story

Reconstructing Past Climates

• (data sources)

• (data discovery and interpretation)

• (chronologies)

• (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!

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 recordersof changes in the climate system


1)And, what is a proxy

data source?


1)And, what is a proxy

data source?

Proxy climate dataProvide indirect Evidence of climateChange- we don’t Measure temperature,But see the temperature effects on an organixm, for instance


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: Chronologies

1)Telling the story

The more precisely we understand the timing & changes that have occurred in our Earth system- movement 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


We know that the only way that climate can change is if the Earth’s Energy Budget changes and

Inputs == Outputs


/

Many different factors can force changes in this balance

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


We can’t explain contemporary climate change

Without human behavior

Want to know more?For no-cost, self study climate change tutorialshttp://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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LIVE INTERACTIVE LEARNING @ YOUR DESKTOP September 20, 2011 Earth’s Climate History: How do we know what we know? What DO we know? Why does past climate