Transcript Ice Cores - Lamont-Doherty Earth Observatory

Ice Ages and Climate Change
Chestnut Ridge, NY Jan 23 in the year 16,004 BC
Four questions of climate change
•What are ice ages?
•How do we know there were ice ages, and when did
they occur in the past?
•How do we get an ice age?
•What can we expect in the future?
How do we know there were ice
ages?
Modern Climate Records
What is climate anyway?
-Weather average >30 years
Central England Air Temperature 1659-Present
What other records are there?
Historical Records of Climate
Painting of Winter on the frozen Thames River, London
Grove, 1988
Agricultural Records
•Ripening of grapes depends strongly on climate
•Cold years delay harvest date
Geologic records of climate
1. Land-based evidence of glaciers
2. Deep sea sediments
3. Present ice sheets
Land Records: Moraines
Glacial “Erratics”
Some rocks have been transported
far enough by glaciers that they
no longer look like nearby bedrock
Glacial
deposits
in areas not
currently
glaciated
Laurentide ice sheet
18,000 years ago
Louis Agassiz
A Swiss zoologist and
paleontologist at the Swiss Academy
of Natural Sciences
In 1837 he proposed that the presence
of moraines and erratics were evidence
that glaciers once existed where they are
no longer found today….
and the science of reconstructing ancient
climate was born!
Evidence for more than one ice age!
Can’t we get any more detailed than this?
Penck and Brueckner, 1909
Climate records from
the ocean:
Sediment cores
These are vertical sections of mud and sand
taken from the ocean floor.
Everything that lives in the ocean
eventually winds up on the sea floor
Fine clay and the sand-sized skeletons of
plankton make up most of the material on
the sea floor.
Ocean Sediment Cores
Cores at Deep Sea Sample Repository at Lamont-Doherty Observatory
What is in a sediment core?
Sand grains of quartz and
other
minerals.
Volcanic ash from local
eruptions.
Plus clay, clay and more
clay!
Bond et al. (1997)
Shells of single-celled organisms
called Foraminifera
Why are ocean sediment cores great
climate records?
• They are continuous records
•They are datable by a variety of techniques
•They are available for many time periods
•They can be very detailed!
Chemistry of foraminifera in marine
sediments depends on water
temperature!
Emiliani, 1955
800,000 years of glacial cycles
This is from marine sediment cores
Climate of the last 2.5 million years
Ice Cores
Sections of ice from the Antarctic Ice Sheet provide a climate record
stretching back to 420,000 years.
Ice Ages are Global
Both northern and southern ice
sheets experienced glacial
cycles SIMULTANEOUSLY.
How do we get an ice age?
Before we can answer this question, we must know:
Why is the temperature of the Earth what it is?
What determines Earth’s temperature?
•The balance between incoming and outgoing solar energy
•The Greenhouse Effect keeps Earth’s temperature livable.
Carbon dioxide matches glacial
cycles!
Solar
radiation and
glacial cycles
Ice Sheets, the key to ice ages
Ice sheets can CAUSE global climate change
1. Bright ice reflects solar radiation, leading to cooling and more
ice growth.
2. Cooling the ocean surface causes it to absorb Carbon Dioxide (CO2).
Carbon dioxide is one of the most important gases that create
the greenhouse effect.
Scientists have reasoned that it is possible to cause a global
ice age by building an ice sheet in northeastern Canada.
These are called climate FEEDBACK MECHANISMS
How on Earth do you build an ice
sheet?
Changes in the Earth’s orbit
Minimize summer warmth to promote ice sheet growth!
What about future
ice ages?
Changes in the greenhouse effect
may result from industrial activity
Can climate change happen quickly?
•Many places are warmed by
ocean currents
•If these warm ocean currents
were diverted or shut off,
the eastern US and Europe
would cool
Great Ocean Conveyor
What controls recent climate?
The Sun!
Black:
Climate in
the North
Atlantic
region
Blue:
Solar activity
to summarize…
1. Global ice ages have come and gone regularly for almost
3 million years.
2. Geologic records such as sediment cores reveal climate history
3. Formation of large ice sheets is necessary to cause global cooling
4. Changes in the seasonal input of solar energy allow ice to grow
5. Ice ages may happen in the future, but changes in the atmosphere
caused by humans may alter the timing.
6. Small but important climate change may happen quickly.
Understanding how climate works on short time scales is the
major goal of current research.
Ice ages and human migration
Matsch, 1976
Lister and Bahn, 1994
Annual layers in ancient records
Ice extent during peak of last glacial
period
What determines Earth’s temperature?
Where do you find interesting cores?
RV Maurice Ewing, of Columbia
University
Ship’s track from a voyage in
1998.
Solar energy reaching a point on
Earth varies through time
Insolat ion 65 deg. North
560
540
520
Insolation (W /m2)
500
480
460
440
420
400
0
25000
50000
75000
100000
125000
Y ear s BP
Laskar 1993 data set
150000
175000
200000
225000
250000