Ice Ages and Climate Change Chestnut Ridge, NY Jan 23 in the
year 16,004 BC
Slide 2
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?
Slide 3
How do we know there were ice ages?
Slide 4
What is climate anyway? -Weather average >30 years Central
England Air Temperature 1659-Present What other records are there?
Modern Climate Records
Slide 5
Historical Records of Climate Painting of Winter on the frozen
Thames River, London Grove, 1988
Slide 6
Agricultural Records Ripening of grapes depends strongly on
climate Cold years delay harvest date
Slide 7
Geologic records of climate 1.Land-based evidence of glaciers
2. Deep sea sediments 3. Present ice sheets
Slide 8
Land Records: Moraines
Slide 9
Glacial Erratics Some rocks have been transported far enough by
glaciers that they no longer look like nearby bedrock
Slide 10
Glacial deposits in areas not currently glaciated Laurentide
ice sheet 18,000 years ago
Slide 11
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!
Slide 12
Evidence for more than one ice age! Penck and Brueckner, 1909
Cant we get any more detailed than this?
Slide 13
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.
Slide 14
Ocean Sediment Cores Cores at Deep Sea Sample Repository at
Lamont-Doherty Observatory
Slide 15
What is in a sediment core? Bond et al. (1997) Sand grains of
quartz and other minerals. Volcanic ash from local eruptions. Plus
clay, clay and more clay!
Slide 16
Shells of single-celled organisms called Foraminifera
Slide 17
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!
Slide 18
Chemistry of foraminifera in marine sediments depends on water
temperature! Emiliani, 1955
Slide 19
800,000 years of glacial cycles This is from marine sediment
cores
Slide 20
Climate of the last 2.5 million years
Slide 21
Ice Cores Sections of ice from the Antarctic Ice Sheet provide
a climate record stretching back to 420,000 years.
Slide 22
Ice Ages are Global Both northern and southern ice sheets
experienced glacial cycles SIMULTANEOUSLY.
Slide 23
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?
Slide 24
What determines Earths temperature? The balance between
incoming and outgoing solar energy The Greenhouse Effect keeps
Earths temperature livable.
Slide 25
Carbon dioxide matches glacial cycles!
Slide 26
Solar radiation and glacial cycles
Slide 27
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
Slide 28
How on Earth do you build an ice sheet?
Slide 29
Changes in the Earths orbit Minimize summer warmth to promote
ice sheet growth!
Slide 30
What about future ice ages?
Slide 31
Changes in the greenhouse effect may result from industrial
activity
Slide 32
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
Slide 33
Great Ocean Conveyor
Slide 34
What controls recent climate? The Sun! Black: Climate in the
North Atlantic region Blue: Solar activity
Slide 35
Slide 36
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.
Slide 37
Slide 38
Ice ages and human migration Matsch, 1976Lister and Bahn,
1994
Slide 39
Slide 40
Slide 41
Slide 42
Annual layers in ancient records
Slide 43
Ice extent during peak of last glacial period
Slide 44
What determines Earths temperature?
Slide 45
Where do you find interesting cores? RV Maurice Ewing, of
Columbia University Ships track from a voyage in 1998.
Slide 46
Solar energy reaching a point on Earth varies through time
Laskar 1993 data set