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?

What is climate anyway? -Weather average >30 years Central England Air Temperature 1659-Present What other records are there? Modern Climate Records

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! Penck and Brueckner, 1909 Can’t we get any more detailed than this?

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? Bond et al. (1997) Sand grains of quartz and other minerals. Volcanic ash from local eruptions. Plus clay, clay and more clay!

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, 1976Lister 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 Laskar 1993 data set