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Ice Ages and Climate Change

GLY 2010 – Summer 2013 Lecture 21

Discovery of an Ice Age• Louis Agassiz, a Swiss-

American scientist and physician, was the first to recognize evidence for an ice age

• Trained in medicine and natural history, he was the first to propose, in 1837, that earth had been subjected to a past ice age

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• 1807 - 1873

Louis Agassiz

• Agassiz moved to the United States in 1846• He became professor of zoology and geology

at Harvard University, and founded the Museum of Comparative Zoology

• He became interested in the last glacial advance in North America, and studied it for the remainder of his life

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Ice Ages• Ice ages - are times when the entire Earth

experiences notably colder climatic conditions• During an ice age

The polar regions are cold There are large differences in temperature from

the equator to the pole Large, continental-size glaciers or ice sheets can

cover enormous regions of the earth

Previous Ice Ages

• The climate history of earth is under active investagation

• Two Precambrian ice ages are known 2000 MYBP 600 MYBP

Late Paleozoic ice age, about 250 MYBP Pleistocene ice age

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LatePaleozoicGlaciation

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Plate Tectonics and Climate

• Glaciers can only form on land• As plates move, evidence for a cold climate, in

the form of glaciation, can only exist when land masses are present at high latitudes

• Movement of land masses also alters the oceanic circulation pattern, a vital factor in determining climate conditions

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Pleistocene Glaciation

• Began about 1.6 MYBP• There were at least 4 glacial advances • Climate cooled 5-10ºC during glacial

episodes, warming in between • Last episode peaked 18,000 years ago, ice

covering about 30% of the earth’s surface

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North American Ice Cover

• Figure shows the extent of ice cover from 18,000 to 8000 years ago

• White is ice, blue is glacial meltwater lakes

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Remnants of the Ice

• Loess is very fine sediment

• Extensive, thick loess deposits generally formed in areas bordering large, continental glaciers

• Loess is thickest just downwind of major river valleys

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U.S. Loess Deposits

Climate Questions

• What causes the onset of glacial conditions?• What caused the alternation of glacial and

interglacial conditions during the Pleistocene?

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Orbital Influence on Climate

• The earth’s orbit around the sun, and rotation around its own axis, influence climate

• Milutin Milankovitch proposed on theory of climate modification based on variations in incoming solar radiation, caused by orbital variations

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Variation in Orbital

Eccentricity

• The shape of the orbit changes over a period of about 100,000 years• The change is exaggerated in the drawing for clarity

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Tilt of the Rotation

Axis

• Varies over a 41,000 year period• Varies from 22.1 to 24.5 degrees

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Precession of the Axis

• Earth’s axis wobbles, or precesses, over time, like a spinning top• This means the axis points to different places in the sky over a

26,000 year period

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Milankovitch Hypothesis

• Milankovitch combined these ideas in a mathematical formulation that predicted their combined effect on climate fluctuations of the Pleistocene

• The three factors have almost no effect on the total amount of solar energy reaching the earth

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Orbital Variations and Climate Change

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Effects of the Milankovitch Hypothesis

• The effect of the various cycles is to change the contrast between seasons

• Milder winters in high latitudes lead to climate warming, and greater snowfall

• Cooler summers would reduce snowmelt• Combined, this might trigger ice formation, and

lead to an ice age• This can explain the alternating glacial-interglacial

effects seen in the Pleistocene19

Other Factors Effecting Climate

• Composition of the earth’s atmosphere• Variations in reflectivity of the earth’s surface

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Composition of the Earth’s Atmosphere

• We know the present composition of the atmosphere

• How can we measure it in the past? One method is to analyze gas bubbles trapped in

glacial ice at the time of formation Gas bubbles trapped in other substances, such as

amber, can also be analyzed Certain gases, such as carbon dioxide, methane,

and freon, are greenhouse gases21

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Greenhouse Effect

• Sun emits ultraviolet (UV - purple), visible (green) and infrared (IR -red) wavelengths

• Earth emits ONLY emits IR energy• CO2 traps IR, and greenhouse (earth) warms

Greenhouse Gases

• Polyatomic gases with three of more atoms may trap infrared radiation leaving the earth

• This radiation is earth’s cooling system• The gases act like a blanket, warming earth

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Global Warming

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Measuring Temperature Over Time

• It is easy to measure current temperatures• How do we measure temperatures at some

point in the past?• We use geothermometers

Most of these depend on the ratios of one isotope to another

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Oxygen Isotopes As Geothermometers

• There are three stable isotopes of oxygen, 16O, 17O, and 18O

• 18O is heaviest, and moves the slowest, so it is less like to be incorporated into oxygen containing compounds, such as water (ice)

• As temperatures increase, the probability of 18O being incorporated increases

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18O/16O Fractionation

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Oxygen Geothermometer

Data

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Ice Cores

• Ice cores in Greenland and at the Russian Antarctic station (Vostok) have provided radiometrically datable ice deposited more than 420,000 years ago

• Oxygen isotope studies give us an essentially continuous climate record for that period

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Other Climate Indicators

• Calcite linings in underground channels provide much longer climate records

• Calcite contains oxygen, so can be used as a geothermometer

• Records may go back hundreds of thousands of years

• Marine sediments have also been used for geothermometry studies

Stalagmite Evidence

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Temperatures at Glacial Maximum

• Differences between the annual mean near-ground air temperatures for present-day climate and for the climate during the last ice age approximately 18,000 years ago

Climate model calculation based on several sources of data

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Cenozoic Climate

Glacial Pair Photography

• On the left is a photograph of Qori Kalis Glacier taken in July 1978, and on the right, a photograph taken from the same vantage in July 2004

• Both photographs taken by Lonnie G. Thompson, Byrd Polar Research Center, the Ohio State University

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Muir Glacier

• On the left is a photograph of Muir Glacier taken on August 13, 1941, by glaciologist William O. Field; on the right, a photograph taken from the same vantage on August 31, 2004, by geologist Bruce F. Molnia of the United States Geological Survey (USGS).

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Sea-Level Changes

• When temperature changes, sea-level rises or falls, due to the melting of glaciers, and thermal expansion of sea-water

• Since 1900, sea-level has risen ~ 20 centimeters, and is estimated to rise as much as 100 centimeters by 2100

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Post-Glacial Sea-Level Rise

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Effect of Rising Sea-level

• Uncontrolled, sea-level rise by the year 2100 could lead to the erosion or inundation of 38% to 61% of existing coastal wetlands in the United States.

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Sea-level Rise: Florida

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North America if All Ice Melted

Effects of Sea-Level Rise

• Beach erosion• Salt water encroachment• Flooding of coastal areas• Changes to coastal wetlands• More information on climate change effects,

including sea-level rise, in the southeast is available at: http://www.epa.gov/climatechange/impacts-adaptation/southeast.html

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Bering Land Bridge

• Increased glaciation results in lower sea-levels, and may result in land bridge formation

• Ex - Bering Sea between Siberia and Alaska during Wisconsin glaciation

• Humans, mastodons, and mammoths migrated from Asia to N. America this way

• Camel and horse went the other way

Albedo

• Albedo is the reflectivity of the earth surface• Ice reflects a lot of radiation• Forests or sea-water are much darker, and

absorb more radiation• Absorption leads to heating, and reflection to

cooling, of the earth’s atmosphere and surface

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Effect of Albedo

• As ice melts, albedo decreases• Ice has an albedo of about 0.7, which means

70 of the nergy hitting a surface is reflected to space

• Ocean water has an albedo of 0.2• Thus, as ice is converted to water, heating

increases

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Effect of Meltwater on Glacier

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Arctic Ice Melt

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Arctic Ice

Levels

• In June 2012, the Arctic lost a total of 2.86 million square kilometers (1.10 million square miles) of ice, the largest June ice loss in the satellite record.

• Ice level in June, 2012 in the Arctic was the second lowest since satellite observations began in 1979 – this year isn’t far behind

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Petermann Glacier -

2012

• The calving of a massive 46 square-mile iceberg two times the size of Manhattan from Greenland's Petermann Glacier on July 14 - 18, 2012, as seen using MODIS satellite imagery

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Petermann Glacier - 2010

• The animation begins on August 5, 2010, and ends on September 21, with images spaced about 8 days apart

• A 100 square-mile ice island broke off the Petermann Glacier• It was the largest iceberg in the Arctic since 1962

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Geogenic or Anthropogenic Climate Change?

• Is climate change due to man or is it natural?• Maps show predictions from climate models

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Observed 1958-2008

• We are already seeing effects that resemble the models, which increases confidence in the models

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Current Drought Map

Animation

• About 4.3 percent of the contiguous U.S. fell in the exceptional drought category (D4)

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• Severe to extreme drought affected about 34 percent of the contiguous United States as of July 16, 2013, an improvement of about 3 percent from last year at the same time

Large Wildfires

• Large wildfires have been burning much larger areas in recent years• From 1884 to 1999 an average of 2.2 million acres burned

in the United States each year• From 2000 to 2008 the average increased to 6.4 million

acres• In Arizona, the Wallow fire is currently burning and has

become the largest fire in the state’s history, and the Horseshoe 2 fire currently burning is the fifth largest

• The figures are from a combined study by the Forest Service and the USGS

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Policy and Science• The Senate Committee on Energy and Natural Resources

hearing on June 15, 2011 discussed the relationship of fire to climate

• Forest Service Chief Tom Tidwell said, “Throughout the country, we're seeing longer fire seasons, and we're seeing snowpacks that, on average, are disappearing a little earlier every spring," - As a result, fire seasons have lengthened by more than 30 days, on average.

• He also cited devastating droughts• "Our scientists believe this is due to a change in climate," said

Tidwell

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Current Fire Status• IMT = Incident

Management Team, 1 being the worst fires

• Currently fire level is moderate (level III)

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Weather Disasters

• The drought of 2012 was a $30.3 billion event, and cost 123 lives, according to the National Climatic Data Center

• There were eleven billion dollar plus events in 2012

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• The U.S. has seen twelve weather-related disasters costing at least $15 billion since 1980, according to NOAA's National Climatic Data Center (expressed in 2012 $)

• Two of the top four most expensive disasters have been droughts