Volcanoes and Ice Ages
Causes of Natural Variability
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Key Points Past Variations in Global Temperature
– 100 yrs Warming + Volcanoes– 1000 yrs Medieval Optimum + Little Ice age– 10,000 yrs Post glacial– 1,0000,000 yrs Milankovitch Cycles
Volcanoes
Climate records from ice and sediment cores
Ice ages
Worldwide, most small glaciers are receding
El Nino Events and Global Temperature
The last 1,000 years
Note +/- 0.5 oC
South Western U.S. 1300 AD Why did these communities collapse?
Mesa Verde Cliff House
Since the end of the last ice age Note range of +/- 1 oC since 10,000 BP
Last Glacial Maximum
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Signs of Past Glaciation
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A million years of ice ages and interglacials
Estimated global surface temperature from ocean sediments
Present temperature 15 oC
Key Points Past Variations in Global Temperature
Volcanoes– Large volcanoes inject sulfate aerosols into
stratosphere– Sulfate aerosols reflect sunlight back to space– Cool the earth, but only for a year
Climate records from ice and sediment cores
Ice ages
Worldwide, most small glaciers are receding
Mount Saint Helens
May 18, 1980
United States Geological Survey
Atmospheric TransmissionInterrupted by large volcanoes
El ChichonMountPinetubo
Global temperature and volcanoes
Each event followed by a drop for 2-3 years
Key Points
Past Variations in Global Temperature
Volcanoes
Climate records from ice and sediment cores O18 (temperature), CO2, sulfate, ...
Ice ages
Worldwide, most small glaciers are receding
Drilling Ice Cores in Peru Annual layers in the
Quelccaya Ice Cap
Distant view of ice cap
Lonnie Thompson
Inca Country
Peru
Equator
Peru
Lonnie Thompson &Ellen Mosely Thompson
AnnualSignature
in O18
Quelccaya - 1976 Core Also measured are dust,
and sulfate CO2 , methane can also
be measured from ice cores, though not from this one
Drilling Ice Cores in
Greenland
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Key Points Past Variations in Global Temperature
Volcanoes
Climate records from ice and sediment cores
Ice ages– Last ice age ended 12,000 years ago– Changes over tens of thousands of years – Driven by Milankovitch cycles in Earth orbit– Recent evidence of abrupt transitions within 100
years
Worldwide, most small glaciers are receding
A million years of ice ages and interglacials
Estimated global surface temperature from ocean sediments
Present temperature 15 oC
Land Ice in the Northern Hemisphere (now vs 18,000 BP)
Alaskan Glacier
Photo Inge Bretherton
Greenland Ice Sheet
More great pictures (University of Cincinnati)
Key Points Past Variations in Global Temperature
Volcanoes
Climate records from ice and sediment cores
Ice ages– Last ice age ended 12,000 years ago– Changes over tens of thousands of years – Driven by Milankovitch cycles in Earth orbit– Recent evidence of abrupt transitions within 100
years
Worldwide, most small glaciers are receding
Milankovitch Cycles Small, predictable, changes in orbit of Earth
around the sun Departures from idealized elliptic orbit of
Newton, Kepler Precession: period 23,000 years Tilt: period 41,000 years Ellipticity: period 100,000 years Calculated in 1920’s but then no evidence Do not change total radiation reaching earth,
only distribution among seasons
Elliptic Orbit (Newton)
Ellipticity exaggerated For small sun, earth, orbit is fixed in space
Tilt
No tilt, no seasons
Present tilt 23.5o
Varies 22o - 24.5o
every 41,000 years
Precession - 1
Earth’s axis of rotation moves in space Because earth not quite spherical
– like a spinning top Earth now closest to sun in Northern
winter was/ will be in Northern summer
Period 23,000 years– About 12,000 years ago Hudson Bay ice cap
melted
Precession - 2
Incoming solar radiation Tilt + precession + ellipticity Varies with latitude Direct effects largest for continents
Key Points
Past Variations in Global Temperature
Volcanoes
Climate records from ice and sediment cores
Ice ages
Worldwide, most small glaciers are receding
Evidence for Ice Cap
Melting
1976 - Right– Clear annual
trace 1991 - Left
– Warmed and melted
Melting Glaciers
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Key Points
Past Variations in Global Temperature
Volcanoes
Climate records from ice and sediment cores
Ice ages
Worldwide, most small glaciers are receding
Sources of Information
Horel & Geisler Chapter 4,5 Lonnie Thompson and Ellen Mosely-
Thompson, Ohio State Universityhttp://polarmet.mps.ohio-state.edu/Icecore/Quelccaya.html
Thomas Lowell, University of Cincinnati http://tvl1.geo.uc.edu/ice/glacier.html