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