Causes of Natural Variability Volcanoes and Ice Ages Causes of Natural Variability To download: Shift LeftClick PowerPoint 97 Please respect copyright on this material

Key Points Past Variations in Global Temperature Volcanoes 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 xxx

Signs of Past Glaciation xxx

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 Transmission Interrupted by large volcanoes Mount Pinetubo El Chichon

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

Annual Signature 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 xxx

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 Present tilt 23.5o Varies 22o - 24.5o every 41,000 years No tilt, no seasons

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 xxx

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 University http://polarmet.mps.ohio-state.edu/Icecore/Quelccaya.html Thomas Lowell, University of Cincinnati http://tvl1.geo.uc.edu/ice/glacier.html