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Ice Ages and Climate Change GLY 2010 – Summer 2012 Lecture 21 1 Discovery of an Ice Age • Louis Agassiz, a SwissAmerican 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 • 1807 - 1873 2 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 3 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 4 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 5 Late Paleozoic Glaciation 6 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 7 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 8 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 9 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 10 U.S. Loess Deposits 11 Climate Questions • What causes the onset of glacial conditions? • What caused the alternation of glacial and interglacial conditions during the Pleistocene? 12 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 • 1879-1958 13 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 14 clarity Tilt of the Rotation Axis • Varies over a 41,000 year period • Varies from 21.5 to 24.5 degrees 15 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 16 the sky over a 26,000 year period 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 17 Orbital Variations and Climate Change 18 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 glacialinterglacial effects seen in the Pleistocene 19 Other Factors Effecting Climate • Composition of the earth’s atmosphere • Variations in reflectivity of the earth’s surface 20 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 gases 21 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 22 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 23 Global Warming 24 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 25 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 26 18O/16O Fractionation 27 Oxygen Geothermometer Data 28 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 29 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 30 Stalagmite Evidence 31 Temperatures at Glacial Maximum Climate model calculation based on several sources of data • 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 32 Cenozoic Climate 33 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 34 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). 35 Sea-Level Changes • When temperature changes, sea-level rises or falls, due to the melting of glaciers, and thermal expansion of seawater • Since 1900, sea-level has risen ~ 20 centimeters, and is estimated to rise as much as 100 centimeters by 2100 36 Post-Glacial Sea-Level Rise 37 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. 38 Sea-level Rise: Florida 39 North America if All Ice Melted 40 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/impactsadaptation/southeast.html 41 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 42 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 43 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 44 Effect of Meltwater on Glacier 45 Arctic Ice Melt 46 Arctic Ice Levels • In June, 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 47 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 48 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 49 Geogenic or Anthropogenic Climate Change? • Is climate change due to man or is it natural? • Maps show predictions from climate models 50 Observed 1958-2008 • We are already seeing effects that resemble the models, which increases confidence in the models 51 Current Drought Map Animation • Severe to extreme drought affected about 33 percent of the contiguous United States as of the end of June 2012, an increase of about 10 percent from last month – as of 7-2412, 46% Severe to extreme drought • About 55 percent of the contiguous U.S. fell in the moderate to extreme drought categories (based on the Palmer Drought Index) at the end of June • About 4 percent of the contiguous U.S. fell in the severely to extremely wet categories 52 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 53 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 54 Current Fire Status • IMT = Incident Management Team, 1 being the worst fires 55 Weather Disasters • The U.S. has seen twelve weather-related disasters costing at least $15 billion since 1980, according to NOAA's National Climatic Data Center • Two of the top three most expensive disasters have been droughts • The drought of 2012 could well make it three out of four • "It might be a $50 billion event for the economy as it blends into everything over the next four quarters," said Michael Swanson, agricultural economist at Wells Fargo & Co. in Minneapolis, the largest commercial agriculture lender • Only three $50 billion weather disasters have hit the U.S. since 1980 56