Development of the Global Environment

Transcription

1 Development of the Global Environment G302: Spring 2004 A course focused on exploration of changes in the Earth system through geological history Simon C. Brassell Geological Sciences simon@indiana.edu phone: (Spring 2004 home page) Part III: Climate Change Topics within Part III. 1. Long-term Climate Change. paleoclimate proxies approaches to climate interpretation icehouse and greenhouse worlds 2. Ice Ages and Modern Climates glacial/interglacial cycles ozone depletion 3. Future Global Environmental Change carbon dioxide and global warming ozone depletion

2 Controls on Global Climate Variables Causing Climate Change Solar radiation and Earth s reflectivity: intensity, latitudinal distribution, albedo. Volcanism; continental configurations, elevations spreading rates, weathering, relief. Ocean and atmospheric circulation: surface currents and deep water wind strength and direction Atmospheric composition: greenhouse gases. carbon dioxide (CO 2 ), methane (CH 4 ), ozone (O 3 ) Vegetation: types, abundance and CO 2 uptake Evidence for Climate History Approaches to Climate Assessment Present: measurement of climate parameters. direct: temperature, precipitation, solar radiation indirect: atmospheric gases, winds, ocean currents Past: proxies of paleoclimates in geological records interpretations based on biological, chemical, physical, and geological evidence Future: predictions based on global climate models requires climate data to build GCM s, understanding of processes multiple layered systems (ocean and atmosphere)

3 Climate Proxies Climate Tools Validated in Modern Systems Biological variability. assemblages of flora and fauna, tree ring widths, leaf characteristics Physical changes in water. isotopic fractionation reflected in teeth & bone Chemical (biogeochemical) responses to climate. various responses, often biologically mediated Geological characteristics linked to rock formation. distributions of evaporites, glacial deposits, weathering phenomenon Paleoclimate Reconstruction Approaches Temperature: warm or cold; Humidity: wet or dry Lithological (rock records) evaporites; coals, peats; laterite soils; dunes; glacial deposits (tillites, morraines, eskers) Chemical (isotopic records) 2 H, 18 O in water, planktonic and serrated benthic organisms, teeth entire Biological (fossil records) corals, plants, leaf shapes seeds, pollen, assemblages

4 Temperature Records Geological History of Earth s Global Climate Alternating episodes of warm and cold icehouse (glaciated) and greenhouse presence or absence of permanent ice Rayleigh Fractionation Isotopes in Rainfall 18 O and 2 H (D) in water changes with latitude! 18 O = -15!D = -110! 18 O = -5!D = -30! 18 O = -2!D = -6

5 Isotopic Fractionation Oxygen Isotopes in Ocean Waters A reservoir effect during glaciations snow is enriched in 16 O (accumulated in ice) ocean becomes depleted in 16 O, enriched in 18 O snow rain 16 O evaporates 18 O enriched river 16 O evaporates 16 O returns glacial 18 O/ 16 O ratio increases interglacial 18 O/ 16 O ratio unchanged Cretaceous Greenhouse World Elevated Levels of CO 2 Timing and Cause: 145 to 65 Ma. plate tectonics active with fast seafloor spreading rates, high CO 2 emissions. Evidence and Effect: ice-free world, no evidence of glaciation flora and fauna attest to warm climates in polar regions, e.g. development of night vision in dinosaurs surviving polar winters.

6 Paleoclimate Reconstruction Early Cretaceous from Rock Records Paleoclimate Reconstruction Late Cretaceous from Rock Records

7 Cretaceous Paleoclimates Influences on Climate Unrelated, variable phenomenon linked to sea level and volcanism centrosaurus in cypress forest Biological Changes in Cretaceous Diversifications, Extinctions prior to K/T

8 Geochemical Evidence of Warmth! 18 O Records Evidence from forams: planktonic and benthic versus present day Warmer oceans Greenhouse/Icehouse Transition Ocean Circulation and Connections Timing and Cause: 33.5Ma, advent of progressive global cooling. Antarctica isolated by opening of Drake Passage and Tasman Strait Atlantic widening opened deep water connection from N. Atlantic to S. Atlantic. Evidence and Effect: surface and deep ocean temperatures diverge ice build-up on Antarctica accumulation of cold, salty deep water

9 Circum-Antarctic Currents Eocene/Oligocene Boundary Event? Triggered isolation of Antarctica Deep water movement from N. to S. Atlantic Drake Passage Tasman Strait Changes in Ocean Circulation Deep Cooling Divergence of deep ocean and surface ocean temperatures as Atlantic fills with dense, cold, salty water creating thermohaline circulation.

10 Evidence for Global Cooling Advent of Ice Formation and Build-Up Eocene/ Oligocene Quaternary Ice Ages Global Cooling creating Icehouse Earth Timing and Cause: began at least 3Ma ago. variations in solar insolation ice build-up on Antarctica and in continental ice sheets. Evidence and Effect: widespread records of sequential sequence of glaciations and interglacials changes in vegetation, variation in CO 2 produced by changes in carbon cycle.

11 Evidence of Ice Volume Growth of Polar Ice Caps Based on! 18 O signals in foraminifera Quaternary Temperatures Sequence of Glacial and Interglacial Events Alternating episodes of warm and cold!global records reflected in ice volume and temperature sawtooth pattern showing slow cooling and rapid warming cause of climate fluctuations?

12 Evidence for Rapid Warming Records with High Stratigraphic Resolution Sea surface temperatures Timing of last glacial maximum Rate of ocean warming: 5 C in <400a Changes in Solar Insolation Function of Changes in Earth s Orbit Varies with latitude: Milankovitch cycles Watts/m 2 Thousands of years Milutin Milankovitch: calculated changes

13 Milankovitch Cycles Three Effects Eccentricity, Obliquity (tilt) and Precession eccentricity: Earth s orbit varies cyclically Eccentricity Cycle (100ka) more eccentric less eccentric Milankovitch Cycles Three Effects Eccentricity, Obliquity (tilt) and Precession obliquity: variation in the angle of Earth s tilt affects latitudinal balance of solar radiation Obliquity Cycle (40ka)

14 Milankovitch Cycles Three Effects Eccentricity, Obliquity (tilt) and Precession precession: Earth s orbit wobbles produces changes in the timing of the seasons. Precession of the Equinoxes (19ka and 23ka)