_12_ClimateChange_09 - GEL 1 Lecture 12 Climate Change...

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1 GEL 1: Lecture 12: Climate Change (p. 789-798, Ch. 23 – read selectively) Ancient Climate Change . . . Through geologic time, ice sheets have advanced and receded over huge areas of the continents - numerous “Ice Ages” lasting several tens of millions of years over the past few billion years - the warm intervals of Earth’s climate history are called ‘ greenhouse’ phases and the cold intervals are called ‘ icehouse’ phases - geologists look for evidence in rocks to recognize past ice ages, specifically glacial sedimentary deposits and various geochemical signatures recorded in sedimentary rocks - major Ice Ages have occurred about 280 m.y.a., 450 m.y.a., 700 m.y.a., and 2.2 b.y.a., each lasting for several millions of years An example of Greenhouse climates from the Age of Reptiles . . . Today’’s global average temperature is 15°C (59°F). Using measurements of atmospheric CO 2 concentrations preserved in ancient soils, as well as abundant fossil evidence for globally warmer climates, it is estimated that the global average temp during the Cretaceous Age of Reptiles ~100 m.y. ago was 23°C (73°F). - atmospheric CO 2 concentrations ~ 100 m.y.a. were much much higher than they are today (~20x), accumulating slowly and naturally from the build-up of volcanic CO 2 - this research into ancient CO 2 levels, global temperatures and associated climate conditions is called paleoclimatology Pleistocene Ice Age . . . About 2 m.y.a. the global climate became significantly colder than it was previously (no consensus has been reached as to exactly why, although many models have been offered) - known as the Pleistocene Ice Age - with colder temps, continental ice sheets grew and migrated over much of the northern latitudes - at their maximum the northern hemisphere ice sheets attained thicknesses of 2-3 km - in North America, ice sheets extended across Canada and southward across New England and the upper Midwest - an ice cap crowned the Sierra Nevada, creating much of the spectacular scenery of the High Sierra - most of the serrated landscapes we see in the Rockies, the Sierra, and most high mountain ranges worldwide is the result of this most recent global glaciation
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2 - in Eurasia, ice sheets covered Scandinavia and northern Russia, and southward across northern Europe to the Alps - the continental ice sheet over Antarctica couldn’t migrate as much since it’s surrounding by oceans (that can’t support the weight of 2-3 km of ice) Effect on sea level . . . When glaciers grow, water is transferred from the ocean reservoir to the glacial reservoir on land. Consequently, global sea level falls. - during interglacials, water is transferred by melting glaciers back to the ocean reservoir,
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_12_ClimateChange_09 - GEL 1 Lecture 12 Climate Change...

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