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McMaster University
Life Sciences
Luc Bernier

SHORT ANSWER REVIEW LECTURE 8 – FEEDBACK & CHEMICAL WEATHERING Feedback - Climate forcing makes initial climate change - Feedbacks amplify or dampen the initial response - Ex. Cooling climate à increased: temp., preciptation, & weathering à tundra replaces forests à higher albedo, more reflectivity à cooler climate Chemical Weathering & CO2 - Early earth: More greenhouse gases, weaker solar radiation - Modern earth: Less greenhouse gases, stronger solar radiation Carbon Cycles - Natural process allowing Earth to exchange CO2 between different components of the system and maintain temperature - Plate tectonics and volcanic activity plays role in balance of CO2 Chemical Weathering - Affects silicates and carbonates - Hydrolysis: Involves reaction with H20 (rain) forming acid rain which affects rocks on land Organic Carbon Cycle: - H2O + CO2 à H2CO3 (carbonic acid) *C in CO2 is organic, hence the organic C cycle - H2CO3 breaks down silicate rocks (Ex. Wollastonite which contains CaSiO3) on land yielding ions (Ca2+, Si4+, HCO-) which are transported to river/ocean water - Ions react with water to form CaCO3 and SiO2 which are used by shell forming organisms - When organisms die, they sink to the bottom, and get buried in the seafloor - *The buried shells are composed of CaCO3 which has inorganic C, hence the inorganic C cycle The Inorganic Carbon Cycle: - Seafloor undergoes subduction (seafloor spreading) and buried sediments (containing inorganic carbon) get melted forming magna - Magna provides a source of recycled CO2 for volcanoes to release - Volcanoes emit CO2 into the atmosphere which drives the organic carbon cycle again Chemical Weathering is a Negative Feedback System - Initial change à warmer climate à Increased: temp., precipitation, & vegetation à increased chemical weathering à increased CO2 removal by weathering à Reduction of initial warming - Initial change à Colder climate à Decreased: temp., precipitation, & vegetation à decreased chemical weathering à decreased CO2 removal by weathering à Reduction of initial cooling LECTURE 9 – PROJECTIONS OF FUTURE [CO2] Projected Carbon Emissions - Range of possible [CO2] provided by IPCC. Two paths: 1. 4 x CO2 2. 2 x CO2 - Which path will we take? - Ideally, we want to take the 2x path. Idea that we will shift away from the use of fossil fuels. This projection assumes that individuals, cities, and nations are going to take action.
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