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Thursday, November 22nd , 2012.docx

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HUMA 1780
Carl Wolfe

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Science, Technology and the Environment (SC NATS 1840A) – Thursday, November 22 , 2012 nd Is Atmospheric composition of Changing? Accurate measurements of average CO c2ncentrations require isolated locations to avoid local anomalies 20% increase since 1960 confirmed by other stations Seasonal cycle reflects northern growing season Atmospheric methane has also increased Little evidence of any increase in water vapour. Why are GG Concentrations increasing? Recent changes in greenhouse gas concentrations may be of man-made (anthropogenic) origin:  Conversion of forests to crop fields;  Wood & Fossil fuel combustion  Increased biological (decomposer) activity from landfill;  Larger cattle herds Antarctic ice core measurements match up with period of industrialization  CO concentration increased by 40% since 1750 2  Methane concentration doubled since 1800 Attributing rise in GG concentration to human activities unambiguously is challenging The story so far… Greenhouse gas concentrations, which play a crucial role in determining Earth’s climate, are rising Hypothesis: Global warming is caused by an enhanced greenhouse effect, the result of rising atmospheric concentrations of greenhouse gases. Can this hypothesis be tested? No simple experiment can establish a clear causal link between GG and climate change. We resort to  Historical records  Mathematical models Mathematical Models (Climate Simulations): General Circulation Model (GCM): mathematical representation of atmosphere + processes within it + interaction with rest of ecosphere. Provide insight into how different climate processes come together to yield aggregate behaviour.  Predictive ability? Models divide atmosphere and surface into many grid cells  Equations describe processes within cells and between adjacent cells, and are solved simultaneously. Simulation: Numerical experiment attempting to capture at least some aspect of reality.  Inputs: A GCM, Sun’s power output, initial conditions;  Variable: Atmospheric GG concentration over time;  Output: Long-term climate forecast. Conclusions from GCMs:  Rising greenhouse gases can explain global warming:  A Doubling of CO 2oncentration by 2100 results in global average temperature increase of about 3 degrees (range of 2 to 4.5 degrees) (IPCC ’07) Projected Impacts (model-based): Changes in:  Temperature and precipitation patterns;
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