12/2/2010 1 Geog 1001: Climate and Vegetation December 2, 2010: Lecture 24: Human interactions and climate change Professor Holly Barnard Positive Feedback • Climate warms (+ change) > ice melts > albedo decreases > climate warms (+ change) – Positive X Positive = Positive Feedback • Climate cools (- change) > ice increases > albedo increases > climate cools (- change) – Negative X Negative = Positive Feedback Positive Feedback in High-Latitude Meltponds Figure HLC 1.1.112/2/2010 2 Negative Feedback • Climate warms (+ change) > increases evaporation > increases clouds > increases albedo > climate cools (- change) – Positive X Negative = Negative Feedback • Climate cools (- change) > decreases evaporation > decreases clouds > decreases albedo > climate warms (+ change) – Negative X Positive = Negative feedback Feedbacks • Think of them numerically: 10 X -10 = -100 -10 X -10 = 100 10 X 10 = 100 7 Feedbacks in the system Positive feedback Amplifies the signal Negative feedback Dampens the signal Is sea ice melt a positive or negative feedback? 8 CO2 and temperature changes12/2/2010 3 9 Critical concepts • Atmospheric [CO2] and temperature have been steadily increasing; the two are linked • Excess CO2 in the atmosphere comes primarily from the burning of fossil fuels • It is difficult to calculate how much temperature and CO2 will increase in the future because emissions are uncertain and feedbacks are difficult to quantify Earth’s Climate System It’s all about energy Figure 10.1 11 The greenhouse effect 1. Shortwave radiation from the sun warms Earth’s surface 2. Earth’s surface emits longwave radiation back into the atmosphere 3. Some longwave escapes to space 4. The rest is absorbed by greenhouse gases and radiated back to Earth 5. Increased concentrations of greenhouse gases trap more heat near Earth’s surface, causing increased temperatures 12 Major greenhouse gases Gas Concentration (atm) Lifetime (years) Radiative forcing increase (W/m2) CO2 386 100 1.66 CH4 1.8 12 0.48 N2O 0.322 114 0.16 CFC-11 0.000242 45 0.063 CFC-12 0.000536 100 0.17 from http://cdiac.ornl.gov12/2/2010 4 13 CO2 sources • Fossil fuels dominate • Land use change (deforestation) also contributes Deforestation 15 CO2 is not in steady state 16 How do we know that extra CO2 causes warming? O O C Basic physics Evidence from the past Evidence from climate models12/2/2010 5 Climate Change Indicators and Predictions • Long term records from ice cores, tree rings, sediment cores, etc. • Climate models (General Circulation Models) • Detailed understanding from satellite observations. – http://climate.jpl.nasa.gov 18 Paleoclimate records 19 Evidence from climate models Goal: to reproduce the historical temperature record with a climate model. • Model with anthropogenic forcing accurately reproduces past temperature • Model with no anthropogenic forcing cannot reproduce past temperature Temperature Anomalies12/2/2010 6 Global Temperature 22 What is the IPCC? • The Intergovernmental Panel on Climate Change (IPCC) was established by the World Meteorological Organization and the United Nations Environment Programme in 1988. • Its main objective was to assess scientific, technical and socio-economic information relevant to the understanding of human-induced climate change, potential impacts of climate change and options for mitigation and adaptation. • The IPCC has completed four assessment reports, developed methodology guidelines for national greenhouse gas inventories, special reports and technical papers. 1st report 1990 2nd report 1995 3rd report 2001 4th report 2007 23 An uncertain future Known Unknown Atmospheric [CO2] will increase. How much CO2 will we emit? Atmospheric temperature will increase. How warm will it get over different regions? Sea ice will continue to melt. When will the Arctic be ice free? Sea level will rise. How much of Greenland and Antarctica will melt? The ocean will acidify. Will species adapt? Oceanic temperature will increase. How much will ocean circulation change? 24 Emission scenarios The global economy will ultimately determine how much CO2 we emit in the future.12/2/2010 7 12/2/2010 The Problem: Snowmelt is occurring earlier. How do we adjust water resource management? What are economic impacts: agriculture, hydro, ski industry. Case Study 1: Climate change and water resources in California source: NOAA NOHRSC Snowmelt and Ski Industry Aspen Mountain: Temperature and Precipitation in 21st Century12/2/2010 8 Aspen Mountain: Snow Wetness Aspen Mountain: Snow Density in 2030 Land Use, Grazing, and Dust Earth’s Albedo12/2/2010 9 Dust Storms Dust Storms and Snowmelt Climate & Land Use Grazing-Dust-Snow Feedback • Increase grazing > decreased vegetation • Decreased vegetation > increased dust • Increased dust > decreased snow albedo • …………….. • ……………...12/2/2010 10 Arctic Vegetation Change and Albedo Arctic Vegetation Change and Albedo Arctic Warming, Carbon Emission Feedback Arctic Amplification Figure 10.3512/2/2010 11 Permafrost Thawing & Lakes Draining Arctic Soil Carbon Permafrost Melt and Methane Arctic Warming, Carbon Emission
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