Transcript Slide 1
Global Warming: The Debate Objectives: Define the uncertainties Describe the scientific process Analyze available data Explore solutions Four debates 1) 2) 3) 4) Is the climate changing? Science Are humans responsible? Science How severe will it be? Science/Policy What should we do about it? Policy Why trust science? The scientific method: Carbon dioxide is increasing Is the world getting warmer? The world is warmer today than in 1750 Measure tree rings, ice cores Yes, tree rings and thermometers show a warming trend Theory Law Why trust science? 1) The scientific method is objective 2) Science is peer-reviewed by experts 3) Ideas are funded, not particular answers Science funding Taxpayer Congress Private foundation Gov’t Agency Peer Review Scientist Scientific Method Results Peer Review Business The Intergovernmental Panel on Climate Change (IPCC) The Greenhouse Effect (Fourier 1824) • Sunlight warms the earth • The earth cools by radiating heat • Greenhouse gases in atmosphere trap heat and re-radiate it back to surface Sunlight Heat Greenhouse gases Heat Slide from M. S Torn, LBL 1. Is the climate changing? YES Climategate Michael Mann Phil Jones • Issues: data manipulation and sharing – Tree ring data do not match thermometers – No evidence that data were altered – Evading and disparaging skeptics is counterproductive • Public is losing confidence in climate science Temperature has risen by 1.5 °F over land 9 of the hottest years of the century occurred in last 10 years 2. Are humans responsible? YES Charles David Keeling CO2 concentrations are rising Can warming be explained by natural causes? No. Climate Model Simulations: (a) with only natural processes (solar, volcanoes) (b) with also anthropogenic gases and aerosols Major Findings of IPCC-4 • “Unequivocal” that Earth’s climate is warming • Greenhouse gases at highest levels in 650,000 years • “Very Likely” that increased greenhouse gases have caused most of the rise in temperatures since 1950 3. How severe will climate change be? It depends… California, relative to last three decades: Expect a lot of change relative to the past: Impacts on the biosphere: feedback loops CO2 Plant Growth Nutrients Negative Positive Warming Decomposition Temperature increase by 2100 Soil carbon Warming experiment Alaskan boreal forest Measuring soil carbon loss Warming reduces microbial activity Fungal DNA concentration (ng g-1 soil) 500 400 300 200 100 0 Control Warming We find negative feedbacks CO2 Plant Growth Nutrients Negative Positive Warming Decomposition Different results in permafrost: Big soil carbon losses Also consider ocean feedbacks 4. What can we do? • Mitigate = slow the rate of increase of greenhouse gases • Adapt = change infrastructure to deal with climate change • Manage = actively manage climate and atmospheric composition Increasing knowledge required Mitigation options Pacala and Socolow, 2004 Mitigation options Pacala and Socolow, 2004 Mitigation options Pacala and Socolow, 2004 Summary • Climate change is happening • Humans are the likely cause • The biosphere may respond in unpredictable ways • There are options to avoid climate change