Global Warming: The Debate Objectives: Define the uncertainties Describe the scientific process Analyze available data Explore solutions

Four debates 1)Is the climate changing? 2)Are humans responsible? 3)How severe will it be? 4)What should we do about it? Science Science/Policy Policy

Why trust science? The scientific method: Theory  Law 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

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 Gov’t Agency Peer Review Scientist Results Private foundationBusiness Scientific Method Peer Review

The Intergovernmental Panel on Climate Change (IPCC)

The Greenhouse Effect (Fourier 1824) Sunlight Heat Greenhouse gases Sunlight warms the earth The earth cools by radiating heat Greenhouse gases in atmosphere trap heat and re-radiate it back to surface Slide from M. S Torn, LBL

1. Is the climate changing? YES

Climategate 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 Michael Mann Phil Jones

Temperature has risen by 1.5 °F over land 9 of the hottest years of the century occurred in last 10 years

CO 2 concentrations are rising Charles David Keeling 2. Are humans responsible? YES

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 CO 2 Plant Growth Warming NutrientsDecomposition Negative Positive

Temperature increase by 2100 Soil carbon

Warming experiment Alaskan boreal forest

Measuring soil carbon loss

Warming reduces microbial activity

We find negative feedbacks CO 2 Plant Growth Warming NutrientsDecomposition Negative Positive

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