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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