Create an outline of a lecture on global warming.
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I. Introduction
A. Definition of global warming
B. Causes of global warming
II. Negative Impacts of Global Warming
A. Increasing global temperatures 
B. Rising sea levels 
C. Changes in weather patterns 
III. Solutions 
A. Reducing carbon footprints 
B. Planting trees 
C. Switching to renewable energy sources
IV. Conclusion
A. Summary 
B. Takeaway message
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