1. Climate Change: An Overview of the Science Anthony J. Broccoli Director, Center for Environmental Prediction Department of Environmental Sciences Rutgers University Conference on Carbon Politics and Finance Fordham University New York, NY October 29, 2010

2. Why do we care about carbon emissions?

3. [Source: Intergovernmental Panel on Climate Change, Third Assessment Report]

4. Preindustrial Today [Source: Brook, E., 2005: Tiny bubbles tell all, Science, 310, 1285-1287.] Greenhouse gases are now higher than any time in the past 650,000 years.

5. Three lines of evidence link CO 2 and climate: Basic physics Observations Modeling

6. Three lines of evidence link CO 2 and climate: Basic physics Observations Modeling

7. Basic physics of CO 2 and climate If an object receives energy in the form of visible light, as the earth does from the sun, it warms up. The warmer an object is, the more energy it emits in the form of infrared light. CO 2 and water vapor are “greenhouse gases” that absorb infrared light, making it more difficult for energy to escape into space. This is the earth’s cooling mechanism that balances the heating from the sun’s visible light. Without greenhouse gases the earth would be much colder (i.e., its average temperature would be well below freezing).

8. The “atmospheric window” Infrared light can escape through atmospheric window CO 2 partially blocks atmospheric window

9. Te4Te4 Temperature 288 K255 K Temperature 288 K255 K temperature increases Te4Te4 more greenhouse gases ↓ infrared opacity increases ↓ effective radiating level rises effective radiating level

10. Three lines of evidence link CO 2 and climate: Basic physics Observations Modeling

11. Source: NASA/Goddard Institute for Space Studies

13. Northern Hemisphere Temperature Reconstructions “It can be said with a high level of confidence that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries” “…the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium.” National Research Council

14. Source: Polar Research Group, Univ. of Illinois

16. Three lines of evidence link CO 2 and climate: Basic physics Observations Modeling

17. What Are Climate Models?

18. Coupled Climate Model Schematic

19. Blue: Natural Pink: Natural + Human-induced

20. Variations among colored lines represents uncertainty due to uncertainty in future emissions. Projections of Future Climate

22. Source: NOAA Geophysical Fluid Dynamics Laboratory Simulating Future Climate Change

23. Potential Climate Change Impacts

24. Future Emissions Scenarios All scenarios show increasing emissions during next several decades Some scenarios show decreased emissions in latter half of 21 st century Even with substantial reductions in emissions, CO 2 would rise to 2x preindustrial levels

25. The Atmospheric CO 2 Balance Human-produced emissions of CO 2 Uptake of CO 2 by ocean, vegetation, and solid earth

26. More Warming in the Pipeline Warming to date Additional “zero-emission” warming (aka “commitment”) Future emissions

27. Outstanding scientific questions How sensitive is the earth’s climate? In other words, how much will the climate change for a given change in greenhouse gas concentrations? How rapidly will sea level rise? Will Greenland and Antarctica melt more quickly or more slowly? How will climate change affect precipitation patterns? How will climate change affect severe storms (e.g., tornadoes, hurricanes, nor’easters)? Are there “tipping points” in the climate system? What impacts will climate change have on natural systems and society?