1. Schedule • April 18: Causes of the Warming • April 20: Future Climatic Change, Conclusions and Perspectives • April 23: Wrap-up • April 27: Final 1-3:50 pm

2. Muir Glacier 1941 Causes of the recent warming Muir Glacier 2004

3. What is the cause of the recent warming? • We have had about 0.7C of warming over the last 100 years • Clearly there are more greenhouse gases in the atmosphere….. • But what is the context? • Other long-term changes • Tectonic: The northern movement of the continents produces a slow cooling ~ 5-10C over the past 100 Myrs • Insolation has been dropping. This amounts to about 1C over the last 6000 years • Millennial-Scale oscillations?

4. CO2 • We have very good data on the natural range of CO2 during the past glaciations from the ice bubbles. • An aside on natural sources of CO2 • We passed the maximum natural range about 1900…. • At that point fossil fuels were only a fraction of total human carbon input

7. 200 Million Tons All volcanic inputs

8. CO2 • About half stays in the atmosphere • 15-20% goes into the biosphere • There are places with substantial “reforestation” (Eastern US for example) • Faster plant growth • 25-30% into the shallow ocean • CO2 is more easily dissolved in cold water

9. Methane • Even more extreme story with Methane. • We were outside the natural range well before the industrial revolution • Human sources are about double all natural sources • Methane accounts for about 16% of the total greenhouse-gas effect.

10. Let’s Pretend….. The short-term climate is driven by: The Sun Spot Cycle Dust from volcanic explosions ENSO (El Nino Southern Oscillation) “Anthropogenic Influence” Atmospheric CO2 buildup

16. Let’s Pretend….. The yellow line is the sum of JUST these 4 factors The black line is the instrumental surface temperature record (i.e. reality) Works pretty good…hunh? Make some predictions……?

17. Sulfate Aerosols • Like many things, the role of SO2 is complex • Like water….as a vapor SO2 it is a greenhouse gas, as a particle it has a cooling effect • BUT, it reacts with water vapor to form sulfate particles (and sulfuric acid…acid rain)

19. Brown Clouds • These are essentially smog due to human activity • Stoves • Cooking fires • Two effects • Absorb solar radiation and heat lower atm (2-3 km altitude) • Blocks Sunlight producing ground cooling • May effect the monsoons

20. Brown Clouds • This is not just a problem in Asia or China • What do you know about the 1952 London Smog? • December 5-9 • The fog there was so thick that people could not see their own feet! • About 4,000 people died (maybe as many as 12,000)

21. Global Dimming • Because of aerosols pollution, the brightness of the Earth's surface has dropped about 7% • This probably represents a net cooling due to more sunlight being reflected by the increased particle load in the atmosphere

22. Radiative Forcing • Remember, the Earth has a natural greenhouse effect • The greenhouse gases we have added has enhanced the back radiation by about 2.7 W/m2

23. But….the warming is actually pretty small… • We have increased CO2 by 35%, equivalent CO2 by 60% • Why ONLY a 0.7C temp increase? • Ocean Thermal Inertia • Aerosols • Insolation

24. The net effect of the various sources of radiative forcing is still a bit tough to sort out.

25. Greenhouse Gas Production