1. EARTH’S CLIMATE PAST and FUTURE SECOND EDITION CHAPTER 15 Humans and Preindustrial Climate WILLIAM F. RUDDIMAN © 2008 W. H. Freeman and Company

2. Main Concepts Major steps in Human evolution Theories for connection between climate and Human evolution –Limited data for Human evolution and how that limits our ability to test theories Agriculture and its relationship to climate –Role of climate in development of agriculture –Role of climate in civilization collapse –Role of agriculture in greenhouse gas increases of last 8000 to 5000 yrs Role of climate in megafaunal extinction

5. Role of Climate? What does the figure on the right suggest about African climate changes while humans were evolving in the last 4 million years? –While planet cooling, Africa getting dryer and less forested –Causes of drying may be many: precession and monsoons, lower CO2, tectonic uplift

7. Scarcity of human bone Samples affects two things: 1)Ability to determine true age range of human ancestors 2)Ability to determine rate of evolution of human ancestors and traits

8. Did human evolution occur because of: 1)The change from forest to savannah? 2)Continuous variability in climate? Impossible to tell with sparse data set

9. Role of Climate in development of Agriculture Two possibilities presented: –Deglacial warming favored agriculture in fertile crescent generally –Younger Dryas cooling/drying concentrated people near water sources and led to agriculture Impossible to tell if either is correct!

10. Climate and Civilization Several major civilization collapses coincide with periods of intense drought Not surprisingly, other factors likely played a role: –War, overexploitation of soil/resources, affecting climate by cutting trees

12. What is the main difficulty with the idea that climate caused the megafaunal extinction?

13. Last 5 interglacial CO2 records from Antarctic ice cores

14. Last 5 interglacial CH4 records from Antarctic ice cores

16. Rice patties or glaciation?!

17. Models suggest we would be in the beginnings of the next ice age now if not for the current levels of CO2 and CH4