1. The Science of Climate Change
Global Climate Change
The Science of Climate Change

31. Tipping points…
Here is one…

32. … COLLAPSE OF THE AMAZON RAIN FORESTS
Reserve of carbon in the soil: potential source of CO2 so enormous it dwarfs the amount stored in living vegetation
This carbon is finely balanced: a small change in temperature can turn the soils from an absorber of CO2 to an emitter
How?

33. Relationships…
Relationship of temperature to decomposition? – positive feedback loop
Hadley Centre’s vegetation model examined 5 plant categories
Broadleaf trees
Needle-leaf trees
Two principal kinds of grasses (C3 and C4)
Shrubs
What happens to the plants as CO2 increases?

34. When scientists examined the water falling in the western Amazon Basin, they discovered it was low in 18O. Water had been recycled into the atmosphere so many times that most of the 18O had been left behind to the east.
What does this mean?
Plants of the Amazon effectively create their own rainfall
How?
Volume of water transpired by them  forms clouds -> blown westward  moisture falls as rain  transpired…

35. How do plants transpire?
As CO2 levels increase  plants of the Amazonian rain forest will keep their stomata closed for longer  transpiration will be reduced  less rain
Hadley’s Centre: by 2100, levels of CO2 so high that Amazonian rainfall will decline dramatically, 20% of that decline due to stomata closures
Rainfall reduced from 0.2 inches/day to 0.08 inches/day by 2100; northeastern Amazon: zero rainfall
Then what?

36. Series of positive feedback loops
By 2100, earth’s atmosphere: close to 1,000 ppm
When? – signs of rain forest collapse around 2040; by 2100, rain forest cover would have been reduced from its present 80% to < 10%
Consequences: you tell me

38. So: What will you do? What kind of world do you want to live in?
What kind of world do you want to leave for your children?
Serious questions.