Global Climate Change The Science of Climate Change

Global Climate Change The Science of Climate Change

Tipping points… Here is one…

… COLLAPSE OF THE AMAZON RAIN FORESTS �Reserve of carbon in the soil: potential source of CO 2 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 CO 2 to an emitter �How? 32

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 (C 3 and C 4) �Shrubs �What happens to the plants as CO 2 increases? 33

�When scientists examined the water falling in the western Amazon Basin, they discovered it was low in 18 O. Water had been recycled into the atmosphere so many times that most of the 18 O 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… 34

�How do plants transpire? �As CO 2 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 CO 2 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? 35

�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 36

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.