Greenhouse Effect Sun heats the Earth Heat gets caught in the layer of CO 2 and H 2 O vapor, continues to warm things up

Causes of Greenhouse Effect A.Decrease in trees –humans clear cutting - causes an increase in CO 2

B. Increase in fossil fuel burning – releasing more CO 2

C.Increase in human population – releases more CO 2 into atmosphere through respiration

Ozone Depletion Both a threat –Ground level interaction between sunlight and pollutants – toxic to animals respiratory systems And a gift –Shields us and all life from as much as 97% of the sun’s UV radiation

Ozone (O 3 ) Layer * Forms when UV radiation strikes oxygen molecules (O 2 ) in the stratosphere * Photosynthesis produces O 2 allowing for ozone- forming chemical reactions to take place * Shielding mutagenic effects of ultraviolet radiation (UV-B and UV-C) * Thickness varies w/ seasons * Thicker in spring than Autumn and at the poles compared to Equator

Ozone depletion Describes 2 related declines in stratospheric ozone 1. loss in total amount of ozone in the Earth’s stratosphere (↓4% per year from ) 2. ozone hole – seasonal decline over Antarctica ↓ almost 70% of pre-1975 levels and over North Pole ↓ 30%

Ozone depletion caused by gases which unbalance the ozone cycle toward the breakdown of ozone Chlorine and bromine gases have ↑ due to the use of chlorofluorocarbons (CFCs) for aerosols, refrigerants, cleaning solvents and fire extinguishers

Ozone Hole Ozone hole –Occasionally affects Australia and New Zealand –Decline in stratospheric temp. b/c when ozone absorbs UV radiation it is transformed into heat energy

Ozone depletion

When CFCs escape into the stratosphere, and when UV radiation frees Cl and Br atoms, these unstable atoms breakdown ozone CFCs can take 15 years to reach the stratosphere, and can remain active for 100 years EACH Cl can catalyze thousands of reactions to break down the ozone

Effects of CFC’s Lets in UV rays Hole in Ozone layer near Antarctica Continued decrease due to weather – winds, temp

Effects of ozone depletion Increase in skin cancers Decreased levels of vit. A Increased levels of vit. D Reduced abundance of UV sensitive nitrogen fixing bacteria – causing loss of crops Disruption of nitrogen cycle Disruption of ocean food chains