Here are the issues you chose as most important:

Globally:

resource depletion

global warming, climate change, melting Polar Ice Caps

destruction of Tropical Rainforest

dumping of chemical wastes in water

air pollution

adequate water supply

global cooperation in determining resource use

running out of oil, dependence on oil and all the problems that causes

destruction of coral reefs

general habitat loss

depletion of stratospheric ozone layer

overpopulation

In California:

need for energy conservation

loss of agricultural land

gas consumption

air pollution

supply of electricity

forest fires

setting a good example in wise use of resources

removing O'Shaughnessy  Dam and restoring Hetch Hetchy valley

general habitat loss

overpopulation