Use the definite article.
The following does not include the Comunicación section.
the environment
depletion, exhaustion
reef
forest
global warming
climate
pollution
damage
decrease
species, kind
hurricane
flood
danger
planet
Earth (i.e. our planet)
recycling
natural resources
jungle
drought
tree cutting
earth, soil
storm
activist
air
animal
atmosphere
cause
consequence
deforestation
ecology
environmentalism
ecotourism
extinction
fauna
flora
humanitarianism
obligation
protection
responsibilty
system
situation
whale
dolphin
sea lion
parrot
monkey
bear
bird
sloth
penguin
toad
turtle
to save (i.e. water, electricity, money, time)
to save (i.e. a person or animal)
to save, to stow away (i.e. a document or thing)
to help
to cause
to preserve, to conserve, to keep
to pollute
to take care of
to destroy
to exploit
to participate
to prohibit
to protect
to recycle
to be happy
to regret
to bother
to be sorry
to be a shame
to fear
ecological
marine (i.e. sea related)
environmental
wild
sustainable