It has been argued that environmental terrorism is not true terrorism because it does not target human victims but instead targets logging trucks, SUV's, McDonalds etc. However, the FBI defined terrorism thus:
Terrorism is the unlawful use of force or violence against persons or property to intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives.
The inclusion of property is interesting because it somewhat blurs the line between vandalism, protest and terrorism. Should Greenpeace activists be put put in prison for life if they damage property whilst trying to coerce the government?
A number of underground organisations have sprung up that are involved in acts of ecoterror. The Animal Liberation Front and the Earth Liberation Front are two of the more famous of these (the ELF claimed responsibility for $12 million dollars worth of fire damage to a ski resort in Colorado). They have been connected with various arson attacks against McDonalds outlets and have a considerable organisational advantage in that members are only very loosely affiliated and act alone in many cases.
In a way, committing acts of violence in the name of saving the environment makes a lot of sense. If you take the view that the greenhouse effect, overpopulation, logging and nuclear weapons are going to kill us all anyway then why not unlawfully damage a bit of property in order to try and save the planet? At worst you'll just kill a some people a few generations early and ease population pressures while your at it.
What would be really scary would be if the industrialized world bred such contempt and anger in some microbiologist that they decided that mankind really has no place on this planet and set about engineering a doomsday virus to get rid of us and allow the planet to recover. Mind you, when I read about Dubbya's ideas about the Kyoto protocol and the logging of old growth forest here in Australia I have half a mind to become that mad scientist myself...muhuhuhaha!!! But seriously, put your rubbish in the bin, ok?