The generic term "environmental" sometimes invokes a moral code that all these groups tend to share, often with the perceptual psychology[?] notion that one's perception of one's environment, and of oneself, are always of a kind. One way to state the difference is that conservationists and ecologists advocate whats "good for you" -- while many environmentalists advocate what's good -- period.
In North America the early role models are Johnny "Appleseed" Chapman, Chief Seattle, and Thoreau. By word and deed, they argued that man belonged in harmony with nature, as its keystone species - in the terms of modern ecology. They saw no contradiction in altering or inhabiting the natural environment, and living in harmony with it forever. They did not resist development or colonization of lands - indeed [Seattle's Reply], 1854, was an agreement not to resist it.
Early environmentalists encouraged emulation of indigenous peoples and enriching the natural ecology with slow patient effort - Chapman alone planted millions of apple trees throughout the United States. The movement had little or no explicit political character. It was mostly aesthetic. It had no central doctrine. Most of its proponents did not know each other, but created a powerful discourse that influenced people strongly at the time.
By contrast with the conservation movement (an American invention of John Audubon and others who invoked Christian reverence for the Creation[?]), early [environmentalists] did not lobby for parks or human exclusion from "the wild". They did not see humans as apart from nature.
The harshest critic of the environmental movement in the 20th century was probably Ayn Rand, who considered it to be the opponent of human morality, creativity and industry. While carefully differentiating and not attacking the old American conservation movement, in her book "The New Left: The Anti-Industrial Revolution", 1971 (http://www.vix.com/objectivism/Bibliography/AynRand#TheNewLeft), she scoffed that the environmental movement was attempting to re-create the Garden of Eden - in defiance even of Judeo-Christian ethics which said that man did not belong there and could not return.
Some took her critique as a compliment. Others considered the criticism valid. A very few in deep ecology considered it both valid, and a compliment.
Largely due to this political critique and confusion, and a growing concern with the environmental health[?] problems caused by pesticides, some serious biologists and ecologists created the scientific ecology movement which would not confuse empirical data with visions of a desirable future world.
Today it is the science of ecology, rather than any aesthetic goals, that provide the basis of unity to most environmentalists. All would accept some level of scientific input into decisions about biodiversity or forest use[?]. Most would generally deny that there is such a thing as "environmentalism" and consider that phrase an invention of enemies.
One way to avoid the stigma of an "ism" was to evolve early anti-nuclear groups into the more scientific Green Parties, sprout new NGOs such as Greenpeace and Earth Action[?], and devoted groups to protecting global biodiversity and preventing climate change. But in the process, much of the emotional appeal, and many of the original aesthetic goals were lost - these groups have well-defined ethical and political views, backed by hard science.
However, the environmental movement today persists in many smaller local groups, usually within ecoregions, furthering spiritual and aesthetic values Thoreau or those who rewrote Chief Seattle's Reply would recognize. Some resemble the old U.S. conservation movement - whose modern expression is the Sierra Club, Audubon Society[?] and National Geographic Society - American organizations with a worldwide influence.
These "politically neutral" groups tend to avoid global conflicts and view the settlement of inter-human conflict as separate from regard for nature - in direct contradiction to the ecology movement and peace movement which have increasingly close links: While Green Parties and Greenpeace, for example, regard ecology, biodiversity and an end to non-human extinction as absolutely basic to peace, the local groups may not, and may see a high degree of global competition and conflict as justifiable if it lets them preserve their own local uniqueness. This seems selfish to some. However, such groups tend not to "burn out" and to sustain for long periods, even generations, protecting the same local treasures. The Water Keepers Alliance[?] is a good example of such a group that sticks to local questions.
The visions and confusions, however, persist. The new tribalist vision of society for example echoes the concerns of the original environmentalists to a degree. And the more local groups increasingly find that they benefit from collaboration, e.g. on consensus decison making[?] methods, or making simultaneous policy, or relying on common legal resources, or even sometimes a common glossary. However, the differences between the various groups that make up the modern environmental movement tend to outweigh such similarities, and they rarely co-operate directly except on a few major global questions.