In some ways, these questions have always been part of modern American environmentalism.

Green Fire, released in 2011, is a documentary about Aldo Leopold's influence on modern environmentalism and revolves around the concept of thinking like a mountain.

And "modern environmentalism was a political and activist mass movement which demanded a radical transforamtion in the values and structures of society."

Edward Bok, editor of the Ladies' Home Journal from 1888 to 1919, stood at the forefront of modern environmentalism and the promotion of progressive causes.

His work underpins much of modern environmentalism.

The death toll formed an important impetus to modern environmentalism, and it caused a rethinking of air pollution, as the smog had demonstrated its lethal potential.

Guha calls Kumarappa, "The Green Gandhian," portraying him as the founder of modern environmentalism in India.

"We have become convinced that modern environmentalism, with all of its unexamined assumptions, outdated concepts and exhausted strategies, must die so that something new can live," they wrote.

Gore notes that these photos dramatically transformed the way we see the Earth, helping spark modern environmentalism.

The conservationist principles as well as the belief in an inherent right of nature were to become the bedrock of modern environmentalism.