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We have decisively changed the carbon cycle, the nitrogen cycle, and the rate of extinction.
Just as human activity is upsetting Earth's carbon cycle, our actions are altering the water cycle.
The oxygen cycle, the nitrogen cycle, the carbon cycle, the water cycle - all of these are linked to the existence of life in the sea.
We cannot hope to either understand or to manage the carbon in the atmosphere unless we understand and manage the trees and the soil too.
Grief is an element. It has its own cycle like the carbon cycle, the nitrogen. It never diminishes not ever. It passes in and out of everything.
Unless we decide to reduce greenhouse gas emissions within just a few years from now, our destinies will already be chosen and our path towards hell unalterable as the carbon cycle feedbacks... kick in one after another.
The fact that we have been able to perturb the carbon cycle with our industrial revolution is evidence of how vulnerable we are - because when we destroy our environments, we destroy our food and energy supplies. In short, we destroy ourselves.
It's only been in the past two generations that we truly understood the impact our civilization has had on the natural world. To our credit as a species, we have turned this obscure scientific fact about carbon cycles into one of the most important political issues of the 21st century.
The world beyond 450 ppm atmospheric concentrations of carbon dioxide, the world that crosses carbon cycle tipping points that quickly take us to 1000 ppm, is a world not merely of endless regional resource wars around the globe. It is a world with dozens of Darfurs. It is a world of a hundred Katrinas, of countless environmental refugees
Some time ago we discovered the carbon cycle - a long-term set of chemical reactions that govern climates based on how much carbon is free in the atmosphere. At that point, it became clear that humans were affecting our environments far more profoundly than we realized. By releasing so much carbon and greenhouse gas into the environment, we're making long-term changes to every aspect of the natural world.
My first goal would be to reduce the perturbation in the carbon cycle. That would mean using carbon neutral sources of energy, and changing our agricultural practices to be less disruptive and polluting. I'm not talking about a policy here so much as changing the way our infrastructure works. That's why I'm so fascinated with changing the way we build cities, because they are the most developed forms of physical infrastructure for human habitation.
The essential fact which emerges ... is that the three smallest and most active reservoirs ( of carbon in the global carbon cycle), the atmosphere, the plants and the soil, are all of roughly the same size. This means that large human disturbance of any one of these reservoirs will have large effects on all three. We cannot hope either to understand or to manage the carbon in the atmosphere unless we understand and manage the trees and the soil too.