Tim Flannery addresses these issues in his book Here on Earth. Flannery is an adherent to the Gaia hypothesis which makes him rather optimistic about the future. The concept of Gaia was first proposed and popularized by James Lovelock. Flannery quotes Lovelock to provide a concise statement of its meaning.
In other words, the planet is trying to maintain an environment in which life can thrive. There are limits to what nature can do and mankind is on a path to exceed those limits. An optimist, such as Flannery, has to believe that mankind can change its ways.
There is also a diametrically opposed view that would claim that the earth proceeds along its own path and life responds as necessary. If the earth was so fond of life why have there been so many mass extinctions over its lifetime? For example, 250 million years ago there was what is referred to as the Great Dying.
The precise causes of this event don’t seem to be well understood, but if Gaia was on duty she must have fallen asleep. Flannery himself provides us with other data that is also consistent with a view of Earth as cold, uncaring platform on which life struggles to maintain a foothold. He suggests that mankind had its own near-extinction event.
Volcanoes play a significant ecological role, but one would expect a less extreme application by a caring Gaia.
If the Gaians are true believers, then Peter Ward probably represents the agnostics. He wrote a book titled The Medea Hypothesis: Is Life on Earth Ultimately Self-Destructive? Medea was the mythological creature who got mad one day and killed her own children. The analogy was between Earth (Medea), and complex life forms (children).
"Ward argues that the Medea hypothesis can explain the great extinction episodes of earth’s prehistory, and he sees the current destructive path of our human species as a continuation of that process."
Ward suggests where global warming can lead. His explanation for the Great Dying would start with excessive warming from green house gases followed by slower ocean circulation which limits oxygen concentrations at the greater ocean depths. Lower oxygen allows
There are plenty of examples from the animal world to demonstrate that a population imbalance can grow to the point at which a species no longer has enough food sources to maintain itself and the population collapses. Flannery believes that mankind can avoid this fate. He quotes declining birth rates in developed countries as an indication that humanity is trending towards a more sustainable solution. While it is true that declining birth rates are occurring, it is not obvious that this has any element of altruism associated with it. It may be that individuals choose to limit the number of children they wish to support for entirely selfish reasons—for example, to enable themselves to consume more. While everyone seems to be predicting that world population will finally peak somewhat north of 9 billion people, the fact that this is occasioned by higher living standards indicates ever greater consumption of resources such as energy.
Flannery is not counting on lower birth rates as a solution. He argues that, in addition, the nations of the world must come together and collaborate on global solutions to limiting green house gases and other environmentally harmful toxins. He argues that small steps have been taken in this direction already, noting the elimination of chlorinated fluorocarbons that were depleting the ozone layer as an example. He chooses to believe (hope?) that mankind is capable of acting rationally and is capable of such high order cooperation.
He recognizes the difficulties in putting such a cooperative effort in place. Flannery reminds us that we evolved as creatures that placed great emphasis on instant gratification. He refers to this as "discounting the future." Given the choice of an immediate reward versus one in the distant future, we are programmed to focus more on the near term. This is logical for any species that evolved in a mode where the next meal was always in doubt.
It is hard to be optimistic about the future. The more one learns about the Earth and its potential for complex responses the more uncertain things become. We focus on carbon in the atmosphere, but read of enormous sources of methane that could play an atmospheric role. Now it seems we have to worry about sulphurous bacteria. Reality seems to be racing ahead of model predictions. There are known unknowns to worry about, but how many unknown unknowns are there? It is difficult to recognize the benign Gaian viewpoint when the world’s environment seems to be increasingly unstable.
Given that mankind still has time to reverse its course and rescue itself from its perceived fate, can it be accomplished? Can it collaborate and make the necessary sacrifices? Consider, for example, the economic crisis in Europe. The better part of two years has been spent nibbling on the problem rather than coming to a decision of shared sacrifice on a scale necessary to resolve the issue. If developed nations with rational leaders cannot address an immediate catastrophe expeditiously, how can we expect the world in entirety to address issues that always seem to be a decade or two in the future?
I don’t for a minute believe in the Gaia hypothesis, and it is difficult to believe mankind is capable of responding in time to avoid disaster. The outlook is rather depressing.