Sustain, to keep in existence, maintain. Sustainable, capable of being sustained. Sustainability, the property of being sustainable.
There is at least one clear fact about human society. It is an integral part of the environment and the environment dictates how it functions. For human society to remain in a form similar to what we have developed historically, it must have a stable environment that contains most of its historical features. How society treats the environment affects its stability.
The environment is an intricate web of diversity, each part contributing to the whole. The total of that whole makes us what we are. Change a part and things function differently. Change too many parts and things change radically. One thing that must be done to prevent a radical change in the human society that has developed is to limit the impact on the environment so that the renewable resources that society depends on can be renewed at about the same level. Doing that is to achieve sustainability of renewable resources, without it society must adjust and become something else in order to survive.
The issue of sustainability has been has been around at least since Thomas Malthus, who wrote about limits of population growth in 1798 (An Essay On The Principals of Population), and John Stuart Mill who wrote about the end of economic growth in 1848 (Principles of Political Economy). By the end of the 20th Century sustainability had become an issue of concern in the environmental and scientific communities. Today, because it can no longer be reasonably ignored, it is being co-opted, just like the word "green," to disguise ideas and actions that really are not sustainable at all.
Some examples are things like "sustainable growth," a phrase that is actually an oxymoron. All growth has limits, it cannot be continued indefinitely. Then there is "sustainable mining," which implies that minerals are a renewable resource, something that defies logic.
The term is also described by some as an outcome resulting in an ideal world, often with a shopping list of things desired; things like "social wellbeing," "a vibrant economy," and "sustainable economy." Nice thoughts, no doubt, but also very distracting from the reality of the ecosystem problem that we face. Such complicated wish lists used to explain sustainability might make their creators feel good, but they run the risk of creating confusion, and open the door to opponents of sustainability to use that confusion to bury the issue.
The core problem that confronts society at this time is the declining ability of the ecosystem to provide what it has historically provided. The reduction of these provisions greatly overshadows any other issue that we face, and unless we focus clearly on the environment and a stable ecosystem all else we do may be for naught. A stable economy, for example, is not possible in a system that does not have a stable ecosystem.
Sustainability of renewable resources simply means that we manage renewable resources so that they can always renew at the level required to support society. That means that we must not over consume them.
Environmental sustainability is only tangentially a social problem, though our social practices affect it and will have to change to accommodate it. Environmental sustainability is first and foremost an environmental problem and nothing else can be resolved satisfactorily until the environment is dealt with.
There are those that argue that advances in technology can make better use of resources and allow us to maintain our consumption level. This is misleading. First, our consumption levels are already too high and need to be reduced. Second, technology only helps if the improved production it enables is not used to produce more than is already being produced. In other words technology is only beneficial if it reduces intake, not if it increases output.
Social justice is an important issue for progressive to address, but it is not a determining feature of environmental sustainability. It is true that unjust societies can have an adverse affect on sustainability, but it is also possible that some could not. Terribly unjust societies can be environmentally sustainable as long as they are not based on growth and do not permit the over exploitation of the environment.
For progressives dealing with sustainability social justice comes into play in the social remedies that are required to fairly spread the burden of changing the system from one of exploiting the environment to one of living sustainably within it bounds.
Social justice is futile without a sustainable environment, the reverse is not true. Without a sustainable environment the ecosystem changes with no guarantee that human society will survive, or if it does, in any but a much reduced form.
Human society is but one interacting part in an intricate ecological web. The nature of that web determines how society can function. How society functions also affects the nature of the web.
Significant changes in the environment will have an impact on human society. This impact may result in a society quite different from the one that we have now. Significant change in society can also have an impact on the environment. The magnitude of change that society has undergone since the start of the Industrial Revolution has altered the environment to the point that society is no longer sustainable in its present form.
The core problem facing us today is the necessity to stabilize the environment's production of renewable resources so that current or near current levels remain available to society now and in the future. All other problems are secondary.