What are some examples of environmental forces that have promoted social change?
Our world is what it is today, largely because of social change. Social change can take many forms, and can be initiated by many environmental forces. For example, the current “revolution” in social media and web 2.0 (e.g., Facebook, Twitter, etc.) was significantly initiated by technological advances in our environment.
From your explanation, I take it that you are not referring to environmental forces in the sense of climate or anything like that. Rather, you are referring more to things like technology. Given that, I would look at the Industrial Revolution and globalization as two examples of environmental forces that have promoted social change.
In both of these cases, social change has been brought about by a change in what is possible. In the case of the Industrial Revolution, it was the presence of machines that made change possible. With globalization it was first shipping technology and then communications technology (telephones, internet) that made change possible. In both cases, the changing levels of technology (as you say) "in our environment" have led to major social changes in the world. These changes in our environment have led to changes such as the rise of countries like China and to the emphasis on modernism and individualism that seems to come with industrial capitalism.