As several of the previous respondents indicated, the ecosystem would be a good way to start. A discussion on the impact of climate change, the BP oil spill, and other natural disasters could be discussed. Narrowing down your topic to our waters, air, or soil may be helpful.
You may get more of what you are looking for if you narrow your question down a bit.
I think that it is very important to protect the natural environment. We are using many of our natural resources but I do believe that we are gradually becoming more aware of how important it is that we monitor what we do to the environment.
Environment is what we have around us. Humans and all around them form environment.
This environment must be kept under proper care for the ecological balance. Otherwise, we will have to suffer. But, humans are gradually letting the natural environment go under threat. Water is becoming more contaminated, air is getting polluted, earth is getting intoxicated.
We need to rise awareness in all walks, a global awareness is essential; because it is high time now.
First of all, let me make the question clear. Is it "What should someone expect to explain on the above topic"? Well, I'll base my answers assuming that my interpretation is right.
Frankly speaking, there are various topics one could talk about regarding the topic above. Some may include how global warming affects the natural environment, or how development should coexist with environment to preserve the pristine nature.
More specifically, one could explain about the biological diversity in a well preserved natural environment, taking examples from reknowned rain forests such as the Amazon. Or one could explain how the sites of natural environment can be great tourist attractions.
There are A LOT of things to talk about on such a subject.