The relationship between income and the environment is an interesting topic to consider on many levels.
In terms of per capita income, we might associate higher income with higher concern for the environment for a couple of reasons. Countries with higher per capita income have already progressed through a long period of economic growth and development, have witnessed loss of environmental quality and may develop preferences for higher environmental quality. People may develop a sense of environmental awareness only after they've seen damage first hand. Further, "green" goods and services are often more expensive than goods that create more environmental harm. In short, wealthier households 1) may have a preference for and 2) can afford to buy organic products, solar panels and electric vehicles.
There is a lot of data that you could use to support these arguments, including time series analysis of polls addressing concern for the environment (note that the dips in the green line are highly correlated with recessionary periods. Also note the spike during the Deep Water Horizon spill), cross section analysis of spending on "green" products by income levels, or membership in environmental organizations by income levels.
In terms of aggregate income measures, economic growth tends to result in a structural shift away from activities that create a lot of pollution. In the initial stages of growth, economies tend to transition from the production of raw materials to agricultural products and then to manufacturing (all of which are relatively "dirty" endeavors). Once "developed", nations tend to outsource these activities to nations with lower wages (following the principle of comparative advantage) and focus production on services and high-tech activities which are relatively clean. We can look at growth in emissions, pollution or rates of deforestation to support these claims. Over the course of this semester, we've seen numerous examples of the association between high discount rates and overuse of natural resources.
The above two lines of thought provide support for the Environmental Kuznets Curve (EKC) hypothesis, which suggests an inverted u-shape relationship between pollution (on the vertical axis) and aggregate income (on the horizontal axis). Overall however, the evidence is mixed at best. There is little doubt that richer countries use significantly more energy and have higher ecological footprints on a per capita basis than poorer countries. Aside: Here is a fun little quiz to measure your ecological footprint. Mine is pretty bad (144 basketball courts, yikes!), largely due to a lot of international travel, two cars and a fairly large house.
Why does the relationship between income and the environment matter? What are some research questions that could be addressed on these topics? How might a better understanding of this relationship (at the household or national level) lead to better policy?