I want to emphasize the aspect of environmental education in my math class. Now I'm reasoning whether to do that with linear inequalities or terms with two variables - these are our next topics. The problem is more or less that I'm lacking a good idea. I would like to treat climate change or waste in the environment, but haven't got a good example where the terms or inequalities are a means to model the facts. So I hope you can give me a hint for such an example.
A new car has a carbon footprint of $15.25$ tons of CO2. Each year you drive a car, you contribute $4.6$ tons of CO2. If you want to buy a new car, and emit less than $100$ tons of CO2 total over your lifetime, how many years could you drive the car? Would it be realistic to drive your car for that many years? What other assumptions in this model might be unrealistic?
You could spice it up a bit:
Each tree you plant can absorb 48 pounds of carbon per year. You want to be able to drive the rest of your life with a clean conscience. About how many trees do you need to plant over your lifetime? How many acres of forest would that be? In your explanation, be sure to clarify any assumptions you make.
I suggest looking at some intermediate general science texts. Often there will be some simple computational problems involving very minor* algebra. You might be able to find some that appeal to you although you will have to see what part of the algebra sequence they correspond to. Green stuff has been of interest going back at least to the seventies. And often 7th-8th grade general science (sort of like pre chemistry and pre physics, the way pre algebra is pre algebra) have either part or most of the curriculum around environmental topics.
I would just caution you to keep it rather simple. Word problems can be hard, in general. And you don't want to pick ones that segue too much into needing to teach (or even explain) general science. But you can still find examples. But please make them extra easy.
Also, you may be able to repurpose an example or exercise to use the physical example but repurpose it to your chapter of algebra. For example they talk about biocentration (DDT getting worse as you go up the food chain) and in the context of ratios, but you can think how to steal the basic science concept and make up an example with an inequality or the like.
*Things like ratios, percents, unit conversions, etc. And while these may be rather minor in math land, having facility with this sort of simple calculation is very important as a scientist, office worker, etc.