I think there is something important that must be understood : All species are modifying their environnement through their behaviour. The widespread environnemental damages that we do now is due historically to the order of magnitude of two exponential growth : first, in population and second in using energy and machines to augment our capabilities and make our lives easier, thus making a huge change in the environmental impact we have.
Regarding population, in western countries, the birth rate is below 2, which means that we are not on a long term growth. This part is already more or less managed, and the number of living people should be stable on the long term. No need to modify anything regarding population in my opinion.
The second exponential growth is the production / consumption we do. 335
(2% per year of growth, over 200 years, it's already 50 times more).
However, as you might have noticed, we don't feel that more rich compared to our ancestors, because we compare ourselves to our neighbour and what seems "normal" is slowly changing in our minds. Similarly, we don't feel what the world was like 100 years ago. (That's called baseline shifting : what was considered a big fish was not the same for our grandparents compared to us, as well as what is a "hot summer" or a "cold winter", or a crowded area, or normal job conditions, etc...) This is what makes it difficult today both to :
* Ask people to reduce their lifestyle (for them, it's "normal")
* Make them understand the long-term impact we have. (for them, it's "normal")
Now that the problem is clearer, here are two positive solutions (in the sense it wouldn't hurt anybody's ethics). We can fix it either by :
* Making people more rational (and interested in the long-term of the species, depending of how you see people nowadays), and thus, people would base their decisions taking the facts above into account more easily, because they'll know they are very lucky and the environment in great danger
* Giving people a long-term memory (maybe coming genetically from their parents), so that they'll remember (more or less) how it felt a long time ago. 335