It's a hard problem and I'd like to know too. When I was doing a MSc in environmental engineering we were careful to let the stakeholders decide what environme

It's a hard problem and I'd like to know too. When I was doing a MSc in environmental engineering we were careful to let the stakeholders decide what environmental problems are important based on their feelings and not try to prioritize ourselves. Part of it is practical, it's very hard to have stakeholder buy-in on problems they don't care about, but part of it is that I don't think there is consensus on how to do comparisons across problems. You have to make difficult value judgments. (How many kgs of CO2 is one beautiful pristine forest worth? etc.) Some keywords you could look into are multi-criterion decision analysis and ecosystem services. My intuition and back-of-the-envelope estimates say that household waste, recycling, and water use don't matter that much. I'm not too popular with the environmental committee at work because I like to remind them that their annoying, time-consuming eco-friendly intervention of the week matters an order of magnitude less than switching a single meal per week from beef to a veggie alternative. I think the big questions are: how big is your house? what type of energy do you use for heating/AC? how much do you drive/fly? do you eat animal products? For most people the rest is comparatively not super consequential. (With some exceptions of course, there are hobbies that are 100x worse than others. People around here drive snowmobiles with 2-stroke engines, they are much less regulated and produce horrendous pollution compared to cars.)