The reason it's 'key' is because adopting a plant-rich diet and reducing food waste are pretty much the only items on this Top 10 list that any individual regardless of location can decide to act upon right now.

Given that agriculture generates ~24% of the world's greenhouse gas emissions including ~48% of global methane emissions, it's a good start that gets individuals thinking conciously about their impact and encourages more action at the grassroots level.

Of course the other issues are just as urgent but those are altered by innovation and governments through taxes and legislation, which can be pushed along with the support of a more climate-concious society.