The modelling approach involves several steps, beginning with the development of bottom-up national trajectories, followed by a comparison of the ambition levels of the national trajectories (…). Using data from the literature, target level corridors for key indicators such as heated living space per capita or passenger-kilometres per capita were defined, with a minimum floor, among others, shaped by decent living standards 9,10 and the maximum on 1.5

It’s a different usage of the phrase “bottom up approach” than I’m used to.

From the title I expected: grassroots initiatives that are expected to convince a sufficiently large amount of people, and have a large impact on carbon neutrality.

What the article seems to describe instead is a (1) top down, sim city like, approach to life. Where the authors assign an allowance to each sim (2) And then sum the individual allowances.

Part (2) is indeed, a bottom up approach. Just not the one I expected.