The Greens often say that social justice is a necessary part of environmental justice. How? There's a good example in an article from Le Monde by economist Thomas Piketty. It turns out that the rich are some of the biggest climate criminals on the planet, so solving the climate crisis means solving inequality:
However, it is increasingly clear that the resolution of the climate challenge will not be possible without a strong movement in the direction of the compression of social inequalities at all levels. With the present magnitude of inequality, the advance towards austerity of energy will be wishful thinking. In the first instance because carbon emissions are strongly concentrated amongst the rich. At world level, the richest 10% are responsible for almost half the emissions and the top 1% alone emit more carbon than the poorest half of the planet. A drastic reduction in purchasing power of the richest would therefore in itself have a substantial impact on the reduction of emissions at global level.
How? Private jets, multiple houses, big cars, and leisure air travel are some obvious answers. Higher taxation would help limit this environmentally destructive overconsumption, as well as providing the usual benefits of lower inequality (lower crime, better life expectancies, lower health costs and everything else). So if we want to save the planet, we really do need to tax the rich.