Hickel and colleagues find that, in 2021, the economies of the global North net-appropriated 826 billion hours of embodied labour from the global South, across all skill levels and sectors. Unequal exchange is understood to be driven in part by systematic wage inequalities. They find Southern wages are 87-95% lower than Northern wages for work of equal skill. While Southern workers contribute 90% of the labour that powers the world economy, they receive only 21% of global income.
The statistics aren’t surprising really. If you were fresh off a subsistence farm with no fancy machine tools and minimal education, you’d have to work more hours to produce the same value of stuff. The process of building up capital and education is called “development”, and it’s well documented to work at raising wages.
I don’t scientifically see why the author would go straight to “systematic wage inequalities”, and I strongly suspect there’s some politics in the mix there.