Average annual per capita incomes in the US, Japan, and Western Europe are currently around $40,000, and less than $6,000 for the poorer half of the world’s population. The same logic that says we need our $70 more than the people of 2100 need an extra $500 dictates that we should tax the world’s rich more, as long as each extra $500 in first-world taxes generates as little as an extra $70 in poor countries per capita incomes.