If servers in Pennsylvania regularly wrote "Thank you" on restaurant bills, their averageincome from tips would be significantly higher than it otherwise would have been.
The influence is greater elsewhere, especially in sub-Saharan African countries including Sudan, Burkina Faso and Niger, where climate change has driven the averageincome more than 20% lower.
A 2015 study in the journal Nature predicted that the averageincome in the poorest countries will be 25% lower by 2100 compared to a world without warming, while some of the richest countries—like the USA—could experience an increase in income.