I am pretty sure the answer is population.
Answer:
Canadian Shield, Hudson Bay Lowlands, St. Lawrence Lowlands
Explanation:
Hudson has a very low population in the north, St lawrnece region has most the population in the south, and the most agriculture, the Canadian shield is heavy in natural resources like boreal forests and minerals, so large scale operations to extract these resources occur more there. Most people want to live in the city, further south where its warmer and you dont live next to clearcutting operations and coal mines.
It affects it because the temperature increases and oxygen concentration will decrease
