Agricultural productivity and climate

[Irbis]

I would like to know how much climate influences agricultural output - as we know, places with temperate climate (such as my country - Poland) have a growing season lasting roughly from April to October but places located in the tropics or the equator have a year-round growing season. How much does it influence the productivity of agriculture and, hence, population density?

[Roamer]

Seeing that, potentially, Africa and areas around the equator have the "best" climate, yet usually don't have the same output, i 'd say climate is mostly a restraining factor;

people can grow agricultural produce inside an area that has the minimal required climate, whether they do and how well depends on factors as economics, culture, technology.

 

When i was little there i had an atlas that showed a "wheat border" but i can't find it online.