Probably sex is a vigorous physical activity. Too much heat make you uncomfortable when you do any activity including sex so you are less likely to f*** when it is too hot. On the other hand if you live in a cold climate that extra heat may be welcomed.

However, child mortality (which is a bigger problem in poor mostly warm economies) is a much bigger factor. The more likely your kid is to die the more you have a lot. This is rational economics it's diversifying. If one or two or three children die I can still count on the fourth. If every child lives I don't need to have more then one or two.

Bottom Line: Increase child survival rate and decrease population.

I do not have a scientific answer, but living in the Philippines this is the most fertile place I have ever been to, children dogs cats chickens every one of them seem to multiply, even my garden fish pond ended up full with unwanted fish.

All I know is that global warming is causing more women than men to cheat on their spouses during a vacation:

http://www.gadling.com/2010/07/22/women-...

I'd say that this might induce some to believe that AGW is causing increased birth rates for illegitimate kids so I'm not quite convinced that AGW infertility is that much of a problem.

try searching

tropical climate fertility

so you can do your own work

Like in Equatorial guinea which has tropical climate does it affect human fertility. I need this for an MUN it's really urgent and DO provide me with the link of the source you are using. Thank you in advance.