Heat-resistant icings/frostings

This youtube video shows 7 different frostings in 32C or 90F heat in time-lapse
http://www.youtube.com/watch?v=ptiFsI0rF4Q&list=PL2639AB7064048F68

You're absolutely right. Frosted layer cakes aren't necessarily popular in the heat of summer. I was mostly just trying to brainstorm how to make a frosted layer cake work in summer without melting into a (tasty) puddle. The coconut flour idea is a good one, though. The first time I worked with that stuff I was amazed at how absorbent it is!

There is a point at which you start to sacrifice flavor and texture in the name of structural stability. I have struggled with this issue every summer, and have found that the best solution is to just make other desserts. For one thing, when it is super hot, people aren't really craving a cloying, fatty frosting. Most people want something lighter and more refreshing.

Unless you specifically have to make a frosted cake/cupcakes/etc I would suggest a sponge cake topped with fresh fruit, and maybe some fresh whipped cream on the side to add at the last minute. In a perfect world, we would all have access to dry ice so we could take frozen desserts on picnics because that is really what everyone wants to eat in the heat.

There I go again making things overcomplicated! Sorry. The most helpful tip I could offer to heat-proof frosting would be to add something like coconut flour, which thickens and soaks up moisture.

90+ degrees. 90-100% humidity. Summer in Tennessee. The answers so far are very helpful, though. Thank you!

Check out Smitten Kitchen's Swiss buttercream recipe. I agree with the shortening suggestion in theory, but... Don't use it unless you really have to. If it's going to be under 25 Celsius you probably don't need it. I haven't tested the recipe mentioned above beyond that temperature.

I've found that Swiss or Italian bcream holds up well. How hot is the weather going to be? If it's going to be in the 80's or higher, I would use 1/2 butter and 1/2 shortening because from a chemistry perspective, the melting point of mixed fats is higher and creates a more stable buttercream. If you do this, make sure that you up the flavorings added. I did this for an outdoor wedding in SE Florida in the summer; the humidity was over 80% and the temp was 90F+ and it didn't melt a bit.

How hot and how humid? Swiss buttercream holds up fairly well, but I've never pushed it with humidity or a super hot day.