The following seems to indicate atheism is rising globally. Although they state the gain is gradual and they don't cover many nations.
Belief in God rises with age, even in atheist nations
Exceptions to the "gradual gain" were Israel, Russia, and Slovenia where atheism was declining. To quote
"In Russia, comparing the difference between those who believe in God but hadn’t previously, and those who don’t believe in God but used to, researchers found a 16 percent change in favor of belief."
As I recall in the developed world the US is somewhat unique in having a vibrant Protestantism. Most of the developed nations that are highly religious are Catholic, Eastern Orthodox, or Muslim. A few of the more advanced Caribbean islands might also be highly-religious, Protestant, and developed but I doubt they studied them.
I don't know if this fits the topic, but I wasn't sure where to put it.