In the US or the UK, the tests are regularly re-normed to keep the average score 100. But if you use the UK/US average as a baseline to look at IQ scores around the world, then the "average IQ" globally is closer to 88, and dropping, despite the Flynn effect (whose effect has already maxed out in many developed countries, where IQ levels are sometimes now in decline). Generally, people in lower IQ countries tend to have more children, who then grow up to be low-IQ adults (again, generally speaking, and obviously not in every case), which leads to a global decrease in the average IQ. This chart/animation shows what the estimated average is in 2015, what it was in 1950, and estimates what the global average will be in 2050 (the animation takes a few seconds to load).
This 2014 article in the Daily Mail offers a good summary of the research being done into the global drop in IQ scores. Yes, I know, it's the Daily Mail (actually Mail Online), but it does provide concise and easily Google-able references to the main researchers in this field, for example Jan te Nijenhuis, Michael Woodley, and most (in)famously Richard Lynn and Tatu Vanhanen, who pretty much pioneered the idea of how nation-level IQs have major effects on a nation's outcomes (which research has made the duo pretty unpopular, as the implications of their work aren't pretty).