Has there been an increase in volcanic activity in the past few decades?
The scientific concensus is that there has NOT been a recent increase in volcanic activity. There are many factors at work here and it is all too easy to present data that appears to say something that it really doesn't. First, as populations increase, people end up living in many regions that were once considered remote, and if these happen to be volcanic regions then once unseen eruptions will now be reported. Plus the impact of volcanic events now ripples across the globe as seen in the 2010 eruption in Iceland. The same eruption, in 1500, would likely not have been as much trouble for the folks in England.
More importantly, nearly every inch of the Earth is now monitored by many satellites so volcanic activity occuring in even very remote areas, with little or no population, is instantly reported to volcano monitoring agencies. Coupled with the ability to communicate around the world and rapidly transmit information from very remote places, the world now knows of an eruption almost immediately.
Also, there is the natural randomness of natural events. It is unreasonable to expect that natural processes won't have some sorts of variations to them. Keep in mind that we have only been scientifically investegating most volcanic regions for a few hundred years. If there presently happens to be a cluster of eruptions, it would not necessarily signal an increase in activity.