Last year mlb sanctioned a study with some tall foreheads to determine factors leading to the increase in home runs. In a nutshell, they concluded:
1. It's not the ball. It's not juiced. However there is lower drag coefficient on balls which does improve carry.
2. Weather (temp, humidity, wind, etc) was/is not a factor.
3. Launch angle is overrated.
If you want to review the document it is here:
http://www.mlb.com/documents/7/9/4/278128794/Full_Report_of_the_Committee_Studying_Home_Run_Rates_in_Major_League_Baseball_052418.pdf