For the first time ever, Major League Baseball will standardize the way baseballs are stored during the regular season.'s Tom Verducci reports MLB will require each team to store baseballs in "an air conditioned and enclosed room" this year. Data will be collected and used to determine whether humidors are necessary in 2019. From Verducci:

Major League Baseball will install climate sensors in each room to measure temperature and humidity throughout the 2018 season. That data will be used to determine whether a humidor is necessary in individual storage rooms for the 2019 season.

The Arizona Diamondbacks are installing a humidor this season. Their room is designed to store baseballs at the MLB recommendations of 70 degrees and 50% humidity. The Colorado Rockies have used a humidor since 2002 for the same reason Arizona is installing one: to combat the effects of storing baseballs in dry conditions. Lack of moisture makes baseballs slicker and gives them a higher coefficient of restitution, or liveliness.

The reason for all of this is that last season MLB teams shattered the single-season home run record, and during the postseason, pitchers complained the ball was too slick, leading to inconsistent breaking balls.

Humidors in Colorado and Arizona were installed in an effort to neutralize the extreme hitter's environments at each ballpark. The ball flies in the thin mountain air at Coors Field and in the dry desert air at Chase Field, leading to inflated offensive numbers. 

Ideally, baseballs would feel and carry the same way in all 30 ballparks. That's not really possible, but humidors can help standardize things around the league. This season will be used to collect data. Starting next year, the balls figure to be much more uniform.