Jeff Nelson has a theory about why scoring is slightly up after the first month of the baseball season.

“The Yankees seem to be scoring a lot of runs every night,” the Seattle Mariners’ reliever said.

New York Yankees infielder Todd Zeile has his own guess.

“I know when I was in Colorado, there wasn’t a lot of scoring there early last season and this year there is,” Zeile said. “Maybe that’s the difference.”

It turns out both Nelson and Zeile are right.

Teams are averaging 9.5 runs this season, up from 9.3 through April last season, according to the Elias Sports Bureau. That 2.2 percent increase in scoring can be attributed to the Yankees’ big bats and the thin air in Colorado.

Teams are combining for four more runs a game at hitter-friendly Coors Field a month into the season. Apparently, the humidor the Rockies used last season to make the balls less lively isn’t working as well this season.

“Every day I come here, something different happens,” Cincinnati manager Bob Boone said Wednesday after the Reds’ 13-11 win over the Rockies. “I’m sure I’ve seen that before — I just can’t remember.”

The Yankees are doing their scoring everywhere, averaging 6.6 runs this season after scoring 5.1 during the first month of last season.

Home runs are also on the rise after dropping for two straight years, rising 10 percent from 1.91 last year to 2.10 this season. That’s still well below the record-setting April 2000, when teams combined to hit 2.54 homers, and the 2.34 from 2001.

Last year’s drop in homers could be attributed to umpires calling the high strike, which hitters are now getting used to.

“You saw that dramatic change when they started to call that high strike, especially the high breaking ball,” Mariners manager Bob Melvin said.

“At times you still see it, but not as much. The big thing they’re trying to do is to get a uniform strike zone so guys know what to look for and don’t have to adjust to each umpire’s zone every night. That helps out the hitters and speeds up the game.”

Baseball is getting closer to its goal of reducing the time of game to 2 hours, 45 minutes. Last year, nine-inning games averaged 2:52 — 6 minutes shorter than the previous season. Through April, games this season are down to 2:47.

“It’s been brought to our attention — it’s something they’re monitoring quite specifically from the major league office,” Rockies manager Clint Hurdle said. “We have a meeting with the umpiring crew before every series when I talk to the crew chief about guys that they’re keeping an eye on that might warrant a little special attention about hurrying up to some degree.”