"Scientific" American tries to answer the question: If a 170-pound guy fails to hit a dead baseball over a fence 635 feet away, is lack of CO2 in the air the most likely reason?

Is Global Warming Causing More Home Runs in Baseball?: Scientific American

A changing atmosphere may be a bit player in the myriad things affecting home run hitters. Several baseball bean-counters have crunched the height and weight listings between now and a century ago. In 1910, the average major league hitter was 5 feet, 9 inches and 170 pounds, according to the roster listings of the day. In 2010, those numbers grew to 6 feet, 1 inch and 205 pounds. Ballplayers have grown steadily bigger and stronger. Diet, training and playing conditions have improved, bats and balls are precision-manufactured, the pitcher's mound has been raised and lowered, the strike zone shrunk and widened. Before we even get to the steroids, there are enough variables to manufacture legitimate doubt about climate change and homeruns.

Dead-ball era - Wikipedia, the free encyclopedia

Before 1921, it was common for a baseball to be in play for over 100 pitches. A ball would be used until it started to unravel. The early baseball leagues were very cost-conscious, so fans would have to throw back balls that had been hit into the stands. The longer the ball was in use the softer it would become, and hitting a heavily-used, softer ball for distance is much more difficult than hitting a new, harder one. There is also the argument that the ball itself was softer to begin with, making home runs less likely...Many ballparks had big dimensions, such as the West Side Grounds of the Chicago Cubs, which was 560 feet to the center field fence, and the Huntington Avenue Grounds of the Boston Red Sox, which was 635 feet to the center field fence. The dimensions of Braves Field prompted Ty Cobb to say that no one would ever hit the ball out of it.