science

All the pesticides used in agriculture, and untold other industrial waste products, are the larger factor on fertility, and driving the worldwide crash in sperm counts. Also the world wide crash in insect populations, down 90% worldwide since the 1990s.

Herbicides and crops engineered to take more of them are a big factor in that, and declining sperm counts aren't the only effects of such endocrine disruptors. We are fools to allow companies to low key poison everyone and everything to make a buck, and to believe them telling us we need to do so.

"The number of motile sperm per ejaculate also followed a seasonal pattern, even after accounting for temperature, indicating that factors other than heat—such as variation in lifestyle, daylight, or environmental exposures—may influence sperm motility."

I think this is one very interesting take, as I would have guessed different lifestyle in these seasons a huge factor.