Complex sentence: Long-term side effects from prolonged use of the vest are unknown although, prior to "Crisis on Infinite Earths," it was stated that overuse of the suit would accelerate Earth's climate into its next Ice age.
Split into simpler sentences: Long-term side effects from prolonged use of the vest are unknown. Although, prior to "Crisis on Infinite Earths," it was stated that overuse of the suit would accelerate Earth's climate into its next Ice age.