Complex sentence: There are few studies of the health effects of long-term continuous exposure on humans and animals at levels below 1% and there is potentially a significant risk to humans in the near future with rising atmospheric levels associated with climate change.
Split into simpler sentences: There are few studies of the health effects of long-term continuous exposure on humans and animals at levels below 1%. The is an unknown risk to humans in the future with rising atmospheric levels associated with climate change.