Complex sentence: Although the company cites measurable reduced emissions, concerned environmentalists may not consider "any" reduction short of zero emissions to be a success, though, the "negative effects" on the climate are still considered a theory.
Split into simpler sentences: Although the company cites measurable reduced emissions, concerned environmentalists may not consider "any" reduction short of zero emissions to be a success. However, the "negative effects" on the climate are still considered a theory.