Complex sentence: Of most concern in these anthropogenic factors is the increase in CO 2 levels due to emissions from fossil fuel combustion, followed by aerosols (particulate matter in the atmosphere) and the CO 2 released by cement manufacture.
Split into simpler sentences: Of most concern in these anthropogenic factors is the increase in CO 2 levels. This is due to emissions from fossil fuel combustion, followed by aerosols (particulate matter in the atmosphere), and the CO 2 released by cement manufacture.