The study found that human activities have influenced ozone levels in both the lower and upper atmosphere, challenging the idea that these regions have separate causes. Emissions of ozone precursors and halocarbons have had significant impacts on ozone levels. From 1850 to 2005, human activities led to a positive ozone forcing of 0.5 W/sq m in the atmosphere due to ozone precursors, and a negative forcing of -0.2 W/sq m due to halocarbons. The combined effect of ozone precursors and halocarbons resulted in a net ozone forcing of only 0.1 W/sq m, with halocarbons playing a smaller role than previously thought.