In 2018, the journal Nature published an analysis of "35 years' worth of satellite data" to "provide a comprehensive record of global land-change dynamics during the period 1982-2016." It found that "tree cover has increased by 2.24 million sq. km (+7.1% relative to the 1982 level)." The authors of the paper calculated with 90% confidence that their best estimate of +7.1% varies from +2.9% to +10.8%. Likewise, a 2016 paper in the journal Nature Climate Change found "a persistent and widespread increase" in "greening" or plant growth "over 25% to 50% of the global vegetated area" from 1982 to 2014, "whereas less than 4% of the globe" had less greening over this period. A major factor in this greening is higher levels of atmospheric carbon dioxide (CO2), which is a vital ingredient for plant photosynthesis.