Contrary to a 1989 prediction by the deputy executive director of the United Nations Environment Programme, a 2003 paper in the journal “Science” found that worldwide natural vegetation productivity increased by 6.2% between 1982 and 1999. 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, which is a vital ingredient for plant photosynthesis. Commercial greenhouses stimulate the growth of certain plants by increasing the CO2 content of the air to 600 parts per million, while the current level in earth’s atmosphere is about 410 parts per million.