Two new studies reveal how altering the composition of trees in forests is influencing not only the carbon cycle, but air surface temperatures to a significant degree as well. The results highlight how human-made changes to forests hold more severe consequences than previously believed. Worldwide, reforested areas are increasingly prominent; for example, in Europe, 85% of forests were managed by humans as of 2010. Strong favoritism of foresters to plant more commercially valuable trees -- such as Scot pines, Norway spruce and beech -- has resulted in reforestation of 633,000 square kilometers of conifers at the expense of broadleaved forests, which decreased by 436,000 square kilometers since 1850