Deforestation from timber harvests and farmland conversions have led to 565 GtCO2 (billion tons of carbon dioxide) being emitted into the atmosphere. Taking into account natural regeneration on forestland, Houghton (2003, 2008) and Houghton et al. (2012) estimate that deforestation has caused a net loss of 484 GtCO2 since 1900 which is about one third of all manmade emissions. However, these estimates do not take into account the substantial investment into fire management, plantations, and replanting since 1950, as well as the effect of carbon fertilization on a younger forest. We compare the outcome of a deforestation scenario with subsequent forest management with what would have happened if the natural forest in 1900 had not been harvested thereafter. Deforestation plus forest management suggests current forests actually hold about 94 GtCO2 more today than they did in 1900. However, natural forests would have held an additional 186 GtCO2. Human activities on forestland have therefore caused about 92 GtCO2 of net emissions since 1900. The effect of manmade land use and land use change is relatively small compared to the 1294 GtCO2 from industrial emissions over the same time period (Marland et al., 2008).

木材采伐和农田转换造成的森林砍伐已导致 565 GtCO2（十亿吨二氧化碳）排放到大气中。考虑到林地的自然更新，Houghton (2003, 2008) 和 Houghton 等人。(2012) 估计，自 1900 年以来，森林砍伐已造成 484 GtCO2 的净损失，约占所有人为排放量的三分之一。然而，这些估计没有考虑到自 1950 年以来对火灾管理、种植和重新种植的大量投资，以及碳肥对年轻森林的影响。我们将森林砍伐情景的结果与随后的森林管理与如果 1900 年的天然林此后没有被采伐会发生的情况进行比较。砍伐森林加上森林管理表明，目前的森林实际上比 1900 年多持有约 94 GtCO2。然而，天然林会多持有 186 GtCO2。因此，自 1900 年以来，人类在林地的活动造成了约 92 GtCO2 的净排放。与同期工业排放的 1294 GtCO2 相比，人为土地利用和土地利用变化的影响相对较小（Marland 等，2008） .