To put the number in perspective, that's a 40% increase in the estimated number of trees worldwide. That's a positively enormous increase, and would--by necessi

To put the number in perspective, that's a 40% increase in the estimated number of trees worldwide. That's a positively enormous increase, and would--by necessity--in large part be planted on and around existing agricultural land. That comes with a host of significant opportunity costs; just to start, population increases are projected to require a ~70% increase in food production from 2005 to 2050[0]. While there's a great deal of progress being made in improved agricultural efficiency and food waste reduction that will help lessen the environmental impacts of that increase, land for food production is still likely to directly compete with biomass plantations for carbon removal. There are also recent studies that highlight some of the potential environmental impacts of large-scale terrestrial carbon removal as a primary mechanism for reversing the effects of climate change. Optimizing for sequestration means converting the most productive agricultural land or using even more natural land, devastating either food production or natural ecosystems,[1] in addition to drawing heavily on water resources and fertilizers on a massive scale, risking other planetary boundaries.[2] The more realistic scenarios risk both, albeit to less catastrophic degrees, but do so by decreasing potential sequestration and limiting its effects on global temperatures. Put a bit glibly, it's jumping out of the frying pan into the fire. That's not to say that it isn't part of the solution. It is, as the first paper explicitly states in its conclusion, and "can significantly contribute as a “supporting actor” of the mitigation protagonist, if it gets started and deployed immediately." But it won't be a primary mechanism, nor will it reach anywhere near 1.2 trillion trees. Even the more limited "pertinent options available now, which include reforestation of degraded land and the protection of degraded forests to allow them to recover naturally and increase their carbon storage" need to be priorities. Other geoengineering proposals, such as possible solar radiation management techniques, might extend the period during which we can use tCDR and other carbon removal mechanisms to mitigate past emissions beyond just slowing the rate of temperature increase. But without drastic emissions reductions in the immediate future, all of those possible options become more difficult, with even more deleterious consequences. Not to mention more expensive. In other words, there's no easy or even optimal answer. Assuming, of course, that 1.2 trillion trees can be considered "easy." 0. http://www.fao.org/fileadmin/templates/wsfs/docs/Issues_papers/HLEF2050_Global_Agriculture.pdf http://www.fao.org/fileadmin/templates/wsfs/docs/Issues_pape... 1. https://pdfs.semanticscholar.org/a712/e761c2360f927cbff0ee54d64761bb5d0709.pdf https://pdfs.semanticscholar.org/a712/e761c2360f927cbff0ee54... 2. https://www.nature.com/articles/s41558-017-0064-y https://www.nature.com/articles/s41558-017-0064-y