I am disappointed that Science has allowed an abstract of a, otherwise good, paper to say that planting trees is "our most effective climate change solution to date". This is factually wrong and certainly a distraction. 1/2
Planting trees is certainly an important part of the climate change mitigation portfolio, but are neither cheaper nor easier to implement than other options. Most importantly, it won't fix the climate problem, albeit it should be part of the solution. 2/2
it is also important to recognise that trees come with litter and soils, so a tree-only focus will always report a partial carbon balance of the true effect on climate, eg, more trees in a future warmer Russia and Canada can also have higher emissions from C-rich soils.
Bastin et al. Science paper provides a very welcome analysis with sound and robust methods; a new database with great new applications to explore C sequestration. However, authors need to be more careful in crafting top conclusions and not going beyond what the data supports.
Finally, the reader is left with the impression (final paragraph) that out of 300 Gt of anthropogenic C, 200 Gt can be removed by tree planting. Unfortunately, the carbon cycle doesn't quite work this way. See next.
When we emit 1 tonne of C, half of it is removed by the land and ocean sinks; the other half is accumulated in the atmosphere. Well, the same applies when you remove 1 tonne of C from the atmosphere, half tonne of C is released by the natural CO2 sinks. So, take half of 200 GtC.
You can follow @pepcanadell.