Jamais Cascio asks the obvious in this fastcompany piece about the climate change activist group 350.org. If we're already at 387, then how are we going to get back to 350? It not only requires cutting emissions to zero, but removing CO2 from the atmosphere as well. And there is scant discussion of how they would expect to do so... reforestation, biochar? As Jamais points out, these are slow to act.
"But getting back to 350ppm requires more than a rapid cessation of
anthropogenic sources of atmospheric carbon. It requires an
acceleration of the processes that cycle atmospheric CO2. Planting trees is an obvious step, but it's slow and actually doesn't do enough alone. We'll also need to bring in more advanced carbon sequestration techniques, such as bio-char. The combination of the two would likely bring down atmospheric carbon levels, given enough time.
Unfortunately, we may not have enough time."
The point of the 350 framing is that we're already past what could be
construed as a "safe" level. In other words, it highlights the danger
of potential tipping points and how we really have no idea how far
ahead they lie.