Can reforestation sequester our annual carbon emissions? Forests sequester and store substantial amounts of carbon every year, while each year humans emit substantial amounts of carbon into the atmosphere. Is it possible for forests to sequester as much carbon as we're currently emitting each year, and if so is there a rough estimate of how much reforestation would be necessary?

Of course with such drastic land use changes as it would require to reforest much of the Earth, humanity's carbon emissions would surely change. This is basically a thought experiment, or a rough analysis to highlight the potential (or lack thereof) for trees to sequester our carbon emissions.
Reforestation is a one-off gain in carbon storage. Once a forest is fully mature, the carbon cycles back into the atmosphere as trees die and decay or are burned. So no, this will not sequester all the emissions from fossil-fuel burning. It could help offset it in the short term, but probably mainly just offsets the carbon dioxide from deforestation.