[new_realist]

There are 3.04 trillion trees on earth.

[adrianN]

A tree absorbs around 20kg of carbon dioxide a year while growing. To sequester 38 Gigatons you'd need to plant and cut down and bury around 10^12 trees each year, give or take an order of magnitude or two.

[ekianjo]

Don't forget the oceans as part of the equation.

https://en.wikipedia.org/wiki/Ocean_storage_of_carbon_dioxid...