Soil has a saturation limit beyond which it can't absorb more carbon - eventually organic matter in the soil will decay and release CO2 at the same rate that new organic matter can be added. Trees only hold on to carbon temporarily, until they die and decay and the carbon is released back into the atmosphere.
Turning a field of grass into a forest might delay the impact of one year of energy use for Microsoft, but its not a sustainable practice. How will they delay the impact the next year? What's the plan for when that carbon is inevitably released back into the atmosphere as the trees decay?
Planting trees as a means of carbon capture is snake oil, and I believe the likes of Google and Microsoft are too smart to fall for it, so that begs the question - what's their true motive for doing this?
So the thing about trees is, there are right ways and wrong ways to plant them. It should be obvious that plantng a tree in a desert won't just lead to a forest, but the same is true to a lesser degree in most locations. It is necessary to choose the right locations that will have water available, and good soil, and some other conditions for the trees to thrive.
Companies doing it will most likely just dump a bunch of seeds or saplings in an area that won't support long term growth, claim the numbers, and then let the trees die off.
Planting trees as a means of carbon capture is snake oil, and I believe the likes of Google and Microsoft are too smart to fall for it, so that begs the question - what’s their true motive for doing this?
Money.
Appearing to be eco friendly reduces the chances of regulations that would make them have to change their terrible polluting practices. Any kind of carbon offsets are a distraction to reduce public or regulatory pressures that end up costing money.
That might work for a little while, but I suspect there is an upper limit to how many trees a bog can absorb over a given time before it stops behaving like a bog.