Climate back to normal by 2050?

Could synthetic limestone in the world’s concrete market and massive kelp farms to stimulate fisheries REALLY sequester 50 GT CO2 per year, sequestering a TRILLION TONS of CO2 by 2050 and putting us back to 300ppm? That’s the claim of the Foundation For Climate Restoration, and I’m slowly trying to work through their claims point by point and see if such a thing is even remotely feasible.
Download their PDF here (their original website seems to be going through some maintenance right now)

f4crDownload