Tomorrow morning, an unidentified object passes through the moon. By the time that anyone realizes that the moon has been destroyed, it is already too late to figure out what that object was. It came and went fast enough that we only know it was there by its obvious effect.

The moon is shattered into a handful of large pieces, and uncountable smaller ones. The good news is that while the moon is in pieces, so far it is still loosely together around its center of gravity, so the tides are mostly unaffected for now.

However, the worst is still to come. Over time, the chunks of the moon, through constantly collisions with each other, will create an increasing amount of secondary debris and spread out the accumulation of mass. A tiny fraction of this mass will fall onto the earth, but enough so that, in 2 years, the friction from the debris will cause firestorms that will make life on the surface of earth impossible for the next 5,000 years.

We have only modern technology, which means no terraforming and no FTL. The governments and people of the world are united and have put you in charge. You have 2 years. What is your plan to save humanity?