New Survival Sport: Ice Chunk Dodging

A big 'ol chunk of ice fell on a park in Oakland and apparently it wasn't frozen poo from a plane since it was clean and clear.  This is happening more frequently around the world and one theory has it that ice is forming on the bellies of planes and then falling off.  Another theory being put forward by a scientist is this:

Martinez-Frias speculates it is a natural phenomenon caused by global warming. According to his studies, every time such an incident occurs, it is precipitated by an unusual atmosphere in which higher altitudes are turbulent and cold. The cold helps create the ice. The turbulence helps keep it together in the sky.

As global warming continues to heat the earth, his theory goes, upper atmospheric temperatures become cooler, opening more opportunities for the ice to form.

My first question is this: even if it is coming from the bellies of planes why hasn't it happened before?  What has changed? 

My second question is whether or not anyone knows where I can buy a steel umbrella.