It seems to me that any slow-down would later be compensated with a speed-up to conserve energy. Not saying that the slow down wouldn’t cause some effects. And maybe the speed-up again would do the same.
The reduction in angular momentum of the Earth's rotation is compensated for by an increase in the angular momentum of the Earth-Moon system - i.e., the Moon recedes from the Earth, and the lunar month consequently increases in length.
What this article fails to make clear is: Why now? (Moreso than in the past?)
The Earth's rotation has been slowing down since it coalesced out of the primordial nebula, ca. 4.5 billion years ago. And the fact that the Moon is receding from the Earth (at a rate of approx. 1 cm per year) means that tidal forces (which can trigger earthquakes) are actually diminishing in severity.
This article is pure sensationalism, based upon a grave misunderstanding of the scientific facts.
Regards,