Original:  More recently, atmospheric scientists have come upon the phenomenon of the reduction of  sunlight reaching Earth's surface observing a nearly a 10\% decline since 1960.
Revised:  More recently, atmospheric scientists have come upon the phenomenon of the reduction of sunlight reaching Earth's surface observing a nearly a 5\% decline between 1960 and 1990, with evidence of a recovery since then.
Edit intent: meaning-changed