I have a question about the past/present tense usage of the verb “count” here:
The study is the first to pinpoint an end to the burgeoning population. The scientists estimate there is an 85 percent chance the species will taper to about 8.4 billion by the year 2100. The current world population is counted at 6.1 billion.
Since the act of most recent counting is a completed act, shouldn’t “is counted at” be changed to “was counted at“?
No. “was counted” would imply that you are referring to a particular occasion on which a count was made.
But in fact, nobody has ever counted the population of the world directly – the figure is derived from many different censuses, surveys, and estimates: there is not single event of counting.
In fact, I think “counted” is an adjective here – though I think it is an odd one to choose: “estimated” or just “is 6.1 billion” seem more natural to me.