Learn English – “I’ve just seen your message, it had been a while since you sent it.”

It's been a long time since I have read an interesting book.

"Why is it not present perfect + past simple? I understand the "it's been" part, since it's something that is still relevant or going on. But if I'm referring to a specific past event, why should present perfect even be considered?"

I was reading your statement, and began thinking. And although Hellion is correct when he said:

"in both of the sample sentences, you're not referring to a specific past event, but to a somewhat generic experience; you can say "It's been a long time since I have read an interesting book", but you shouldn't say "It's been a long time since I have read The Hobbit".

He forgot a detail.

What if the last time I had read an interesting book was indeed at a specific past event, for example, last month? Hence a completed action, my reading an interesting book, at a definite time in the past.

Could a person then say:

"It's been a long time since I read (simple past) an interesting book."

I believe the answer is yes. It is grammatically correct and makes sense.

Here is another example taken verbatim from "A Practical English Grammar" (A.J.Thomson A.V.Martinet):

"I've worked here since I left school"

Which means I have finished attending school (for whatever reason but the most plausible being I have graduated or taken my final year exams) and now I am working i.e. I am not a student any more but currently an employee.

As emrys says, it is the since which is awkward here.

I think what the Guardian author means is that the tipping point was reached not in 2005 or at some specific point since 2005, but in the years since 2005. This would reflect what Murray and King said in the 2012 Nature paper: "In 2005, global production of regular crude oil reached about 72 million barrels per day. From then on, production capacity seems to have hit a ceiling at 75 million barrels per day."

But the past perfect is correct here; the author is referring to what was said a year ago by Murray and King, who were referring to the years between 2005 and 2012. The title of the Murray/King paper at that time was in the present perfect: "Climate policy: Oil's tipping point has passed".