Does Longman Press make a mistake?

[gxiang]

I am reading a book published by Longman Publishing Press, in which I come across such a sentence which i think is controdictary with the grammar I learn. I wonder if Longman Press makes a mistake? Could you help me?

original: The most recent estimates suggest that by the year 2050, global sea levels will rise by an average of 38 cm.

I think it should be like: The most recent estimates suggest that by the year 2050, global sea levels will have risen by an average of 38 cm.

as I have learnt that sentence with "by + time in the future" should use a "will have done" structure. I am at a loss.

[Tdol]

I wouldn't call it an error, but it seems a bit sloppy- I would use the future perfect here.

[gxiang]

Thank you, Tdol.