I wonder if I always need future perfect in sentences with "by the year ..." and "by then" or if using the will-future (simple or progressive) is also possible in the two sentences below. If the latter is the case, is there a difference in meaning?

  1. Scientists say that by the year 2050, the world population will have increased (Or: will increase?/ will be increasing?) to almost 10 billion people.

  2. If we do nothing against global warming, the temperature will have risen (Or: will rise?/ will be rising?) by three degrees Celsius by then.

  • will increase and will be increasing is just like the present simple and present progressive.
    – Lambie
    Dec 27, 2022 at 21:15

1 Answer 1


If the prediction is that the population will be 10 billion in 2050, it will have increased to that number by then.

During the next 28 years it will increase.

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