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?
Scientists say that by the year 2050, the world population will have increased (Or: will increase?/ will be increasing?) to almost 10 billion people.
If we do nothing against global warming, the temperature will have risen (Or: will rise?/ will be rising?) by three degrees Celsius by then.