Complex sentence: Over all the world GDP will increase with a factor between 5-25 in the emission scenarios, and it is questionable wether this form of assumptions will hold as several limits to growth appears to be upon the world.
Split into simpler sentences: Over all the world GDP will increase with a factor between 5-25 in the emission scenario. It is questionable whether this form of assumptions will hold as several limits to growth appears to be upon the world.