Lacking manpower would be a very difficult thing to conceive, as I think slavery was still very proeminent in the medieval islamic world, and while some scholars were against it and promoted the abolition of slavery (for muslims) they were a minuscule minority even until the 19th century. I read about a controversy in Morocco in the late 16th century emerging after Ahmad Al-Mansur decided to take thousands of muslim blacks and enslave them in Morocco where they would be working in the immense sugar farms they created in the Souss region, and that was regarded by the ulemas as innaceptable, because for them enslaving muslims just because they were black was sinful. That didn't change anything and a century later Moulay Ismail (another sultan) killed all ulemas against his plans of forming a new slave army "Abid Al-Bukhari" which was composed of, you guessed it, muslim black slaves coming from subsaharan africa. Maybe if the plagues that ravaged a part of the islamic world in the 10th century were more violent this would solve the problem, but it's more likely that they'll just take slaves from africa to replace this lack of manpower.
The availability of coal in the islamic world can be seen in the east, especially in kurdistan and iran. Considering the abbassids controlled these regions for a very long time, they could have began a large scale exploitation of these coal mines, IF they knew where to find them and how to actually use the coal which was not seen as that useful in the medieval ages (if i remember correctly, coal was beginning to be really exploited in the late 18th century in Britain). So for that to happen, there needs to be a magical discovery of these mines and arab scholars genuinely interested by the many uses of this coal.