In The Name of Allaah, The Most Merciful The Bestower of Mercy
Allaah (The Most High) said:
ظَهَرَ ٱلۡفَسَادُ فِى ٱلۡبَرِّ وَٱلۡبَحۡرِ بِمَا كَسَبَتۡ أَيۡدِى ٱلنَّاسِ لِيُذِيقَهُم بَعۡضَ ٱلَّذِى عَمِلُواْ لَعَلَّهُمۡ يَرۡجِعُونَ
Evil (sins and disobedience of Allah, etc.) has appeared on land and sea because of what the hands of men have earned. [30:41]
Imaam Ibnul Qayyim (rahimahullaah) said:
This ayah was revealed regarding the state of affairs of the world- the relationship between it and the events that occur. You see how the occurrence of those evil actions and defects (of the people) affects the harvest, vegetation and the animals in every era, and the manner in which those evil (affairs) necessitates other evils. And whenever the people initiate oppression and wickedness, their Lord (The Blessed and Most High) brings about- from those evils and defects (of theirs)- deficiencies and harm in their nourishments, fruits, atmospheres, bodies, physical natures, outward appearances and manners, as a justification for their deeds, acts of oppression and wickedness.
Indeed, the grains of wheat and other than them used to be bigger than what they are today, just as the blessing in them was greater. Imaam Ahmad (rahimahullaah) narrated with his chain of transmission that a packet was found in one of the treasury departments of Bani Umayyah in which there was a grain nearly the size of a date. This grain was grown and harvested during an era of justice.
The majority of the illnesses and the general evil affairs are remnants of the punishment afflicted upon the people of the previous nations; then there remained from that what remains, as a surprise punishment against those who remain upon the (evil) deeds of those previous nations. This is a just judgement and just decree. And indeed the Prophet (sallal-laahu-alayhi-wasallam) has indicated to this in his statement concerning plagues, that it is a remnant of an affliction or punishment that was sent by Allaah to the Children of Israa’eel.
[Source:Badaa’i-ul At-Tafseer Al-Jaami Limaa Fassarahu Al-Imaam Ibnu Qayyim Al-Jawziyyah: page: 313: Vol:2..abridged and slightly paraphrased]