Answer:
A global effect generally affects, as the term implies, the world as a whole, or at least a major part of the world, while a local effect would be just in a distinctive area.
For example, if the world is heating up due to CO2 emissions, it heats up in an global effect, resulting in the median temperature rising in all areas of the world. However, the world heating up may only mean a drought in distinctive areas that are typically already leaning towards the drier side (local effect), while the others receive a greater than usual volume of water due to rising temperatures.
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