Earth has three main climate zones because of the differences in latitude and

Distribution of sunlight.

Explanation:

The three major climatic zones of the earth are coldest polar zone, warm and humid tropical zone, and the moderate temperate zone. These zones are classified depending on intensity of rainfall and temperature of these places. Due to differences in latitude leading to difference in distribution of sunlight globally, that's what leads to categorization of these three main climatic zones.

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