The author concludes that if Earth’s atmosphere becomes significantly warmer, heavy downpours are likely to become more frequent. This is supported by a causal chain. A warm atmosphere leads to faster evaporation, which leads to rain clouds forming more quickly. A warm atmosphere also leads to more moisture in the atmosphere, which makes clouds larger. The larger, more quickly forming rain clouds result in heavier downpours. This is how heavy downpours are more likely if the atmosphere gets warmer.

The referenced text is offered as support for the conclusion. It’s part of the causal chain that shows how a warmer atmosphere can lead to more frequent heavy downpours.