Read the passage and answer the question.
Passage: Urban farming is gaining popularity as cities grow more crowded.
Growing food in rooftop gardens, vertical farms, and community plots helps reduce the distance food must travel from farm to table.
Supporters argue this lowers carbon emissions and improves access to fresh produce.
However, critics note that urban farms require significant investment in infrastructure and may not produce enough food to meaningfully supplement city supplies.
What is the main idea of this passage?