How do human activities contribute to the greenhouse effect?

Human activities contribute to the greenhouse effect primarily through the release of significant amounts of greenhouse gases, such as carbon dioxide, methane, and nitrous oxide. These gases are produced from various sources, including the burning of fossil fuels for energy and transportation, industrial processes, agricultural practices, and deforestation.

When humans engage in activities that emit these gases, they enter the atmosphere and trap heat, leading to an increase in Earth's average temperature. This is known as the greenhouse effect, which is essential for maintaining the planet’s warmth but is intensified by the excess amount of greenhouse gases produced through human activity.

In contrast, other options like decreasing the use of fossil fuels, increasing tree planting efforts, and reducing industrial emissions are actions that can help mitigate the greenhouse effect rather than contribute to it. Therefore, the correct answer highlights the primary way human activity exacerbates this environmental challenge.