The greenhouse effect impacts Earth primarily by allowing for people to inhabit it. The greenhouse effect is a natural process that warms the Earth's surface. When the sun's energy reaches the Earth, some of it is reflected back to space and the rest is absorbed, warming the planet. The Earth then radiates this energy back into the atmosphere as infrared radiation. Greenhouse gases in the atmosphere (such as carbon dioxide, methane, and water vapor) trap some of this outgoing infrared radiation, preventing it from escaping back into space. This process helps to maintain a stable climate and keeps the Earth warm enough to support life.
While oceans and land do warm at different rates due to various factors, and the greenhouse effect does contribute to the overall climate system that influences seasons, the most direct and critical impact is indeed that it allows for the conditions necessary for human and other life to thrive on Earth.