Large bodies of water will impact the temperature by releasing energy slowly and absorbing heat from the Sun, which cools areas that are near large bodies of water and moderates the Earth's temperature. The process begins with with the Sun's energy and the radiation that comes off of the Earth's surface.
The Earth absorbs 50 percent of the Sun's energy before releasing it into the atmosphere. This means that the Earth and the Earth's surface material play a large role in the temperature of the air in each location around the Earth.
The materials of the Earth absorb energy differently from one another. Some of the materials easily absorb energy while others reflect energy easily. Animals and plants, which are organic materials, absorb energy better than an open desert or stretch of barren land. This is why the temperatures in forests are cooler than the temperatures found in deserts. The trees help to absorb some of the energy from the Sun.
Water is one of the best materials on the Earth for absorbing the Sun's energy. Water also has the ability to store the Sun's energy for a long period of time before releasing it. Furthermore, large bodies of water also release energy slowly. This is why the cities and towns nearest a large body of water often have more mild climates.