Earth's temperature is greatly influenced by the amount of sunlight reaching the earth, but recent studies have shown that the sun's solar output has decreased in recent decades. The evidence to support this claim is that the troposphere (the innermost layer of the atmosphere) has become warmer while the mesosphere (the third layer of the atmosphere) has become colder. If the sun were the only cause of global warming, the atmosphere would get warmer from top to bottom, but this is not the case because it gets warmer from bottom to top. The greenhouse effect also plays a key role in the Earth's climate. The greenhouse effect occurs when solar radiation is absorbed by the