What causes summer to be so warm?

Answer 1

If Earth's axis was not tilted, there would be no seasons. The seasons occur because the axis on which Earth turns is tilted with respect to the plane of Earth's orbit around the Sun. The North Pole is tilted toward the Sun for half of the year, and the South Pole is tilted toward the Sun for the other half of the year. The hemisphere that is tilted toward the Sun has a longer day, receives more of the Sun's rays, and receives them more directly than the hemisphere tilted away from the Sun. These conditions result in the season called summer.

Answer 2

Summer, as with all seasonal variations, is due to the tilt of the Earth's axis with respect to its orbit around the Sun. The relative angle of the Earth to the Sun causes an increase in the number of daylight hours, and a more vertical angle of sunlight, and hence warmer temperatures. As the Earth orbits the sun, the midpoint of the sunlit area moves from the Tropic of Cancer (23° 26′ 22″ N) to the Tropic of Capricorn (23°26′ 22″ S) and back again (only directly over the Equator twice a year). This causes more solar radiation to reach the northern or Southern Hemisphere. Longer days and summer for the Northern Hemisphere last from June to August. Longer days and summer for the Southern Hemisphere last from December to February.
Unlike most popular beliefs the distance from the sun has little to do with temperature

In June the northern hemisphere is tilted toward the sun and the southern hemisphere is tilted away, thereby causing winter in that hemisphere. This is reversed in December.

Answer 3

Boom boom --- however summer is hot because it is when we are closer to the sun than usual