Because hot air come .

because the sun comes to the nearest position of the earth which half hemisphere you live.

I do agree with Ethan, because of the sun

i suppose you should go to a library and ask a encyclopedia

yes dear it is really strang that in summer weather always hot and why..no body knows{after all who can understands the nature of nature}

Because it's summer. Summer should be hot!

o,no no~
my teacher just said ,the sun is farthest from the earth in summer,but the rotation of the earth is slowest in the summer。so there is more hot from sun~

100% has EVERYTHING to do with with the rotation of the Earth, the distance from the Sun and the angle at which it hits. I studied astrophysics in university, if anyone has any questions about space or physics in general, feel free to ask (though i don't promise to have the answer...I would love to give it a go).