Right answer: atmosphere
When the Sun radiation comes to the Earth, a part is absorbed and the other is reflected by the clouds in the atmosphere and the Earth’s surface.
This is called albedo, which is the percentage of radiation that any surface reflects with respect to the incident radiation. Clear surfaces have higher albedo values than dark ones, and bright ones more than matt ones. In this sense, Earth’s average albedo is about 0.3. In other words, about 30 percent of solar radiation that comes to the Earth is reflected back into space and 70 percent is absorbed.
Therefore:
Much of the sun’s radiation is reflected back into space by the earth’s atmosphere