Final answer:
About 29.3% of the sun's incoming shortwave radiation is reflected back to space, largely due to Earth's albedo from reflective surfaces such as clouds and snow.
Step-by-step explanation:
Approximately 29.3% of all incoming shortwave (SW) radiation from the sun is reflected back to space. This reflection occurs due to the Earth's albedo, which is primarily contributed to by clouds, snow, and other bright surfaces that do not absorb light but rather reflect it back into space. Of the 1360 W/m² of solar power arriving at Earth, known as the solar constant, this means that around 399.48 W/m² is reflected, with the remaining 960 W/m² absorbed by the planet, as averaged over the entire surface area of the Earth.