Final answer:
Insolation refers to incoming solar radiation and is primarily determined by solar radiation, which is the most significant factor in the amount of energy reaching the Earth's surface to drive the climate system. The most appropriate correct option is B.
Step-by-step explanation:
Insolation is an acronym for incoming solar radiation. It is the amount of solar energy that reaches the Earth's surface and is the primary energy input for the Earth's climate system. The correct answer to the question regarding what largely determines insolation is b) Solar radiation. Atmospheric pressure, humidity levels, and ocean currents play roles in the climate system but do not determine the amount of solar energy that reaches the Earth. About 70% of the incoming solar energy is absorbed by the atmosphere and land, while the rest is reflected back into space, primarily by clouds and ice. The absorbed energy on the surface is used in various ways, including evaporating water which starts the hydrological cycle, driving winds, enabling photosynthesis, and influencing weather patterns by redistributing heat via the atmosphere and ocean currents.
Changes in solar intensity are also crucial as they can cause temperature fluctuations on Earth, which is evidenced by historical climate events such as the Little Ice Age. Thus, solar radiation is essential for weather and climate, and understanding insolation is key to comprehending Earth's climate system.