When energy from the Sun reaches the Earth, it warms the atmosphere, land, and ocean and evaporates water. The movement of water from the ocean to the atmosphere to the land and back to the ocean—the water cycle—is fueled by energy from the Sun.
Changes in the energy cycle will ripple into the water cycle. As greenhouses gases retain more energy in the Earth system, the extra energy enhances the water cycle. An enhanced water cycle means more extreme weather events, particularly floods and droughts.
Terra and the water and energy cycle
Four of Terra’s five instruments record aspects of the water and energy cycles. Because these measurements are taken at the same time, they help scientists map out the connections between the land and ocean surface, water vapor, clouds, and energy.
Atmospheric water vapor and clouds
A warming climate will increase concentrations of water vapor in the atmosphere and may change clouds. MODIS measures both water vapor concentrations and cloud properties. The sensor can differentiate between liquid water and ice particles in a cloud. Both MISR and MODIS record cloud-top height, and CERES measures the amount of energy clouds reflect and radiate. Taken together, these measurements are helping define the relationship between clouds and energy and are tracking how clouds and water vapor change as climate changes.
Surface reflectance and energy
All things absorb and reflect energy from the Sun. Bright surfaces, like snow, ice, and clouds, reflect more energy than they absorb. Dark surfaces like a forest or the ocean absorb more energy. The absorbed energy heats the surface, and it radiates heat back into space. The CERES sensor records the amount of energy that is reflected from the Earth (reflected shortwave radiation) and the amount of energy that is radiated into space as heat (outgoing longwave radiation). ASTER, MODIS, and MISR measure the reflective properties of Earth’s varied surfaces. Taken together, these measurements help scientists understand how changes on Earth’s surface—replacing a dark forest with lighter-colored crops or exchanging white sea ice for a dark ocean—influence how energy is absorbed and reflected across the planet.