NASA has granted a small team of University of Arizona researchers $3.46 million over 11 years to help monitor Earth's radiation budget, which is the balance between the absorbed solar energy on the surface and the infrared radiation Earth emits back into space. When Earth emits less than it absorbs, it leads to global warming.

The grant is part of the larger $150 million Libera mission that will orbit Earth to measure Earth's energy. Libera will launch in 2027 to continue the work of NASA's outgoing mission CERES, short for Clouds and the Earth's Radiant Energy System. Ceres, the Roman goddess of agriculture, is Libera's mother in Roman mythology.

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The UArizona team that is part of the Libera mission is led by professors Xiquan Dong and Baike Xi in the Department of Hydrology and Atmospheric Sciences. Dong and Xi have been involved in the CERES project since 1996. Libera is NASA's first Earth Venture Continuity mission, a new type of investigation under the larger Earth Venture mission class. Continuity missions focus on maintaining continuous measurements important to the Earth science community.

The data Libera collects will be made publicly available.

"This is the latest example of how our researchers are creating solutions to tackle the world's biggest challenges," said University of Arizona President Robert C. Robbins. "Studying climate change requires us to think beyond human time scales. Thirty years might seem like a long time to us, but for climate studies, 30 years is the baseline. The Libera mission and our participation in it will continue NASA's 20-year legacy of Earth radiation budget measurements starting with CERES. I am proud to see our longstanding history of collaboration with NASA continued in this way."

Libera will measure Earth's energy – in watts per square meter – looking down from space, through the atmosphere to the surface. The UArizona team will use surface measurements and a computer model to stitch together a global map of surface radiation. By subtracting the surface energy from the measurements taken from the top of the atmosphere, the Libera team can isolate the amount of energy trapped in the atmosphere.

"Think of the sun like a flashlight. If you're pointing it straight down, it's bright in a small area," Dong said. "When you shine it at an angle, the light covers a larger area, but it's not as bright; the watts per square meter decrease."

Solar radiation works the same way: The amount of light and energy the sun emits is always the same, but as the sun's angle in the sky changes, so does the amount of energy Earth receives. The energy on Earth gradually increases as the sun rises, peaks around noon and tapers as the sun gets lower in the sky until it sets.

This is also why the equator is warmer than the poles. The sun at the equator is like a flashlight shining straight down, while at the poles, the same light is distributed over a larger area.

Atmospheric energy drives atmospheric circulation, so this research will also allow scientists to understand how energy is transported from the equator to the poles. This information has implications for how climate change is related to sea ice melt and sea level rise, as most extra energy moves from the tropics to polar regions.

"We get more energy at the equator and less at the poles, but the atmosphere circulation transports energy from the equator or poles. If it didn't, tropical regions would get too warm, and the poles would freeze out. So, there's a heat balance and transport of energy," Dong said. "We want to study how much energy is transported from the regions near the equator to the polar regions and how that energy transport contributes to arctic sea ice melt."