Desiccating salt ponds in France. A new study provides deeper insight insight into why evaporation will likely increase under a warming climate. Credit: Loïc Lagarde, CC BY-NC-ND 2.0
Source: Journal of Geophysical Research: Atmospheres

Bumping up atmospheric carbon dioxide levels causes temperatures to rise across Earth’s surface. This direct climate correlation is well established, but measuring carbon dioxide (CO2) levels is not enough to build accurate climate models. Making precise predictions of temperature and weather patterns around the globe requires models that incorporate what scientists call feedbacks, an array of secondary changes that can amplify or diminish climate change.

As Earth warms, it radiates heat back into space, creating a negative feedback. But extra moisture in the air acts to trap outgoing radiation, further increasing the temperature. When the Earth’s atmosphere absorbs more energy than it reflects or releases, the planet warms and vice versa. Taken together, these processes direct radiative forcing, or the overall balance of energy, to keep energy gains and losses in equilibrium.

Traditionally, scientists have studied the processes behind these gains and losses in energy where the action happens—at the top of Earth’s atmosphere. There, the feedback processes at work to keep the amount of energy lost and gained in equilibrium determine global temperatures.

Previous research has shown that these same processes operate at the planet’s surface and can drive fluctuations in surface temperatures, the water cycle, and weather patterns that have direct impacts on humans and the environment. But uncertainties in the strength and structure of surface energy responses remained. Recently, Colman aimed to create a more comprehensive picture of the radiative feedbacks operating at Earth’s surface when CO2 levels steeply climb.

Colman used a global circulation model to examine surface radiation changes under scenarios in which CO2 was doubled or quadrupled. He found that changes in cloud formation, relative humidity, and latent heat flux all contributed to a rapid response in surface energy. Ultimately, the study showed that as Earth’s surface warms, extra radiation trapping from increased water vapor will exceed direct surface radiative cooling, driving a net increase in evaporation.

Overall, his findings indicate that feedback processes at Earth’s surface differ widely from those at the top of Earth’s atmosphere, where they’re commonly measured. (Journal of Geophysical Research: Atmospheres, doi:10.1002/2014JD022896, 2015)

—Eric Betz, Freelance Writer

Citation: Betz, E. (2105), Surface climate processes keep Earth’s energy balance in check, Eos, 96, doi:10.1029/2015EO034771. Published on 31 August 2015.

Text © 2015. The authors. CC BY-NC 3.0
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