By assessing how planet Earth cools down after a natural warming period, researchers have confirmed that the world's temperature doesn't rise or fall erratically in the long term unless acted upon by an external driver.

In a study published in the Journal of Climate, researchers from NASA's Jet Propulsion Laboratory and Duke University provided evidence countering belief that global warming skeptics hold about the long-term rise in temperature occurring unpredictably and independently of external forces like human activities.

"This underscores that large, sustained changes in global temperature like those observed over the last century require drivers such as increased greenhouse gas concentrations," says Duke University's Patrick Brown, the study's lead author. According to him, natural cycles involving climate alone cannot sufficiently explain changes in temperature.

Examining satellite observations made of Earth's energy budget and global climate models from the last 15 years, the researchers found that a warming planet is capable of restoring temperature equilibrium through complex and atmospheric changes and radiative heat transportation that appear paradoxical.

Earth's ability to stabilize its temperature is attributed to what is called the Planck Response, a phenomenon characterized by a large growth in the level of infrared energy emitted by the planet as it warms. As some kind of safety valve, the Plank Response results in a negative radiative feedback that lets accumulated heat to be released via the atmosphere's top and into space.

However, according to the study, things are not as simple as that.

Brown says their findings prove that the Planck Response has a big part in keeping Earth's temperature stable but the phenomenon has a tendency of being overwhelmed locally by changes in ice, snow, water vapor and clouds that are related to positive energy feedbacks that trap heat.

While the Planck Response does stabilize global temperature, other factors are also at play and that are just as important but not as known. These other factors include a net release of energy across cooler regions during unforced, natural warming events and energy transport from tropic Pacific to polar and continental locations where the Planck Response can override local positive heat-trapping events.

The study received funding support from NASA and the National Science Foundation. Other authors include Hui Su, Jonathan Jiang and Wenhong Li.

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