Global warming not driven by natural forces: Study

The new evidence may finally help put the chill on skeptics' belief that long-term global warming occurs in an unpredictable manner, independently of external drivers such as human impacts.

"This underscores that large, sustained changes in global temperature like those observed over the last century require drivers such as increased greenhouse gas concentrations," said lead study author Patrick Brown from Duke University in North Carolina, US.

Natural climate cycles alone are insufficient to explain such changes, he said.

The findings appeared in the Journal of Climate.

Using global climate models and NASA satellite observations of Earth's energy budget from the last 15 years, the researchers found that a warming Earth is able to restore its temperature equilibrium through complex changes in the atmosphere and the way radiative heat is transported.

Scientists have long attributed this stabilisation to a phenomenon known as the Planck Response, a large increase in infrared energy that Earth emits as it warms.

"While global temperature tends to be stable due to the Planck Response, there are other important, previously less appreciated, mechanisms at work too," Wenhong Li, assistant professor of climate at Duke University, noted.

These other mechanisms include a net release of energy over regions that are cooler during a natural, unforced warming event.

And there can be a transport of energy from the tropical Pacific to continental and polar regions where the Planck Response overwhelms positive, heat-trapping local effects.

"This emphasises the importance of large-scale energy transport and atmospheric circulation changes in restoring Earth's global temperature equilibrium after a natural, unforced warming event," Li explained.