According to a new scientific study the global temperature does not rise or fall chaotically in the long run and should remain stable unless pushed by outside forces such as human activity.
Scientists at Duke University in the United States and NASA’s Jet Propulsion Laboratory examined how Earth cools itself down after a period of natural warming.
The new evidence, published in the Journal of Climate, contradicts the belief that long-term global warming occurs in an unpredictable manner, independently of external drivers such as human activity.
“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 author Patrick Brown, a PhD student at Duke’s Nicholas School of the Environment.
The study used global climate models and NASA satellite observations of Earth’s energy budget from the past 15 years.It found that a warming Earth was able to restore its temperature equilibrium through complex and seemingly paradoxical changes in the atmosphere and the way radiative heat was 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.
“Our analysis confirmed that the Planck Response plays a dominant role in restoring global temperature stability, but to our surprise we found that it tends to be overwhelmed locally by heat-trapping positive energy feedbacks related to changes in clouds, water vapour, and snow and ice,” Mr Brown said.
A more detailed investigation of the satellite observations and climate models helped the researchers finally reconcile what was happening globally versus locally.
“While global temperature tends to be stable due to the Planck Response, there are other important, previously less appreciated, mechanisms at work too,” said Dr Wenhong Li, assistant professor of climate at Duke.
These other mechanisms include a net release of energy over regions that are cooler during a natural, unforced warming event.
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.