Study warns global warming not driven by natural forces

Study warns global warming not driven by natural forces

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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.
City-heat-global-warmingThe 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.

Patrick-Brown-PhD-student-environment-Duke-UniversityNatural climate cycles alone are insufficient to explain such changes, he said.

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.

warmer-Europe-seasons-EUActing as a safety valve of sorts, this response creates a negative radiative feedback that allows more of the accumulating heat to be released into space through the top of the atmosphere.

“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.

US-storms-cars-traffic-snow“This initially suggested that the climate system might be able to create large, sustained changes in temperature all by itself,” he said.

A more detailed investigation of the satellite observations and climate models helped the researchers finally reconcile what was happening globally versus locally.

Dr-Wenhong Li-assistant-professor-climate-Duke-University“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.

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