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Long-term global warming not driven naturally

Study debunks argument that warming is driven by natural factors

Date:
February 1, 2016
Source:
Duke University
Summary:
By examining how Earth restores equilibrium after periods of natural warming, a new study reinforces that long-term global temperature does not evolve chaotically but remains stable unless pushed by external factors. Large, sustained changes in global temperature, like those observed over the last century, cannot occur without drivers such as increased greenhouse gas concentrations. Estimates of natural climate cycles alone are insufficient to explain such changes.
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By examining how Earth cools itself back down after a period of natural warming, a study by scientists at Duke University and NASA's Jet Propulsion Laboratory confirms that global temperature does not rise or fall chaotically in the long run. Unless pushed by outside forces, temperature should remain stable.

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 author Patrick Brown, a PhD student at Duke's Nicholas School of the Environment. Natural climate cycles alone are insufficient to explain such changes, he said.

Brown and his colleagues published their peer-reviewed research Feb. 1 in the Journal of Climate.

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

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

The new Duke-NASA research, however, shows it's not as simple as that.

"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 vapor, and snow and ice," Brown said. "This initially suggested that the climate system might be able to create large, sustained changes in temperature all by itself."

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 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. 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 emphasizes 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 said.


Story Source:

Materials provided by Duke University. Note: Content may be edited for style and length.


Journal Reference:

  1. Patrick T. Brown, Wenhong Li, Jonathan H. Jiang, Hui Su. Unforced Surface Air Temperature Variability and Its Contrasting Relationship with the Atmospheric TOA Energy Flux at Local and Global Spatial Scales. Journal of Climate, February 2016 DOI: 10.1175/JCLI-D-15-0384

Cite This Page:

Duke University. "Long-term global warming not driven naturally." ScienceDaily. ScienceDaily, 1 February 2016. <www.sciencedaily.com/releases/2016/02/160201215946.htm>.
Duke University. (2016, February 1). Long-term global warming not driven naturally. ScienceDaily. Retrieved March 28, 2024 from www.sciencedaily.com/releases/2016/02/160201215946.htm
Duke University. "Long-term global warming not driven naturally." ScienceDaily. www.sciencedaily.com/releases/2016/02/160201215946.htm (accessed March 28, 2024).

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