A new study based on 1,000 years of temperature records suggests global warming is not progressing as fast as it would under the most severe emissions scenarios outlined by the Intergovernmental Panel on Climate Change (IPCC). "Based on our analysis, a middle-of-the-road warming scenario is more likely, at least for now," said Patrick T. Brown, a doctoral student in climatology at Duke University's Nicholas School of the Environment. "But this could change."

The Duke-led study shows that natural variability in surface temperatures -- caused by interactions between the ocean and atmosphere, and other natural factors -- can account for observed changes in the recent rates of warming from decade to decade.

The researchers say these "climate wiggles" can slow or speed the rate of warming from decade to decade, and accentuate or offset the effects of increases in greenhouse gas concentrations. If not properly explained and accounted for, they may skew the reliability of climate models and lead to over-interpretation of short-term temperature trends.

The research, published today in the peer-reviewed journal Scientific Reports, uses empirical data, rather than the more commonly used climate models, to estimate decade-to-decade variability.

"At any given time, we could start warming at a faster rate if greenhouse gas concentrations in the atmosphere increase without any offsetting changes in aerosol concentrations or natural variability," said Wenhong Li, assistant professor of climate at Duke, who conducted the study with Brown.

The team examined whether climate models, such as those used by the IPCC, accurately account for natural chaotic variability that can occur in the rate of global warming as a result of interactions between the ocean and atmosphere, and other natural factors.