A new study suggests global warming is progressing at a moderate rate and has not reached a level of "worst case scenario."
The analysis looked at 1,000 years of temperature records and found the temperature changes have not been as dramatic as what was predicted under the most severe emissions scenarios outlined by the Intergovernmental Panel on Climate Change (IPCC), Duke University reported.
"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 study shows natural variability in surface temperatures can account for the observed warming that has occurred from decade to decade. These "climate wiggles" are believed to be able to slow or speed up the rate of warming and could even have an influence on greenhouse gas concentrations. These factors could interfere with the accuracy of climate models if not completely understood and taken into account.
"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.
To test the accuracy of climate models, the researchers created a new statistical model based on empirical data on surface temperatures over the past millennium.
"By comparing our model against theirs, we found that climate models largely get the 'big picture' right but seem to underestimate the magnitude of natural decade-to-decade climate wiggles," Brown said. "Our model shows these wiggles can be big enough that they could have accounted for a reasonable portion of the accelerated warming we experienced from 1975 to 2000, as well as the reduced rate in warming that occurred from 2002 to 2011."
The research also revealed that an 11-year warming hiatus like we saw at the start of the century is statistically unlikely if warming is progressing at the rate of the most severe IPCC projections but is more plausible under a middle-of-the road scenario.
"Our analysis clearly shows that we shouldn't expect the observed rates of warming to be constant. They can and do change," Li stressed.
The findings were published in a recent edition of the journal Scientific Reports.
