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A new Duke University study based on 1,000 years of actual temperature records suggests that global warming is not progressing as quickly as it would under the worst-case emissions scenarios set forward by the Intergovernmental Panel on Climate Change (IPCC).
Best estimates and likely ranges for global average surface air warming below for six SRES emissions marker scenarios are given in this assessment and are shown in Table SPM.3. For example, the best estimate for the low scenario (B1) is 1.8°C (likely range is 1.1°C to 2.9°C), and the best estimate for the high scenario (A1FI) is 4.0°C (likely range is 2.4°C to 6.4°C). Although these projections are broadly consistent with the span quoted in the TAR (1.4°C to 5.8°C), they are not directly comparable. Image below courtesy of the IPCC.
To no surprise, this latest study, led by Patrick T. Brown, a doctoral student in climatology at Duke University’s Nicholas School of the Environment and Wenhong Li, assistant professor of climate at Duke showed that natural variability in surface temperatures, which are caused by interactions between the ocean, atmosphere and other natural factors can account for observed changes in recent rates of warming from decade to decade.
To test how accurate climate models are at accounting for variations in the rate of warming, Brown and Li, along with colleagues from San Jose State University and the USDA, created a new statistical model based on reconstructed empirical records of surface temperatures over the last 1,000 years. (via Duke Environment)
The research team found that the IPCC climate models largely get the "big picture" right but underestimate magnitude of natural decade-to-decade climate "wiggles", according to Brown.
Image courtesy of NASA GISS.
Brown explains that some of these "wiggles" have been big enough to have accounted for a reasonable portion of the accelerated warming that went on between 1975-2000, but also the reduced rate of warming from 2002-2013.
Other key excerpts from the Duke Environment story.....
“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 Li. “Statistically, it’s pretty unlikely that an 11-year hiatus in warming, like the one we saw at the start of this century, would occur if the underlying human-caused warming was progressing at a rate as fast as the most severe IPCC projections,” Brown said. “Hiatus periods of 11 years or longer are more likely to occur under a middle-of-the-road scenario.”
Under the IPCC’s middle-of-the-road scenario, there was a 70 percent likelihood that at least one hiatus lasting 11 years or longer would occur between 1993 and 2050, Brown said. “That matches up well with what we’re seeing.”
This study has been published in the journal Scientific Reports.
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