Pages 2k has a new Nature paper called Consistent multidecadal variability in global temperature reconstructions and simulations over the Common Era. What they do is present 2,000-year-long global mean temperature reconstructions using seven different statistical methods that draw from a global collection of temperature-sensitive palaeoclimate records which display synchronous multidecadal temperature fluctuations that are coherent with one another.The top panel of the figure on the left shows the temperature reconstruction for the last 2000 years, indicating a general cooling trend prior to 1850 and the subsequent warming that continues today. The lower panel shows the 30 to 200 year bandpass-filtered ensemble, showing the multi-decadal variability, which is consistent across all the statistical methods. What I found interesting about the paper is that they then did a detection and attribution analysis to try and explain the pre-industrial multidecadal variability. The figure on the right shows that a substantial portion of the variability can be explained as being due to changes in external forcings, in particular volcanic aerosol forcing. In addition, the residual can be used to estimate the magnitude of the unforced/internal variability. This is consistent with the variability in pre-industrial control simulations, which suggests that models are probably not under-estimating unforced/internal variability.
The paper also considers 51-year running trends and they find that a majority of the ensemble members show the largest 51-year trend occurring in the twentieth century, indicating that the modern warming trend is outside the range of pre-industrial variability.
So, this looks like an interesting paper that illustrates that pre-industrial variability is a combination of forced (mostly volcanoes), and unforced variability that has a magnitude that is consistent with pre-industrial control simulations. It also demonstrates that the modern warming period is warming at a rate that is outside the range of pre-industrial variability. None of this is really a surprise, but it does seem to be a nice way to constrain unforced variability and illustrate that what we’re undergoing today is certainly unusual.