Open Thread - Science Division

Some things which caught Eli's Eye, but, it being summer, only a few comments from the meadow are likely.

- A really interesting paper in Climate of the Past Discussions, a collaboration between the PAGES2K (turbo proxy reconstructions) and PIMP3  PMIP3 (modeling of the past) groups "Continental-scale temperature variability in PMIP3 simulations and PAGES 2k regional temperature reconstructions over the past millennium" which will not bring smiles in certain quarters.  Warning, it is another Hansen, et al seventy pager.  To quote from the abstract:

Here, the recent set of temperature reconstructions at the continental scale generated by the PAGES 2k project and the collection of state-of-the-art model simulations driven by realistic external forcings following the PMIP3 protocol are jointly analysed. The first aim is to estimate the consistency between model results and reconstructions for each continental-scale region over time and frequency domains. Secondly, the links between regions are investigated to determine whether reconstructed global-scale covariability patterns are similar to those identified in model simulations. The third aim is to assess the role of external forcings in the observed temperature variations. From a large set of analyses, we conclude that models are in relatively good agreement with temperature reconstructions for Northern Hemisphere regions, particularly in the Arctic. This is likely due to the relatively large amplitude of the externally forced response across northern and high latitudes regions, which results in a clearly detectable signature in both reconstructions and simulations. Conversely, models disagree strongly with the reconstructions in the Southern Hemisphere.

It is not clear whether one should trust the models or the reconstructions, if for no other reason than there are fewer proxy's from the South.  Get busy.

- And indeed some have.  In a related development Sigi and about twenty others, settle the issue of when volcanic  eruptions took place in the past by aligning ice core proxy records.   "Timing and climate forcings of volcanic eruptions for the past 2,500 years"(no open source at the moment) provides a huge lever for the paleoclimate types to move their work forward on both the physical and historical levels.

Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.

Variation in timing smears out and diminishes the effects of large eruptions and disappears that of smaller ones.  This new work, and aligning it with PAGES2K certainly requires a re-evaluation of Maas and Portman who in 1989 concluded that only the effects of the larges eruptions could be seen in the climate record records.

IEHO comparison of PAGES2K regional reconstructions using the Sigi et al chronology will allow major progress in identifying the sites of the smaller (and some of the larger) eruptions as well as refining estimates of global and regional volcanic forcings.  This, in turn will drive progress in paleoclimate modeling as well as estimation of immediate and equilibrium climate sensitivity.

Consider this an open thread.