Understanding the past climate evolution helps to improve our assessment of how the climate may evolve in the future. Internal climate variability and naturally forced climate variability limit our certainty in climate projections in addition to the uncertainties of future societal and economic scenarios.
Two large research initiatives are presently studying the climate of the last thousand to two thousand years. The Past Global Changes (PAGES) 2K network tries to incorporate palaeo-observations into reconstructions of important climatic parameters for individual regions and over the last 2000 years. On the other hand, the third phase of the Palaeoclimate Intercomparison Project (PMIP3) included simulations for the period 850 to 1850 CE.
Madrid in early November was the place for both initiatives to meet for discussions on comparative analyses of both approaches (i.e. simulations and reconstructions) to further the understanding of physical mechanisms, and to link past and future climate evolution. This could help to constrain the uncertainty in future climate projections. The meeting particularly emphasised the continental/regional scales.
Review talks introduced the regional reconstructions of the PAGES2K consortium and the past1000-simulations from the PMIP3-initiative. These talks further presented previous efforts in comparing simulations and reconstructions and tried to extend the scope to not yet fully employed methodologies like data assimilation, regional modelling, and detection and attribution. In addition, previous studies on the identification of extreme events and modes of climate variability were reviewed.
Subsequently, three working groups presented initial results on the PMIP3-simulation-reconstruction comparison focussed on the PAGES2K regions, on circulation modes, and on best practices and perspectives in model-data-comparison. Nick McKay adapted the analyses on the temperature response to the assumed forcing perturbations presented in the IPCC AR5 to the PAGES2K regions. Results by Joëlle Gergis and colleagues provided an initial perspective on the comparison of southern hemispheric climate modes, whereas Davide Zanchettin investigated the behavior of the Pacific North America (PNA) pattern in the PMIP3 simulations and provided insight into pseudo-reconstructions of this mode. Johann Jungclaus highlighted the big challenge of comparing marine proxies with simulations. Subsequently Mike Evans emphasized how direct comparison of forward modelled pseudo-proxies and real proxies provides a new perspective for palaeoclimate research. Results by Schurer and Hegerl on detection and attribution and Moberg and Hind on innovative model-data-comparison-metrics displayed a motivating similarity in identifying regions with high model-data-consistency. Beyond these mentioned analyses various other preliminary results were presented and provided perspectives for upcoming products from the workshop.
Based on these preliminary three working groups, three breakout groups discussed possible short-, and mid-term products and products based on the comparison of modes of climate variability. This resulted in plans for a synthesis of methods applied to the PAGES2K regions, a discussion of climate modes and a mid-term best practises paper.
Further discussions highlighted the interest in using the data-model-comparison to study the climatic effect of large volcanic eruptions, and the necessity to compare different reconstruction techniques based on pseudo-proxy-studies and based on forward modelled proxy-series. Jason Smerdon suggested establishing a data-model intercomparison project (DMIP) for the last two millennia.
An outreach event accompanied the workshop. It was embedded in the 13th week of science in Madrid and asked “Science and society facing climate change, do we understand each other?”. A general introductory talk by Jason Smerdon provided a short presentation on well founded and uncertain aspects of climate change science which was followed by a discussion between the workshop participants and the interested public. The discussion touched on topics such as the IPCC AR5, the current hiatus-phase, the problems of communicating science publically, the sometimes possibly falsely balanced nature of the climate change debate in the mainstream media, and more. The interactions with the public resulted in lengthy discussions among the workshop participants about business interests in climate change research, the possibility and the quality of climate predictions, and the problem of overconfidence.
Reactions by the public after the outreach event suggests a successful meeting between the general public and science. This success is also mirrored by the workshop as a whole. The participants agreed on the intensity of the meeting, the seriousness of the discussions, and the inspiring prospect of the future plans.
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The above is obviously a rather superficial depiction of the workshop, which tries not to tread on anybody’s toes. For more detailed discussions… let’s hope that some other participants chime in.
14ter Stock 
An alternative link to the “current hiatus phase” could be this one.
Is there any reason why the modellers are studying just 1000 years and the paleo reconstructions are for 2000 years? Would sound worthwhile to coordinate this.
In the same week, there was a EUMETNET meeting on climate data near Madrid. So I happen to have met some people of your meeting on Saturday. Including some locals, that guided us to the best food available. :-d
One of them claimed, after asking about the divergence, that it would be good to remove tree rings with problems after 1960 from the entire dataset. Is that the general opinion of the community? Or one of the toes?
So, WP thought Victor’s comment was spam.
As far as I can tell there are two reasons for the different foci (800-1850 vs 0-2000). I think the 2K focus is to some extent motivated by it being the next “frontier”. However, as the Nature Geoscience consortium paper highlights: having a goal doesn’t imply one is able to achieve it.
The modellers also would like to do 2K simulations (and some did that already) but the volcanic forcing data was insufficient for the early first millennium CE when PMIP3 was designed – and still is. If I remember correctly, some also argue: why stop at 2K, shouldn’t we do a transient holocene (6K) simulation?
I am not a specialist on the divergence problem. Wilson, Evans, Anchukaitis, Cook and others are probably better contacts for that question. My impression is that the D’Arrigo et al. (2008) paper is still the best reference.