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(Refreshments served)Time: 1:30–2:30 pm
The climate of the Common Era before the industrial period is of great policy interest because it provides a baseline for understanding the natural climate variability on which our current anthropogenic change is superimposed. A relative wealth of information from various proxies allows for reasonably high spatial and temporal reconstructions of past climate variables. Separating the responses associated with internal versus forced variability can only be truly done by using numerical models. Most CMIP5 simulations for the period 850-1850CE only include one realization for a given model. Yet, in light of the relatively small forcings of solar, volcanic, greenhouse gases, and land use changes, one realization is not adequate except at larger space and time scales. In addition, the data cannot easily provide an attribution to a single forcing nor verify interpretations of the thermodynamic and dynamic mechanisms that explain the regional responses suggested in the proxy records.
In this talk, I will first discuss a few examples where climate changes recorded by proxies have been linked to solar output changes. I will review our previous modeling of the last millennium with the CSM/CCSM before describing the results from our new of community project to produce a large modeling ensemble for the period 850-2005CE. At the core of this experiment is an 8-member ensemble using the CESM-CAM5 coupled climate model at a resolution of 2° for the atmosphere and 1° for the ocean and with the PMIP3/CMIP5 full forcings (solar variability, orbital changes, volcanic eruptions, greenhouse gases, and land use). Ensemble experiments for each of these forcings individually are being evaluated to separate out their roles in explaining the model responses. As this project is ongoing, I will finish with an outline of our next steps.