Millennium experiment with FAMOUS

We'd like to understand the climate changes since 800 AD (i.e., for just over a millennium). In addition to the post-industrial era, this period covers the Medieval Warm Period (~900-1300 AD) and Little Ice Age (~1300-1900AD) (see e.g. Medieval Warm Period on wikipedia). The anomalously warm and cold periods are probably caused by the variation of volcanic & solar activities plus the land use change, but the contribution of each component is not well understood.

In addition to satisfy the scientific and historical curiosity, this experiment is driven by the urgent need to refine the climate predictions. The climate models have so far been evolved to simulate the recent climate. The last "millennium" can provide an extra constraint to refine the models further.

However, both the driving force and the climate reconstructions over the pre-industrial era are based on the analysis of the natural archives of climate sensitive quantities, such as the growth of trees and seashells, and the changes of chemical, biological, and isotopic compositions in lake sediments and ice core samples. These "proxy" data are truly useful only when we fully explore the enormous range of the combined uncertainty.

To overcome this difficulty, we use a grand ensemble of a faster variant of the full-featured UKMO climate model, called FAMOUS (cf. www.FAMOUS.ac.uk). It runs about 10 times faster than the HadCM3L, which was used for the BBC experiment, because of reduced atmospheric resolution and increased ocean time-step. Therefore, the full 1200+ year simulation towards near future is only as expensive as the 160 year-long BBC experiment.

• Atmosphere: 3D GCM (5.0 x 7.5 degrees resolution, 11 levels).
• Ocean: 3D GCM (2.5 x 3.75 degrees resolution, 20 levels).
• Sea Ice: simple thermodynamic model with drift.
• Land: vegetation and hydrological cycle.

In addition to the perturbations in internal physics parameters and initial condition, this experiment requires a large number of forcing perturbations to deal with the large uncertainty in the historical forcings.

To reduce the CPU time further, prallelization by domain decomposition has been tested. If everything goes well, this experiment will be the first CPDN experiment to take full advantage of multi-core and multi-CPU machines. For the initial release, however, we decided not to distribute the parallel version because we need more preparation time for packaging.

The Millennium experiment has been primarily funded by European Comission through Framework 6 project European Climate of the last Millennium (http://www.millenniumproject.net/). While the modelling experiment is performed, the Millennium partners have been working to quantify and reduce the uncertainties in the climate "proxy" information by collecting and analysing more climate records. However, we are now looking for more supporters as the EC project will finish at the end of June 2010.

This experiment has been designed in AOPP, Oxford through discussion in the paleo-climate community in Europe and beyond; It is currently only available at the beta test site. Stay tuned for the official launch. Contact: hiro@cpdn.org