final_program_abstracts[1]

11 IMSC Session Program
Calibrating pseudoproxies
Tuesday - Poster Session 3
Peter Green
The performance of a palaeoclimate reconstruction method can be tested in a
pseudoproxy experiment. The method is used to reconstruct a model climate from
simulated proxies, and then the result can be compared to the known target.
The results of these experiments depend on the properties of these pseudoproxies; a
higher signal to noise ratio will result in a better score for the reconstruction, or a
more complicated noise structure will result in a lower score. In order to get an
accurate assessment of the relative strengths and weaknesses of the various methods it
is important that the properties of the pseudoproxies are as realistic as possible. But to
facilitate interpretation the proxy model should also be as simple as possible.
Many pseudoproxy models add random errors – often either independent normal or
AR(1) errors – to a gridbox temperature series. A pseudoproxy may record
temperature information via a number of climate variables, and so the total climate
signal in a proxy record may be significantly underestimated if we limit the
pseudoproxy’s climate signal to a single gridbox temperature.
In fact ‘temperature plus noise’ pseudoproxies, with realistic correlations between the
proxy and the local temperature, produce pseudo-reconstructions with unrealistically
low calibration and validation performance. This suggests that more climate
information needs to be included in pseudoproxy models.
Abstracts 96