Identification of climatic state with limited proxy data RIGC/JAMSTEC, 3173-25 Showamachi, Yokohama, Japan
10 Jul 2012
Received: 20 January 2012 – Published in Clim. Past Discuss.: 31 January 2012 Abstract. We investigate the identifiability of the climate by limited proxy data. We
test a data assimilation approach through perfect model pseudoproxy
experiments, using a simple likelihood-based weighting based on the particle
filtering process. Our experimental set-up enables us to create a massive
10 000-member ensemble at modest computational cost, thus enabling us to
generate statistically robust results. We find that the method works well
when data are sparse and imprecise, but in this case the reconstruction has a
rather low accuracy as indicated by residual RMS errors. Conversely, when
data are relatively plentiful and accurate, the estimate tracks the target
closely, at least when considering the hemispheric mean. However, in this
case, our prior ensemble size of 10 000 appears to be inadequate to
correctly represent the true posterior, and the regional performance is poor.
Using correlations to assess performance gives a more encouraging picture,
with significant correlations ranging from about 0.3 when data are sparse to
values over 0.7 when data are plentiful, but the residual RMS errors are
substantial in all cases. Our results imply that caution is required in
interpreting climate reconstructions, especially when considering the
regional scale, as skill on this basis is markedly lower than on the large
scale of hemispheric mean temperature.
Revised: 29 May 2012 – Accepted: 15 June 2012 – Published: 10 July 2012
Citation: Annan, J. D. and Hargreaves, J. C.: Identification of climatic state with limited proxy data, Clim. Past, 8, 1141-1151, doi:10.5194/cp-8-1141-2012, 2012.