A few prospective ideas on climate reconstruction: from a statistical single proxy approach towards a multi-proxy and dynamical approach

Abstract

Abstract. Important progresses have been made in palaeoclimatological studies by using statistical methods. But they are in somewhere limited as they take the present as an absolute reference. This is particularly true for the modern analogue technique. The availability of mechanistic models to simulate the proxies measured in the sediment cores gives now the possibility to relax this constraint. In particular, vegetation models provide outputs comparable to pollen data (assuming that there is a relationship between plant productivity and pollen counts). The input of such models is, among others, climate. The idea behind paleoclimatological reconstructions is then to obtain inputs, given outputs. This procedure, called model inversion, can be achieved with appropriate algorithms in the frame of the Bayesian statistical theory. But we have chosen to present it in an intuitive way, avoiding the mathematics behind it. Starting from a relative simple application, based on an equilibrium BIOME3 model with a single proxy (pollen), the approach has evolved into two directions: (1) by using several proxies measured on the same core (e.g. lake-level status and δ 13 C) when they are related to a component of the vegetation, and (2) by using a more complex vegetation model, the dynamic vegetation model LPJ-GUESS. Examples presented (most of them being already published) concern Last Glacial Maximum in Europe and Africa, Holocene in a site of the Swiss Jura, anCorrespondence to: J. Guiot (guiot@cerege.fr) Eemian site in France. The main results are that: (1) pollen alone is not able to provide exhaustive information on precipitation, (2) assuming past CO 2 equivalent to modern one may induce biases in climate reconstruction, (3) vegetation models seem to be too much constrained by temperature relative to precipitation in temperate regions. This paper attempts to organise some recent ideas in the palaeoclimatological reconstruction domain and to propose prospectives in that effervescent domain.

Strengths and Weaknesses of Quantitative Climate Reconstructions Based on Late-Quaternary Biological Proxies

“…Such approaches based on forward modelling have been increasingly used in recent years using Bayesian statistics (e.g. Guiot et al 1999Guiot et al , 2009Haslett et al 2006;Hatté et al 2009;Haslett & Challenor 2010) and it is expected that their importance and relevance will continue to increase with increasing computational resources and our understanding about the relationships between climate parameters and proxy responses.…”

“…assemblage composition) of the proxy-indicator (e.g. Guiot et al 2000Guiot et al , 2009. For example, Guiot et al (2000) used a mechanistic model of vegetation expressed as a function of climate.…”

“…In this approach, several most likely climate scenarios are estimated for the time period in question, the vegetation model is run with each scenario and the simulated vegetation types are compared with the fossil pollen data to estimate the most coherent simulations. The past climate is obtained by inverting the climate input from the vegetation model (Guiot et al 1999(Guiot et al , 2009Garreta et al 2010). Wu et al (2007a) used an inverse modelling approach with modern and glacial CO 2 concentrations to investigate the impact of changing CO 2 concentration on the reconstruction results from Africa and Eurasia.…”

Pollen-based continental climate reconstructions at 6 and 21 ka: a global synthesis

“…Hatté et al (2009) showed that the use of d 13 C as an additional constraint considerably reduces the uncertainties of climatic reconstructions obtained from inverse modelling compared to using pollen alone. Guiot et al (2009) have indicated that inverse modelling could provide an elegant solution of combining multiple data types, including lake-levels, d…”

Towards the assimilation of tree-ring-width records using ensemble Kalman filtering techniques

“…"High resolution" proxy records (Hughes and Ammann 2009) offer information about inter-annual and slower internal climate variabilities which in principle could be constrained by a suitable DA scheme. As a result, several research groups have been actively working with the purpose of paving the way towards an eventual paleo-reanalysis (Hughes et al 2010;Guiot et al 2009;Brönnimann 2011).…”