NG33C-02
The climate continuum revisited 

Wednesday, 16 December 2015: 15:10
104 (Moscone South)
Julien Emile-Geay1, Jianghao Wang1 and Judson Wiley Partin2, (1)University of Southern California, Los Angeles, CA, United States, (2)University of Texas at Austin, Austin, TX, United States
Abstract:
A grand challenge of climate science is to quantify the extent of natural variability on adaptation-relevant timescales (10-100y). Since the instrumental record is too short to adequately estimate the spectra of climate measures, this information must be derived from paleoclimate proxies, which may harbor a many-to-one, non-linear (e.g. thresholded) and non-stationary relationship to climate. In this talk, I will touch upon the estimation of climate scaling behavior from climate proxies. Two case studies will be presented:

  1. an investigation of scaling behavior in a reconstruction of global surface temperature using state-of- the-art data [PAGES2K Consortium, in prep] and methods [Guillot et al., 2015]. Estimating the scaling exponent β in spectra derived from this reconstruction, we find that 0 < β < 1 in most regions, suggesting long-term memory. Overall, the reconstruction-based spectra are steeper than the ones based on an instrumental dataset [HadCRUT4.2, Morice et al., 2012], and those estimated from PMIP3/CMIP5 models, suggesting the climate system is more energetic at multidecadal to centennial timescales than can be inferred from the short instrumental record or from the models developed to reproduce it [Laepple and Huybers, 2014].

  2. an investigation of scaling behavior in speleothems records of tropical hydroclimate. We will make use of recent advances in proxy system modeling [Dee et al., 2015] and investigate how various aspects of the speleothem system (karst dynamics, age uncertainties) may conspire to bias the estimate of scaling behavior from speleothem timeseries. The results suggest that ignoring such complications leads to erroneous inferences about hydroclimate scaling.

References

Dee, S. G., J. Emile-Geay, M. N. Evans, Allam, A., D. M. Thompson, and E. J. Steig (2015), J. Adv. Mod. Earth Sys., 07, doi:10.1002/2015MS000447.

Guillot, D., B. Rajaratnam, and J. Emile-Geay (2015), Ann. Applied. Statist., pp. 324–352, doi:10.1214/14-AOAS794.

Laepple, T., and P. Huybers (2014), PNAS, doi: 10.1073/pnas.1412077111.

Morice, C. P., J. J. Kennedy, N. A. Rayner, and P. D. Jones (2012), JGR: Atmospheres, 117(D8), doi:10.1029/2011JD017187.

PAGES2K Consortium (in prep), A global multiproxy database for temperature reconstructions of the Common Era, Scientific Data.

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