 |
| Titel |
Experimental Reconstructions of Surface Temperature using the PAGES 2k Network |
| VerfasserIn |
Jianghao Wang, Julien Emile-Geay, Adam Vaccaro, Dominique Guillot, Bala Rajaratnam |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094053
|
| Publikation (Nr.) |
 EGU/EGU2014-9375.pdf |
|
|
|
|
|
| Zusammenfassung |
| Climate field reconstructions (CFRs) of the Common Era provide uniquely detailed
characterizations of natural, low-frequency climate variability beyond the instrumental era.
However, the accuracy and robustness of global-scale CFRs remains an open question. For
instance, Wang et al. (2013) showed that CFRs are greatly method-dependent, highlighting
the danger of forming dynamical interpretations based on a single reconstruction (e.g. Mann
et al., 2009).
This study will present a set of new reconstructions of global surface temperature and
compare them with existing reconstructions from the IPCC AR5. The reconstructions are
derived using the PAGES 2k network, which is composed of 501 high-resolution
temperature-sensitive proxies from eight continental-scale regions (PAGES2K Consortium,
2013). Four CFR techniques are used to produce reconstructions, including RegEM-TTLS,
the Mann et al. (2009) implementation of RegEM-TTLS (hereinafter M09-TTLS), CCA
(Smerdon et al., 2010) and GraphEM (Guillot et al., submitted).
First, we show that CFRs derived from the PAGES 2k network exhibit greater
inter-method similarities than the same methods applied to the proxy network of Mann et al.
(2009) (hereinafter M09 network). For instance, reconstructed NH mean temperature series
using the PAGES 2k network are in better agreement over the last millennium than the
M09-based reconstructions. Remarkably, for the reconstructed temperature difference
between the Medieval Climate Anomaly and the Little Ice Age, the spatial patterns
of the M09-based reconstructions are greatly divergent amongst methods. On the
other hand, not a single PAGES 2k-based CFR displays the La Niña-like pattern
found in Mann et al. (2009); rather, no systematic pattern emerges between the two
epochs.
Next, we quantify uncertainties associated with the PAGES 2k-based CFRs via ensemble
methods, and show that GraphEM and CCA are less sensitive to random noise than
RegEM-TTLS and M09-TTLS, consistent with pseudoproxy studies (Wang et al.,
2014). The updated set of reconstructions, with uncertainties, will provide a broader
context for the evaluation of the unusual character of the 20th century warming.
The reconstructions will also be used to constrain fingerprinting analyses, which is
particularly useful in discriminating between externally forced signals and internal
variability.
Reference:
Guillot, D., B. Rajaratnam, and J. Emile-Geay, Statistical paleoclimate reconstructions
via markov random fields, Ann. Appl. Stat., submitted.
Mann, M. E., Z. Zhang, S. Rutherford, R. S. Bradley, M. K. Hughes, D. Shindell,
C. Ammann, G. Faluvegi, and F. Ni, Global signatures and dynamical origins of
the little ice age and medieval climate anomaly, Science, 326 (5957), 1256–1260,
2009.
PAGES2K Consortium, Continental-scale temperature variability during the past two
millennia, Nature Geosci, 6(5), 339–346, 2013.
Smerdon, J. E., A. Kaplan, D. Chang, and M. N. Evans, A pseudoproxy evaluation of the
CCA and RegEM methods for reconstructing climate fields of the last millennium*, J. Clim.,
23(18), 4856–4880, 2010.
Wang, J., J. Emile-Geay, A. D. Vaccaro, and D. Guillot, Fragility of estimated spatial
temperature patterns in climate field reconstructions of the Common Era, Abstract PP41B-03
presented at Fall Meeting, AGU, San Francisco, Calif., 2013.
Wang, J., J. Emile-Geay, D. Guillot, J. Smerdon, and B. Rajaratnam, Evaluating climate
field reconstruction techniques using improved emulations of real-world conditions,
Clim.Past, 10(1), 1–19, 2014. |
|
|
|
|
|
|