 |
| Titel |
Evidence of inter-hemispheric temperature contrasts over the last millennium from a new Southern Hemisphere multi-proxy reconstruction |
| VerfasserIn |
Raphael Neukom, Joelle Gergis, David Karoly, Heinz Wanner, Mark Curran, Julie Elbert, Fidel González-Rouco, Braddock Linsley, Andrew Moy, Ignacio Mundo, Christoph Raible, Eric Steig, Tas van Ommen, Tessa Vance, Ricardo Villalba, Jens Zinke, David Frank |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092371
|
| Publikation (Nr.) |
 EGU/EGU2014-6708.pdf |
|
|
|
|
|
| Zusammenfassung |
| The instrumental temperature record shows distinct inter-hemispheric temperature
differences superimposed on the common warming trend over the last 150 years.
Asynchronicity between the hemispheres is also suggested by millennial-scale analyses
over the last deglaciation and the Holocene, indicating a significant modulation of
the response to external forcing by internal climate system variability on multiple
temporal scales. However, on multi-decadal to centennial times-scales, quantitative
analyses on inter-hemispheric temperature variability are largely missing due to
the lack of hemispheric-scale high-resolution reconstructions from the Southern
Hemisphere.
We introduce a new annually resolved multi-proxy ensemble reconstruction of Southern
Hemisphere mean temperatures over the last 1000 years. The reconstruction is based on an
unprecedented network of 325 proxy records yielding 111 temperature sensitive
predictors.
In 99.7% of the reconstruction ensemble members, the warmest decade of the last millennium
occurs after 1970. Comparing our results with an ensemble of Northern Hemisphere mean
reconstructions, we identify periods, where both hemispheres simultaneously exhibit extreme
temperatures (defined as exceeding ±1 standard deviations of 1000-2000 temperatures). The
only pre-industrial period where >33% of ensemble members indicate globally synchronous
extremes is the cold phase between 1594 and 1677. Simultaneous warm temperatures are
only identified in the years after 1974 (1979) where more than 66% (90%) of ensemble
members indicate extreme warmth. This suggests existence of a globally coherent peak
“Little Ice Age”, but no consistent “Medieval Climate Anomaly” during last 1000
years.
We then compare our ensemble of temperature reconstructions to an ensemble of 24 climate
model simulations. While the simulated globally consistent cold periods coincide with major
volcanic eruptions, the simulations do not account for key features of reconstructed
temperature variations over the last millennium.
Calculation of the reconstructed inter-hemispheric temperature difference (Northern
Hemisphere minus Southern Hemisphere; NS) shows that large fluctuations, such as the
Northern Hemisphere temperature drop around 1970, occurred repeatedly over the last
millennium. In contrast, the model simulations show much smaller inter-hemispheric
temperature differences: during 42% of the years within the past millennium, median
reconstructed NS differences are outside the 10th-90th percentile range of the climate model
simulations.
The over-estimated coherence between the hemispheres in the simulations suggests a strong
role of internal climate system variability relative to external forcing. This holds
particularly true for the Southern Hemisphere, which shows reduced correlations
between reconstructed and simulated temperatures (r=0.35) compared to the NH
(r=0.77). Our results imply that climate sensitivity and detection and attribution
studies, which are based on data from the Northern Hemisphere alone, may not be
representative for the global climate. We conclude that multi-decadal predictability of the
climate system on regional to global scales may be more limited than previously
estimated. |
|
|
|
|
|
|