Was the Little Ice Age more or less El Niño-like than the Medieval Climate Anomaly? Evidence from hydrological and temperature proxy data

Abstract

Abstract. The El Niño-Southern Oscillation (ENSO) is the most important source of global climate variability on interannual timescales and has substantial environmental and socio-economic consequences. However, it is unclear how it interacts with large-scale climate states over longer (decadal to centennial) timescales. The instrumental ENSO record is too short for analysing long-term trends and variability and climate models are unable to accurately simulate past ENSO states. Proxy data are used to extend the record, but different proxy sources have produced dissimilar reconstructions of long-term ENSO-like climate change, with some evidence for a temperature-precipitation divergence in ENSO-like climate over the past millennium, in particular during the Medieval Climate Anomaly (MCA; AD ∼ 800-1300) and the Little Ice Age (LIA; AD ∼ 1400-1850). This throws into question the stability of the modern ENSO system and its links to the global climate, which has implications for future projections. Here we use a new statistical approach using weighting based on empirical orthogonal function (EOF) to create two new large-scale reconstructions of ENSOlike climate change derived independently from precipitation proxies and temperature proxies. The method is developed and validated using model-derived pseudo-proxy experiments that address the effects of proxy dating error, resolution, and noise to improve uncertainty estimations. We find no evidence that temperature and precipitation disagree over the ENSO-like state over the past millennium, but neither do they agree strongly. There is no statistically significant difference between the MCA and the LIA in either reconstruction. However, the temperature reconstruction suffers from a lack of high-quality proxy records located in ENSO-sensitive regions, which limits its ability to capture the large-scale ENSO signal. Further expansion of the palaeo-database and improvements to instrumental, satellite, and model representations of ENSO are needed to fully resolve the discrepancies found among proxy records and establish the long-term stability of this important mode of climatic variability.

Teleconnections and relationship between the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) in reconstructions and models over the past millennium

“…5 comprises those of equal sign. Temperature patterns during positive ENSO-SAM correlations and when both indices are of opposite sign resemble the spatial patterns of a negative IPO (Henley, 2017; Fig. 4 top left).…”

“…Hence, little is still known about the tropical to extratropical teleconnections es-tablished by ENSO and SAM over this time period. Also, it is not known if the interplay between these indices exhibits long-term fluctuations and if these are driven by external forcing or internal variability, for instance via multidecadal modes of variability such as the Interdecadal Pacific Oscillation (IPO; Folland et al, 1999;Power et al, 1999;Henley, 2017).…”

Response to David Nash

“…Bird et al, 2011;Vuille et al, 2012;Apaéstegui et al, 2014). In addition, the possibility of dominant El Niño conditions during the LIA (Cobb et al, 2003;Langton et al, 2008) may also have played a role, although the question of how ENSO varied through the LIA is still debated (Yan et al, 2011;Henke et al, 2017;Emile-Geay et al, 2013).…”

“…The region is considered one of the most sensitive tropical regions to climate change, particularly through hydrological cycle impacts (Magrin et al, 2014;Giorgi, 2006). Rainfall anomalies are expected to impact streamflow, freshwater supplies, agriculture and food production (Hidalgo et al, 2013;Magrin et al, 2014). Additionally, extreme weather events lead to natural hazards, such as floods, landslides and droughts, with a cascade of social consequences (Magrin et al, 2014).…”

300 years of hydrological records and societal responses to droughts and floods on the Pacific coast of Central America

“…Bird et al, 2011;Vuille et al, 2012;Apaéstegui et al, 2014). In addition, the possibility of dominant El Niño conditions during the LIA (Cobb et al, 2003;Langton et al, 2008) may also have played a role, although the question of how ENSO varied through the LIA is still debated (Yan et al, 2011;Henke et al, 2017;Emile-Geay et al, 2013).…”