Inter-hemispheric linkages in climate change: paleo-perspectives for future climate change

Abstract

Abstract. The Pole-Equator-Pole (PEP) projects of the PANASH (Paleoclimates of the Northern and Southern Hemisphere) programme have significantly advanced our understanding of past climate change on a global basis and helped to integrate paleo-science across regions and research disciplines. PANASH science allows us to constrain predictions for future climate change and to contribute to the management of consequent environmental changes. We identify three broad areas where PEP science makes key contributions.1. The pattern of global changes. Knowing the exact timing of glacial advances (synchronous or otherwise) during the last glaciation is critical to understanding interhemispheric links in climate. Work in PEPI demonstrated that the tropical Andes in South America were deglaciated earlier than the Northern Hemisphere (NH) and that an extended warming began there ca. 21 000 cal years BP. The general pattern is consistent with Antarctica and has now been replicated from studies in Southern Hemisphere (SH) regions of the PEPII transect. That significant deglaciation of SH alpine systems and Antarctica led deglaciation of NH ice sheets may reflect either i) faster response times in alpine systems and Antarctica, ii) regional moisture patterns that influenced glacier mass balance, or iii) a SH temperature forcing that led changes in the NH. This highlights the limitations of current understanding and the need for further fundamental paleoclimate research.2. Changes in modes of operation of oscillatory climate systems. Work across all the PEP transects has led to the recognition that the El Niño Southern Oscillation (ENSO) phenomenon has changed markedly through time. It now appears that ENSO operated during the last glacial termination Correspondence to: J. Shulmeister (james.shulmeister@canterbury.ac.nz) and during the early Holocene, but that precipitation teleconnections even within the Pacific Basin were turned down, or off. In the modern ENSO phenomenon both inter-annual and seven year periodicities are present, with the inter-annual signal dominant. Paleo-data demonstrate that the relative importance of the two periodicities changes through time, with longer periodicities dominant in the early Holocene.3. The recognition of climate modulation of oscillatory systems by climate events. We examine the relationship of ENSO to a SH climate event, the Antarctic cold reversal (ACR), in the New Zealand region. We demonstrate that the onset of the ACR was associated with the apparent switching on of an ENSO signal in New Zealand. We infer that this related to enhanced zonal SW winds with the amplification of the pressure fields allowing an existing but weak ENSO signal to manifest itself. Teleconnections of this nature would be difficult to predict for future abrupt change as boundary conditions cannot readily be specified. Paleo-data are critical to predicting the teleconnections of future changes.

Polar Climate Instability and Climate Teleconnections from the Arctic to the Midlatitudes and Tropics

“…With the Moy et al (2002) record stressing millennial-scale ENSO variability and the Rein et al (2005) record emphasizing multidecadal variability, we are left with the impression that ENSO may well have evolved on many different time scales. For a concise review of reconstructed paleo-ENSO behavior during the last deglaciation the reader is referred to Shulmeister et al (2006), who suggest that multiple modes contributing to ENSO periodicity may have been active throughout deglaciation.…”

Re‐analysis of key evidence in the case for a hemispherically synchronous response to the Younger Dryas climatic event

“…One of the most significant, yet controversial, issues in palaeoclimate research surrounds the mechanism by which climate signals are transferred from the area of forcing to the rest of the globe and the timescales of such responses (Shulmeister et al, 2006). Improved understanding of the cause, timing and spatial extent of millennial-scale climate events is essential for accurately identifying teleconnections, building accurate palaeoclimate models and producing robust climate projections.…”

The southern Brazilian tropical forest during the penultimate Pleistocene glaciation and its termination

“…The American continent is continuous nearly from pole to pole and thus provides an excellent laboratory for examination of the connections between high and low latitudes in both hemispheres, more specifically the climatic teleconnections in the Southern Hemisphere (Markgraf, 2001; Shulmeister et al, 2006). Since the mid‐Pleistocene, the expansion and regression phases of ice volume have been orbitally paced by a 100 000‐year cycle that, in turn, has affected the tropical hydrological cycle in the high Andes (Hanselman et al, 2011; Torres et al, 2013; Rodbell et al, 2022) as well as in the lowlands (Kern et al, 2023).…”