Evidence of wet-dry cycles and mega-droughts in the Eemian climate of southeast Australia

Hamish Mcgowan,Micheline Campbell,Andrew Lowry,John Nikolaus Callow,Henri Wong

doi:10.1038/s41598-020-75071-z

Abstract

Understanding past climate variability is critical to informing debate of likely impacts of global warming on weather and climate, and water resources. Here we present a near annual resolution reconstruction of climate developed from a speleothem that spans the Eemian [Marine Isotope Stage 5e (MIS 5e)] from 117,500 to 123,500 years BP—the most recent period in the Earth’s history when temperatures were similar to those of today. Using 25 Mg, 88Sr, and 137Ba as proxies, we show the first indication of solar and teleconnection cyclic forcing of Eemian climate in southeast Australia, a region at present often affected by severe drought and bushfires. We find evidence for multi-centennial dry periods interpreted as mega-droughts, and highlight the importance of understanding the causes of these in the context of a rapidly warming world, where temperatures are now, or projected to exceed those of the Eemian.

Highlights

Understanding past climate variability is critical to informing debate of likely impacts of global warming on weather and climate, and water resources
The climate of Australia is globally relevant, as it responds to key global teleconnection forcing, including El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and the Indian Ocean Dipole (IOD)
The Mg time series for GC001 (Fig. 2a) shows clear cycles of higher/lower concentrations with a marked increase occurring around 120,800 years Before Present (BP)

Summary

Introduction

Understanding past climate variability is critical to informing debate of likely impacts of global warming on weather and climate, and water resources. 129,000–116,000 years Before Present (BP)] is the most recent geologic period when global temperatures were similar to present, but in response to orbital forcing rather than greenhouse gas loading of the atmosphere While this makes the Eemian an imperfect analogue for near-future climate due to anthropogenic global warming, the latitudinal temperature distribution was similar to the p resent[1,2,3,4]. The climate of Australia is globally relevant, as it responds to key global teleconnection forcing, including El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and the Indian Ocean Dipole (IOD) It is relevant as the severity of recent droughts and bushfires have been linked to increasing temperatures caused by anthropogenic greenhouse gas e missions[10,11,12,13], thereby stimulating interest in understanding past warm climate conditions such as during MIS 5e. These were likely caused by irregular southward penetration of the Intertropical Convergence Zone (ITCZ) and decaying tropical cyclone(s) over the headwaters of the Lake Eyre Basin—conditions similar to those of today that deliver inflows to Lake Eyre

Methods

Results

Conclusion