New paper finds El Ninos were much more extreme in the past

A new paper published in Quaternary Science Reviews reconstructs the climate of tropical Western Australia over the past 9,000 years and finds the intensity of the Indonesian–Australian summer monsoon (IASM), which is driven by ENSO/El Nino activity, has declined over the past 5,000 years since the Holocene Climate Optimum. The paper adds to many other peer-reviewed publications demonstrating that, contrary to claims of climate alarmists, present-day climate is less variable and less extreme than during most of the Holocene [the past ~11,000 years].

Vertical axis shows d18O, a proxy of temperature and precipitation.
Horizontal axis is thousands of years before the present.

Frequency of El Ninos per 100 years shown in red in top graph. Charcoal abundance, a proxy of fire activity, is shown in orange in second graph and also indicates a decline over the past 4,000 years. Horizontal axis is thousands of years before the present.

A Stalagmite record of Holocene Indonesian–Australian summer monsoon variability from the Australian tropics

• Rhawn F. Denniston^a, , , 
• Karl-Heinz Wyrwoll^b, 
• Victor J. Polyak^c, 
• Josephine R. Brown^d, 
• Yemane Asmerom^c, 
• Alan D. Wanamaker Jr.^e, 
• Zachary LaPointe^c, 
• Rebecca Ellerbroek^a, 
• Michael Barthelmes^a,
• Daniel Cleary^a, 
• John Cugley^f, 
• David Woods^g, 
• William F. Humphreys^b, h, i

• ^a Department of Geology, Cornell College, Mount Vernon, IA, USA
• ^b University of Western Australia, Perth, Western Australia, Australia
• ^c Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM, USA
• ^d Centre for Australian Weather and Climate Research, Melbourne, Australia
• ^e Department of Geological and Atmospheric Sciences, Iowa State University, Ames, IA, USA
• ^f Kimberley Toad Busters, Kununurra, Western Australia, Australia
• ^g Department of Environment and Conservation, Broome, Western Australia, Australia
• ^h Western Australian Museum, Welshpool DC, Western Australia, Australia
• ⁱ University of Adelaide, Adelaide, South Australia, Australia

Highlights

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Holocene IASM reconstructed for tropical Western Australia.

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Phasing of monsoon strength similar to Borneo but opposite to Flores.

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ENSO, not ITCZ, best explains monsoon variability.

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Weak Late Holocene monsoon tied to peak El Niño activity.

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Abstract

Oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave KNI-51, located in the eastern Kimberley region of tropical Western Australia, represent the first absolute-dated, high-resolution speleothem record of the Holocene Indonesian–Australian summer monsoon (IASM) from the Australian tropics. Stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic Holocene IASM which strengthened in the early Holocene, decreased in strength by 4 ka, with a further decrease from ∼2 to 1 ka, before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka. The relationships between the KNI-51 IASM reconstruction and those from published speleothem time series from Flores and Borneo, in combination with other data sets, appear largely inconsistent with changes in the position and/or organization of the Intertropical Convergence Zone (ITCZ). Instead, we argue that the El Niño/Southern Oscillation (ENSO) may have played a dominant role in driving IASM variability since at least the middle Holocene. Given the muted modern monsoon rainfall responses to most El Niño events in the Kimberley, an impact of ENSO on regional monsoon precipitation over northwestern Australia would suggest non-stationarity in the long-term relationship between ENSO forcing and IASM rainfall, possibly due to changes in the mean state of the tropical Pacific over the Holocene.