Wednesday, February 19, 2014

New paper finds another amplification mechanism by which the Sun controls drought & climate

A new paper published in Earth and Planetary Science Letters reconstructs droughts in India over the past 6,000 years and finds droughts were much more severe and prolonged in the past. Two prolonged droughts are identified, between 4,600 to 3,900 years ago [lasting 700 years] and between 2,000 to 600 years ago [lasting 1,400 years!]. Modern droughts are shown to be not unusual or unprecedented in comparison. 

The paper also shows a decrease of intensity and frequency of El Nino events over the past 2000-3000 years, opposite of the claims of climate alarmists predicting an increase of intensity and frequency. 

The authors find a linkage between solar activity and droughts and the Indian Summer Monsoon. The paper adds to many other peer-reviewed published papers finding solar activity controls the hydrological cycle and climate via solar amplification mechanisms by which tiny 0.1% changes of total solar irradiance can be amplified to produce large effects on climate, including modulation of natural atmospheric and ocean oscillations such as the Southern OscillationNorth Atlantic Oscillation, Scandinavian Pattern, Quasi Biennial Oscillation (QBO), Indian Summer Monsoon, El Nino Southern Oscillation [ENSO], Pacific Decadal Oscillation, Pacific-North American Oscillation, East Asian Monsoon, Madden-Julian Oscillation, and others. Other amplification mechanisms include via ozone and sunshine hours/clouds.

Horizontal axis is thousands of years before the present. Second graph shows a decrease in El Nino intensity since the Minoan Warm Period 3,000 years ago. Bottom graphs show modern droughts are not unusual or unprecedented. 
First high resolution Holocene reconstruction from central India.
Two extended late Holocene droughts identified.
Indian monsoon and ENSO link established only ca. 2 cal ka BP.
Localised warming in Indo Pacific forces Indian droughts.
Cultural settlements linked to droughts.


Concerns about the regional impact of global climate change in a warming scenario have highlighted the gaps in our understanding of the Indian Summer Monsoon (ISM, also referred to as the Indian Ocean summer monsoon) and the absence of long term palaeoclimate data from the central Indian core monsoon zone (CMZ). Here we present the first high resolution, well-dated, multiproxy reconstruction of Holocene palaeoclimate from a 10 m long sediment core raised from the Lonar Lake in central India. We show that while the early Holocene onset of intensified monsoon in the CMZ is similar to that reported from other ISM records, the Lonar data shows two prolonged droughts (PD, multidecadal to centennial periods of weaker monsoon) between 4.6–3.9 and 2–0.6 cal ka. A comparison of our record with available data from other ISM influenced sites shows that the impact of these PD was observed in varying degrees throughout the ISM realm and coincides with intervals of higher solar irradiance. We demonstrate that (i) the regional warming in the Indo-Pacific Warm Pool (IPWP) plays an important role in causing ISM PD through changes in meridional overturning circulation and position of the anomalous Walker cell; (ii) the long term influence of conditions like El Niño-Southern Oscillation (ENSO) on the ISM began only ca. 2 cal ka BP and is coincident with the warming of the southern IPWP; (iii) the first settlements in central India coincided with the onset of the first PD and agricultural populations flourished between the two PD, highlighting the significance of natural climate variability and PD as major environmental factors affecting human settlements.

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