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Indian Ocean warming could weaken Summer Monsoon rainfall in South Asia
The South Asian monsoon, also known as Indian Summer Monsoon (ISM), is crucial for the food security and socioeconomic well-being of 40% of the world’s population. From a historical perspective, fluctuations in monsoon rainfall have been linked to the rise and fall of civilizations in the Indian subcontinent. Now researchers are increasingly concerned that global warming may threaten the stability of the monsoon system, but accurate predictions have been hampered by the lack of long-term climate data in the Indian subcontinent.
A new study in the Proceedings of the National Academy of Sciences, by a team of researchers from the Max Planck Institute for the Science of Human History, Kiel University and the Alfred Wegener Institute of the Helmholtz Centre for Polar and Marine Research, seeks to strengthen climate predictions by reconstructing Indian Summer Monsoon rainfall changes during the past 130,000 years.
The study reports for the first time that the Indian Summer Monsoon, during the Last Interglacial, was weakened by sustained high sea surface temperatures in the equatorial and tropical Indian Ocean, indicating that modern rises in sea temperature could increase droughts in South Asia.
Solar radiation is often considered the primary influencer of the Indian Summer Monsoon’s intensity, with elevated solar radiation increasing humidity, wind circulation, and ultimately precipitation. Higher levels of solar radiation during the Last Interglacial should have, therefore, led to increased monsoon intensity, but this effect has never been verified with paleo-proxy data.
To reconstruct past Indian Summer Monsoon rainfall, the researchers analysed a 10-meter-long marine sediment core, retrieved from the northern Bay of Bengal, roughly 200 km south of the mouth of the Ganges-Brahmaputra-Meghna rivers. By analysing the stable hydrogen and carbon isotopes in leaf wax biomarkers, preserved in the sediment, researchers were able to track changes in rainfall during the planet’s last two warmer climate states: The Last Interglacial, which occurred 130,000-115,000 years ago, and the current warm period, the Holocene, which began 11,600 years ago.
Although solar insolation was higher during the Last Interglacial, isotopic analysis on leaf wax biomarker revealed that the Indian Summer Monsoon was actually less intense than in the Holocene. “This unexpected finding not only contrasts with paleoclimate model simulations,” says lead author Dr. Yiming Wang, paleo-climatologist at the Max Planck Institute for the Science of Human History, “but also challenges common assumptions that incoming solar insolation is the biggest factor in monsoon variability in a warm climate state.”
To identify the main driver of the monsoon’s rainfall during warm climate states, the researchers compared available reconstructions of past sea surface temperature from the Indian Ocean and found that the equatorial and tropical regions were 1.5-2.5°C warmer during the Last Interglacial period than during the Holocene. In addition, the researchers use paleoclimate model simulations to show that when the Indian Ocean’s surface temperature rose in the past, monsoon rainfall would decrease on land and increase in the sea above the Bay of Bengal.
“Our work strongly suggests that sea surface temperature plays a dominant role in shaping the Indian Summer Monsoon’s variability in South Asia,” says Dr. Wang, “and that higher surface temperatures in the Indian Ocean during the Last Interglacial period could have dampened the ISM intensity.”
The team’s results indicate that, due to increasing sea surface temperatures in the Indian Ocean, Indian Summer Monsoon failures are likely to increase as well. To what extent sea surface temperature affects monsoon intensity in other tropical regions remains an open question.
“The obvious discrepancy between our data and prevailing climate model simulations underscores the importance of hydroclimate proxy records for understanding the range and rate of climate change in the past,” says Prof. Ralph Schneider, senior author of the study, paleoclimate researcher at the Institute of Geosciences and the Leibniz Laboratory for Radiometric Dating and Stable Isotope Research at Kiel University. “Our results show that, in addition to the effect of solar radiation on continents, the effect of ocean warming on precipitation intensity needs to be re-evaluated in climate models.”
“Changes in the hydrological cycle will affect agricultural land, natural ecosystems, and consequently the livelihoods of billions of people,” Dr. Wang emphasises. “We therefore need to improve our understanding of the control mechanisms of summer monsoon rainfall to better predict weather extremes such as droughts and floods and devise adaptation measures. Time is of the essence, especially if ocean warming continues at the rate it is.”
News
Fuel crunch looms
Govt. tells fuel distributors to maintain stocks to ensure uninterrupted supplies
by Saman Indrajith and Norman Palihawadane
The government had instructed private fuel distributors to maintain minimum stocks and ensure uninterrupted supplies to the market, Energy Minister Anura Karunathilaka told Parliament yesterday (06).
Karunathilaka said the Ministry of Energy Secretary had notified the relevant companies of the requirement, following a reduction in supplies by some private distributors, amid higher international fuel prices.
The Minister said private companies had informed the government that they were facing losses because international prices had risen while fuel was being sold, locally, at prevailing prices. As a result, some companies had reduced the volumes released to the market.
The reduced supplies had increased the burden on the Ceylon Petroleum Corporation (CPC), whose share of the diesel market had risen from about 54% to 82%, the Minister said.
“The CPC currently holds an 82% share of the market,” he said, adding that it had increased its supplies, compared with February, to compensate for the reduction by private distributors.
Karunathilaka said the government could not, under the existing agreements with private companies, specify the quantities they should supply to individual filling stations. However, it could require them to maintain minimum stocks in the country.
The Minister said the Energy Ministry had already instructed companies that had failed to maintain the required stocks to take steps to prevent supply disruptions.
The Minister attributed the queues reported at some filling stations to reduced supplies from private distributors, as well as normal variations in fuel distribution. He also said demand for CPC fuel had increased because private companies generally did not provide fuel to dealers on credit, while the CPC offered a three-day credit facility.
“We expect that, as the Ceylon Petroleum Corporation takes on this additional burden, the problem will ease to some extent by Wednesday or Thursday,” Karunathilaka said.
He said instructions had also been issued to increase supplies to CPC filling stations. A special discussion on the issue is scheduled for today (07), with officials of the Energy Ministry and CPC expected to participate,
along with President Anura Kumara Dissanayake.
Meanwhile, Petroleum Dealers’ Association officials have called for an early solution to the supply issue. Association Chairman D.V. Shantha Silva said queues had been reported at many filling stations, mainly those operated by private distributors.
He said the situation was not due to an overall shortage of fuel, but was linked to reduced orders by Lanka IOC, Sinopec and R.M. Parks amid concerns over losses incurred on fuel sales.
The Ceylon Petroleum Private Tanker Owners Association has urged motorists to refrain from panic buying, saying there was no nationwide disruption to fuel supplies.
The government earlier increased fuel prices and introduced a per-litre diesel subsidy following concerns raised by distributors over rising international prices.
News
Gnansara Thera to be assigned to prison printing section: Officials
by Norman Palihawadane
Bodu Bala Sena General Secretary Ven. Galagodaatte Gnanasara Thera, who has been ordered by the court to serve the remainder of his prison sentence, is to be assigned to the prison ‘printing work party’, prison officials said yesterday.
The monk was produced before the Colombo High Court yesterday by prison officials in connection with a warrant issued by the court.
He appeared before the court in civilian attire.
Prison sources said arrangements were being finalised for his detention and that he would subsequently be assigned to the printing work party.
The Thera initially objected when prison officials instructed him to change from his robes into the attire worn by convicted prisoners.
He later agreed to wear the prescribed prison clothes, sources said.
The Supreme Court, in September, annulled the presidential pardon granted to Gnanasara Thera in 2019. He had been serving a six-year prison sentence imposed following his conviction for contempt of court but had served only about nine months when then President Maithripala Sirisena granted him a presidential pardon in May 2019.
Following the Supreme Court ruling, the Thera was required to serve the remainder of his sentence. He was subsequently reported missing, prompting the Court of Appeal to issue an open warrant for his arrest.
The Court of Appeal on Monday ordered the authorities to enforce the remainder of his prison sentence.
News
Speaker rejects Ajith Perera’s privilege complaint
Speaker Dr. Jagath Wickramaratne yesterday ruled that a privilege complaint submitted by SJB Kalutara District MP Ajith P. Perera did not constitute a prima facie breach of parliamentary privilege.
The ruling was made in response to a notice of privilege submitted by Perera on October 02.
Perera alleged that his parliamentary privileges had been breached over the failure to take formal action or reach a final decision on a written request submitted on August 03 by 18 Opposition MPs seeking the appointment of a Special Select Committee to investigate delays in the judicial system and prison overcrowding.
He had also requested that the matter be referred to the Committee on Ethics and Privileges for investigation and recommendations.
In his ruling, Speaker Wickramaratne said the Speaker, as the Presiding Authority and guardian of the powers, rights and privileges of Parliament, could not be subjected to a privilege complaint or disciplinary inquiry by a committee subordinate to the Chair in respect of actions taken in an official capacity.
He said that, under the Standing Orders, the Speaker was required to independently determine whether a prima facie case of breach of privilege existed.
Referring a complaint against the Speaker to a committee functioning under the Speaker’s authority would, therefore, create a procedural contradiction, he said.
Accordingly, the Speaker ruled that Perera’s notice did not constitute a prima facie breach of parliamentary privilege and disallowed the request to refer the matter to the Committee on Ethics and Privileges.
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