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Indian Ocean warming could weaken Summer Monsoon rainfall in South Asia

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File photo of residents walk along a flooded road in Piliyandala in 2010 following monsoon rains

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.”



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BASL urges President to de-escalate tensions in different parts of country

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The Bar Association of Sri Lanka has called upon President Gotabaya Rajapaksa to instruct the Defence Secretary, the Commanders of the Tri Forces and the Inspector General of Police to ensure that there is an immediate de-escalation of tensions in different parts of the country – especially at fuel stations – understanding the difficulties faced by the public.”

 “Whilst keeping in mind that the police and armed forces are acting under very trying circumstances, nevertheless it is necessary to give strict instructions to the police and the forces to desist from violence in dealing with the public and to act with utmost restraint”, the BASL has said in a media statement.

 “We also call upon you to ensure that steps are taken under the law to deal with errant officers who have subjected civilians to such violence.”

The BASL is of the view that it is not appropriate for service personnel to be deployed in the present manner in matters which essentially should be managed by the Sri Lanka Police.

 The armed forces should also not be used to disturb or hinder peaceful protests as was seen last week in Galle.

Full text of the BASL letter to the President:

The Bar Association of Sri Lanka (BASL) expresses its gravest concerns at the current situation at fuel stations throughout the country and the reports of several incidents of conflicts between civilians and members of the police force and the armed forces at fuel stations. There has been video footage of civilians being assaulted by personnel of the armed forces and the police, the latest being of a civilian being kicked by an Army officer at a fuel station. There have also been situations of the police and Army opening fire into the air to contain the crowd.

Your Excellency is no doubt aware that thousands of desperate civilians are waiting in queues at hundreds of fuel stations in the country. The queues are kilometres long. The tension at the fuel stations have arisen from this desperation for which there is no immediate solution in sight.

The BASL wishes to warn Your Excellency of the imminent dangers this situation could give rise to. The present unrest could result in a conflagration between civilians and members of the armed forces or the police. Some years ago, confrontations between members of the public and the armed forces resulted in the deaths of civilians. Such incidents between the members of the armed forces or the police and the civilians will discredit Sri Lanka’s armed forces and the police.

We call upon Your Excellency to take all necessary steps to give instructions to the Defence Secretary, the Commanders of the Tri Forces and the Inspector General of Police to ensure that there is an immediate de-escalation of the situation in different parts of the country – especially at fuel stations – understanding the difficulties faced by public. Whilst keeping in mind that the police and armed forces are acting under very trying circumstances, nevertheless it is necessary to give strict instructions to the police and the forces to desist from violence in dealing with the public and to act with utmost restraint. We also call upon you to ensure that steps be taken under the law to deal with errant officers who have subjected civilians to such violence.

The Sri Lanka Army and other service personnel must be deployed only in very limited circumstances as contemplated in the Criminal Procedure Code. The BASL is of the view that it is not appropriate for service personnel to be deployed in the present manner in matters which essentially should be managed by the Sri Lanka Police. The Armed Forces should also not be used to disturb or hinder peaceful protests as was seen last week in Galle.

We trust that this will receive the immediate attention of the Government as to do otherwise may otherwise result in unprecedented turmoil and harm.

The BASL believes that the ultimate solution to the situation at fuel stations is to be transparent with the public and to ensure an equitable and effective system of fuel distribution throughout the country.

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SC orders AG to submit report on fuel purchases and distribution

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By A.J.A. Abeynayake

A three-member Supreme Court bench consisting of Justices Vijith Malalgoda, Mahinda Samayawardena and Arjuna Obeysekera yesterday ordered the Attorney General to submit a report on fuel purchases, the distribution thereof and the sectors to be provided with fuel on a priority basis.

The Supreme Court made the order after considering two fundamental rights petitions presented by the Bar Association of Sri Lanka.

The BASL has requested the Supreme Court to direct the Cabinet of Ministers to consult all stakeholders and independent experts to formulate and implement the necessary policies, and to provide concessions in relation to the prices of essential goods and services to the people including LP gas, fuel, electricity, milk powder, medicines and food.

The petitions were filed by the President of the BASL Saliya Pieris PC, Deputy President Anura Meddegoda PC, former Secretary Rajeev Amarasuriya, Treasurer Rajindh Perera and the Assistant Secretary Pasindu Silva.

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A/L may be delayed by one month

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Education Minister Sushil Premajayantha told Parliament yesterday that although it had been scheduled to hold the G.C.E. A/L Examination 2022 in November this year, it could be further delayed by another month.

Responding to a question by MP Shantha Bandara, the Minister said: “The examination should be held at least after three months of releasing the results of the previous A/L exam because the students who need to sit it again should have enough time to prepare,” the Minister said.

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