Rapid Arctic sea ice decline to increase rain events across South Asia: Study

The paper suggested that intense rain events, like those recorded during the 2018 floods in Kerala or the 2013 floods in Uttarakhand, will increase in frequency

New Delhi: A rapid and significant decline in Arctic sea ice will lead to an increase in intense precipitation events (IPEs) across South Asia, exposing people to disasters associated with extreme rain, a recent research paper published in IOP Science said.

The Arctic sea-ice decline has been accelerating with climate change, the research paper published on May 6 said. (AP/ Representational image)

Climate scientists from the Indian Institute of Tropical Meteorology, the ministry of earth sciences, and others investigated the tropical rainfall response to the declining Arctic sea ice using observations and climate model simulations.

The Arctic sea ice decline has been accelerating with climate change, the research paper published on May 6 said.

The paper suggested that intense rain events, like those recorded during the 2018 floods in Kerala or the 2013 floods in Uttarakhand, will increase in frequency. Both of these events were intense precipitation events. Rainfall events that exceed a threshold of 150 mm day−1 (in a grid point) are counted as extreme rainfall events.

Scientists found an increase in IPEs, especially during the last two decades. Periods with higher IPEs are associated with a decline in June-July-August Arctic sea ice. The larger increase in IPEs in recent decades often co-occurs with larger Arctic sea ice loss, the paper said.

“Observational evidence and idealised model experiments, in which the Arctic becomes seasonally ice free under greenhouse warming, reveal association between the Arctic sea-ice decline and intense precipitation events (IPEs) over South Asia,” the paper said.

The enhanced Arctic sea ice melt increases mid-latitude waviness and intensifies the circumglobal teleconnection (CGT)-like pattern, while also strengthening the subtropical high over East Asia. This, together with a La Niña-like response in the Pacific, enhances mean summer monsoon rainfall over South Asia.

“The enhanced energy in the tropics and the anomalous mid-latitude intrusions due to the Arctic sea-ice melt provide a conducive environment for moisture convergence and intense summer monsoon precipitation events over South Asia. Our findings reveal that, in a future warming scenario, Arctic sea-ice melt is likely a contributing factor for the amplified mean and IPEs over the South Asian region,” it said.

The June–July–August sea ice concentration in the Arctic is projected to decline under future warming scenarios. The intergovernmental panel on Climate Change’s Sixth Assessment Report estimates that Arctic September sea ice may vanish by the mid-21st century.

A sharp decline in the Arctic sea ice anomaly is evident in most emission scenarios, particularly from the mid-century onward. “Given the observed link between Arctic sea-ice decline and South Asian IPEs, the potential impacts of projected sea-ice loss on IPEs were analysed...we assessed changes in IPE intensity for various global warming levels, calculated relative to the 1850–1900 baseline,” the paper said.

“In summary, Arctic sea ice decline weakens the upper atmospheric circulation and alters energetics, providing a favourable environment for moisture convergence and intense monsoon precipitation. As Arctic warming accelerates under greenhouse gases (GHG), extreme precipitation events over South Asia are projected to increase,” the paper said.

Percentage increase in the intensity of intense precipitation events is much higher over the South Asian region as compared to global IPE.

“For 1-degree warming level, global IPE intensity increases by about 7%, while IPE intensity over South Asian region increases by approximately 20%. Similarly higher increase in the IPEs over the South Asian region as compared to global can be seen with increasing warming level,” the paper said.

HT reported on June 25 last year that India’s summer monsoon is undergoing significant changes, influencing not just agriculture—for which the rains are a lifeblood—but also the length and intensity of the summer.

Arctic sea ice reaches its minimum extent each September. September Arctic sea ice is now shrinking at a rate of 12.2% per decade compared to its average extent during the period from 1981 to 2010, according to the National Aeronautics and Space Administration.

“There is now a growing evidence that arctic sea ice melting can have serious impact on Indian monsoon. Both observations and model simulations suggest this relationship. It will affect both the mean and extremes. The pathways are through midlatitude atmospheric waves and increase in El Nino southern oscillation frequency,” former secretary, ministry of earth sciences, M Rajeevan said.