New Delhi: No direct link has been established between ocean warming and weakening of south-west monsoon, the government said Wednesday.
During the 1901-2012 period, the tropical Indian Ocean has experienced summer time warming of 0.7 degree Celsius, while the equatorial western Indian ocean experienced 1.2 degree Celsius of warming, Union Minister for Earth Sciences Harsh Vardhan said in a written response to Lok Sabha.
In response to a question on whether ocean warming has resulted in the weakening of south-west monsoon, the Minister said, "No direct link has been established so far."
"All Indian summer monsoon rainfall (AISMR), analysed for the period 1871-2014, has a typical epochal pattern of rainfall variablitiy with alternating periods of wet and dry monsoon (deficient rainfall) years.
"During such epochs, the monsoon was found to be less correlated with ENSO (El Nino Southern Oscillation). During the other periods like that of 1965-87, which had as many as 10 dry monsoon years out of 23, the monsoon was found to be strongly linked to the ENSO," Harsh Vardhan said.
ENSO refers to the effects of a band of a sea surface temperature which is warm or cold for long periods of time that develop off the western coast of South America. It is also known to cause climatic changes across the tropics and subtropics.
Indian Ocean Dipole (IOD), also known as Indian Nino, is an irregular oscillation of sea-surface temperatures in which the equatorial western Indian ocean becomes alternatively warmer and then colder than the eastern parts of the ocean.
"IOD and ENSO are independent climate modes, which frequently co-occur, driving significant inter-annual changes in terms of circulation within the Indian Ocean, influencing the monsoon variability," Vardhan said.