It increasingly appears that weather systems over Asia are interlinked and feeling the effects of El Nino, global warming and local air pollution

Despite intense floods in some parts of India, the monsoon rainfall across India through August 10 is only 91% of average rainfall, a quarter of the country is now rain deficient, according to the latest meteorological data, and the monsoons should start withdrawing from northwest India this week.

The strongest El Nino-Southern Oscillation (ENSO)–a coupled ocean-atmosphere system in the Pacific Ocean that influences, among other weather events, the monsoons–in 17 years and human-induced global warming have significantly contributed to the severity of the recent weather. These include heat waves and floods, not just in India but its neighbourhood, according to scientists.

These events–recently, a typhoon last month in Taiwan and record high temperatures in Hong Kong–appear unconnected, but it appears increasingly apparent that weather systems over Asia are interlinked and feeling the effects of three phenomena: El Nino, global warming and local air pollution.

Heat waves occur over land and also over oceans, and typhoons are controlled by ocean temperatures. While El Nino triggers variations from year to year, global warming makes the consequences worse. This year, the planet has experienced the highest average temperatures in 136 years of record keeping.

“In general the climate is changing because of human influences changing the composition of the atmosphere and leading to global warming,” said Kevin Trenberth, Distinguished Senior Scientist at Climate and Global Dynamics, National Center for Atmospheric Research, in the US city of Boulder. “The atmosphere is generally warmer and moister as a result.”

Interconnections are typified by the typhoon Soudelor, which slammed Taiwan on August 9 and swept into China as a tropical storm.

“Sometimes local heat can be intensified around the edges of a typhoon, where air is sinking in response to the rising air within the typhoon itself,” said Bob Henson, a meteorologist and blogger for Weather Underground and the author of The Thinking Person’s Guide to Climate Change.

“This process taking place around the periphery of Typhoon Soudelor probably helped lead to the all-time record high observed in Hong Kong (37.7°C on August 9), as well as the sustained very hot temperatures in Japan,” said Henson.

Record global heat, the El Nino effect and global warming

All weather events, Trenberth observed, are “in the context of large natural variability (that) we call weather and climate variability.” These weather events would occur anyway because they are natural phenomena. With global warming, their effects and consequences are often worse: the heat is greater, the rains are heavier.

Already, it has been a very warm year for earth as a whole, said Henson. Global temperatures are at a record high for January through July for the planet (land and ocean), in records that go back more than a century, manifesting as heat waves.

As for the El Nino event currently underway, its scale is substantial and has led to a much warmer Pacific, resulting in more typhoons and related weather events. The Climate Prediction Center in Maryland, U.S reported in its update on August 31 that the sea surface temperature as measured by the Nino 3.4 index for the previous week was 2.2 degrees above average, reflecting the influence of El Niño.

“El Nino has large-scale patterns associated with it, affecting all Pacific-rim countries always, but extending much farther for large events as we have now,” said Trenberth. “It helps determine where the rains occur and where the droughts, heat waves and wild fires are more likely.”

Although typhoons, such as Soudelor, can develop from small atmospheric disturbances, they feed on the warm waters of the Pacific and the associated water vapour in the atmosphere.

“But not every typhoon will be wetter just because the overall climate is warming,” said Henson. “It is critical to recognise that climate change does not cause a weather event like a typhoon. Instead, it changes the overall atmosphere in which these natural weather events take place.”


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Source: September 8, 2015, Business Standard