Rapid Indian Ocean warming affecting marine plankton, fish stocks

The ocean heat uptake has doubled since 1997 resulting in warmer surface layers of the oceans, as well as increasing ocean warming at greater depths. One of the symptoms of this can be seen in the rapid warming of the Indian Ocean. This ocean has the largest warming trend in sea surface temperatures in the tropics over the past century. This has resulted in a 20 per cent reduction in primary plankton productivity for the period 1998 to 2013, contributing to reduced fish stocks and adding a threat to food security.

Indian Ocean Dipole set to triple frequency of floods, bushfires and droughts

Climate change and extreme weather is likely to hit the Indian Ocean rim countries much harder over the coming century. That is the conclusion of a new study lead by CSIRO climate scientist Wenju Cai.

The research lead by Wenju Cai from CSIRO's Marine and Atmosphere Division outlines that an increase in greenhouse gases and climate change is likely to cause more extreme positive Indian Ocean Dipole (IOD) events to occur and that this will likely triple the frequency of bushfires, floods and drought in Australia, Africa and India from one event every 17 years to one every 6 years.

The interaction between ENSO and IOD still needs much more research and study to understand. IOD events are often triggered by El Nino, but can also sometimes occur during La Nina years as well.

Dr Wenju Cai told the ABC:

"Most of our severe bushfires were preconditioned by the Indian Ocean Dipole... When a summer season is preceded by an [extreme positive] Indian Ocean Dipole our bushfires tend to be much more severe.

"Now this is in Australia, but it has global impact. [For example] in Indonesia, a positive Indian Ocean Dipole tends to cause drought. You may recall in 1997 we had a wild bushfire in Indonesia... emitting a lot of pollutants and smoke that caused health problems to many millions of people in the region and also cost lost economic activity because people couldn't go out because of the visibility problem.

"In the meantime, in eastern African countries, they experienced devastating floods, causing thousands to die... and displacement of many hundreds of thousands."

Extreme Weather: Cyclone Thane hits India

One of the last tragic extreme weather events of 2011 was Cyclone Thane hitting the Tamil Nadu coast of India. It caused 46 deaths and damaged buildings, roads and crops. It was the strongest tropical cyclone of 2011 within the North Indian Ocean.

Image from NOAA - Cyclone Thane in the Bay of Bengal
on 28 December 2011, taken by Meteosat

From the Bay of Bengal it made landfall as a very severe cyclone on Friday 30 December very close to Puducherry. The storm struck with torrential rains and gale force winds from 125 to 140 kilometres per hour which uprooted hundreds of trees and knocked down electric poles and mobile phone towers producing power outages and communications blackouts in several areas.

A recent study linked increasing air pollution over the Indian sub-continent to an increase in the intensity of Tropical cyclones in the region.

Cyclone Intensity in North Indian Ocean linked to increasing air pollution

A recent study linked increasing air pollution over the Indian sub-continent to an increase in the intensity of Tropical cyclones in the Arabian Sea. The air pollution over the Indian sub-continent changes wind circulation patterns reducing wind shear in the Northern Indian Ocean providing more potential for intense cyclones to form. This is combined with warm sea surface temperatures in the region, especially in the Bay of Bengal, to provide the conditions for more intense and destructive cyclones.

Image by NASA Earth Observatory - Category 4
Tropical Cyclone Gonu in the Arabian Sea in 2007