Human activity raised Indian Ocean temperatures around Australia over 40 last years

Australian researchers at the CSIRO have found a general warming of the ocean surface indicating the influence of rising atmospheric temperatures in the Indian Ocean region around Australia in the last 40 years.

Sydney, May 31 : Australian researchers at the CSIRO have found a general warming of the ocean surface indicating the influence of rising atmospheric temperatures in the Indian Ocean region around Australia in the last 40 years.

The team found a strong warming (about two degrees Celsius) over the last 40 years between 40 and 50 degree South latitude down to a depth of 800 metres. They also found sub-surface cooling in the tropics due to deep waters rising closer to the surface.

"The cooling is occurring between Australia and Indonesia where the Indonesian throughflow emerges into the Indian Ocean and is linked to the observed weakening of Pacific Ocean trade-winds," said Commonwealth Scientific and Industrial Research Organisation (CSIRO) oceanographer Dr. Gael Alory.

Dr. Alory said the research confirmed a long held view that temperature changes in the Pacific and Indian oceans could be partly explained by the effect of the "Indonesian throughflow" - a system of currents, which transports water between the oceans through the maze of straits and passages in the Indonesian Archipelago.

"From ocean measurements and by analysing climate simulations we can see there are changes in features of the ocean that cannot be explained by natural variability. These oceanic changes are almost certainly linked to changes in the heat structure of the atmosphere and have led to a rise in water temperatures in the sub-tropical Indian Ocean of around two degrees Celsius," said Dr. Alory.

"At the same time, we are seeing changes in ocean circulation in tropical regions as a result of a long-term weakening of the Pacific Ocean trade winds. This affects sea surface temperature in regions relevant to the source and distribution of rainfall across southern Australia," he said.

Dr. Alory said the change in atmospheric conditions altering ocean temperatures - weakening of Pacific Ocean trade winds and strengthening of westerly winds - could mostly be attributed to human activity.

The production of aerosols (tiny atmospheric particles), ozone depletion, and greenhouse gases, strengthening westerlies are related to changes in the Southern Annular Mode - an atmospheric feature similar to the El Nino Southern Oscillation and considered the dominant influence on Southern Hemisphere atmospheric variability, he said.

According to Dr. Alory, the models have helped them explain trends in the subtropical Indian Ocean temperatures and changes in relevant ocean features.

"In this area, the deep-reaching warming is due to a strengthening of westerly winds drawing a southward shift in ocean current patterns. These findings are consistent with research in the South Atlantic and South Pacific Ocean basins," said Dr. Alory.

The research appears in the journal Geophysical Research Letters.

ANI