Climate change signal detected in the Indian Ocean

May 30, 2007

The signature of climate change over the past 40 years has been identified in temperatures of the Indian Ocean near Australia.

"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," said CSIRO oceanographer Dr Gael Alory.

"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.

"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," Dr Alory said.

The research – by Dr Alory, his CSIRO Wealth from Oceans National Research Flagship colleague, Dr Gary Meyers, and CSIRO Marine and Atmospheric's Dr Susan Wijffels – has recently appeared in the journal, Geophysical Research Letters. The paper examines trends in Indian Ocean temperatures over 40 years that can help scientists and resource managers understand fluctuations in rainfall patterns over southern Australia.

The research, contributing to the Australian Climate Change Science Program and partly funded by the South East Australia Climate Initiative, combined access to ocean observations using the volunteer 'ships of opportunity' program and a set of models used by scientists in developing the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment. Thanks to the operators and crew of commercial ships, Australian scientists have access to a regular series of ocean measurements to a depth of 800 metres across the Indian Ocean.

The team's key findings were:
-- a general warming of the ocean surface indicating the influence of rising atmospheric temperatures;
-- a strong warming (about 2°C over 40 years) between 40°S and 50°S down to a depth of 800metres;
-- and, sub-surface cooling in the tropics due to deep waters rising closer to the surface.

Dr Alory says the research confirmed a long-held view that temperature changes in the Pacific and Indian oceans can 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.

"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," he says. The models also helped to 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.

He said that the change in atmospheric conditions altering ocean temperatures – weakening of Pacific Ocean trade winds and strengthening of westerly winds – have been mostly 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.

Dr Alory said climate models used in the IPCC Fourth Assessment show that changes in westerly wind patterns are expected to intensify in a global warming scenario and to accentuate the southward shift in sub-tropical ocean circulation patterns.

Source: CSIRO Australia

Explore further: Future heat waves pose risk for population of Greater London

add to favorites email to friend print save as pdf

Related Stories

Japan cancels next Antarctic whaling hunt after ICJ ruling

Apr 03, 2014

Japan said Thursday it was cancelling its annual Antarctic whaling hunt for the first time in more than a quarter of a century in line with a UN court ruling that the programme was a commercial activity disguised ...

Flight 370 search shifts after new look at data

Mar 29, 2014

Three weeks into the mystery of Flight 370, investigators relying on newly analyzed satellite data shifted the search zone yet again, focusing on a swath of Indian Ocean where better conditions could help ...

Recommended for you

Australia's dirty secret: who's breathing toxic air?

1 hour ago

Australians living in poorer communities, with lower employment and education levels, as well as communities with a high proportion of Indigenous people, are significantly more likely to be exposed to high ...

Predicting bioavailable cadmium levels in soils

19 hours ago

New Zealand's pastoral landscapes are some of the loveliest in the world, but they also contain a hidden threat. Many of the country's pasture soils have become enriched in cadmium. Grasses take up this toxic heavy metal, ...

Oil drilling possible 'trigger' for deadly Italy quakes

23 hours ago

Italy's Emilia-Romagna region on Tuesday suspended new drilling as it published a report that warned that hydrocarbon exploitation may have acted as a "trigger" in twin earthquakes that killed 26 people in ...

Snow is largely a no-show for Iditarod Trail Sled Dog Race

23 hours ago

On March 1, 65 mushers and their teams of dogs left Anchorage, Alaska, on a quest to win the Iditarod—a race covering 1,000 miles of mountain ranges, frozen rivers, dense forest, tundra and coastline. According ...

User comments : 0

More news stories

Melting during cooling period

(Phys.org) —A University of Maine research team says stratification of the North Atlantic Ocean contributed to summer warming and glacial melting in Scotland during the period recognized for abrupt cooling ...

Warm US West, cold East: A 4,000-year pattern

Last winter's curvy jet stream pattern brought mild temperatures to western North America and harsh cold to the East. A University of Utah-led study shows that pattern became more pronounced 4,000 years ago, ...

Australia's dirty secret: who's breathing toxic air?

Australians living in poorer communities, with lower employment and education levels, as well as communities with a high proportion of Indigenous people, are significantly more likely to be exposed to high ...