Australian scientists have identified causes of a rapid warming in the upper subtropical oceans of the Southern Hemisphere.
They partly attribute the observed warming, and preceding cooling trends to ocean circulation changes induced by global greenhouse gas emissions and aerosols predominantly generated in the Northern Hemisphere from human activity.
The research, by scientists from CSIRO and the University of NSW, was published today in Scientific Reports.
Mr Tim Cowan, lead author of the study, says his group was initially interested in the three decade long cooling below the surface of the Southern Hemisphere subtropical oceans from the 1960s and 1990s. "But what really caught our eye was a rapid warming of these subtropical oceans from the mid-1990s, most noticeably in the Indian Ocean between 300 m to 1000 m depth," said Mr Cowan.
This had the research team asking whether this rapid warming was partly a response to greenhouse gases overcoming the cooling effect of aerosols that peaked globally in the 1980s due to the introduction of clean air legislation across United States and Europe.
To test this, the researchers examined more than 40 state-of-the-art climate simulations that included historical changes to greenhouse gases and aerosols over the twentieth century. "What we found was that the models do a good job at simulating the late twentieth century cooling and rapid warming in the subtropical southern Atlantic and Pacific Oceans, however they show an around 30-year delay in the warming in the Indian Ocean" said Mr Cowan.
"This delay in the modelled Indian Ocean warming is likely due to the presence of atmospheric aerosols, generated through transport emissions, biomass burning, and industrial smog, together with natural emissions of sea salt and dust - these were also the main cause of the late twentieth century subtropical Indian Ocean below-surface cooling" said Mr Cowan.
|Contact: Craig Macaulay|