Climate change and the Pacific

Atlantic warming causing stronger Pacific trade winds

SMH,

4 August, 2014

A mysterious surge in the trade winds that blow across the Pacific Ocean – one of the causes of a recent slow down in global temperature rises – is actually the result of the warming of the Atlantic Ocean, Australian-led research has found.

Research published in the journal Nature Climate Change on Monday sought to solve the puzzle of why the trade winds of the Pacific Ocean were about 50 per cent stronger since the late 1990s, levels above anything previous observed.

Previous research has identified the stronger trade winds as one cause of a pause in global surface temperature rises in the past 15 years, despite the large amounts of greenhouse gases being pumped into the atmosphere through human activity.

That research found the stronger winds were altering ocean overturning patterns and driving the missing heat deeper into the Pacific Ocean.

But the past work had not identified why the trade winds have been turbocharged in recent decades. In the latest research a team of international scientists, through the use of climate model experiments and observational data, found the warming of the Atlantic Ocean – which has occurred at least in part due to climate change – was the culprit.

‘‘It highlights how changes in the climate in one part of the world can have extensive impacts around the globe,” said Dr Shayne McGregor, a climate scientist from the University of NSW and lead author of the research.

As the Atlantic has warmed it has created a rising motion of air parcels due to the lower pressure on the ocean surface and higher pressure in the upper atmosphere over the region.

These rising parcels have been swept across the planet via upper atmospheric winds and eventually sink over the eastern Pacific creating higher surface pressure there.

The increased high pressure in the eastern Pacific give the trade winds an extra kick, because the winds blow from high to low pressure areas.

Climate change sceptics have used the pause in global surface warming in recent years to suggest climate change had stopped or had been overestimated by scientists.

But Dr McGregor warned that the changes in the trade winds that resulted in more heat being stored in the Pacific was not permanent. When the winds eased, he said, the storing effect would slow and could bring up heat from the ocean, which would result in an acceleration of surface temperature rises.

‘‘The time scales we are talking about are 15-30 years. We think it is a matter of time until the heat that is being pushed down will be brought back up,’’ he said.

Despite the pause, global surface temperatures have remained well above long-term global averages. 2013 was the sixth hottest year on record, and 13 of the 14 hottest years have occurred since 2000.

The strengthened Pacific trade winds have also amplified drought in California, caused the tropical eastern Pacific Ocean to cool and sped up sea-level rise in the western Pacific.

Meanwhile in separate research, also published in Nature Climate Change on Monday, scientists have found unchecked global warming will amplify damaging El Nino weather events – linked to devastating natural disasters and lower rainfall in Australia – until 2040, but after that the increased intensity may fall away.