Global warming 'could reawaken ancient climate pattern' with devastating impacts

Natural disasters such as Australia’s wildfires could become more common if global warming reawakens an ancient climate pattern similar to El Nino in the Indian Ocean, warns a new study.

Scientists say that if current warming trends continue an Indian Ocean El Niño could emerge as early as 2050.

El Nino is a climate cycle in the Pacific Ocean with a global impact on weather patterns; the cycle begins when warm weather in the western tropical Pacific Ocean shifts east towards the coast of South America.

Floods, storms and drought are likely to worsen and become more regular, disproportionately affecting populations most vulnerable to climate change.

Dr Pedro DiNezio, of University of Texas, said: ‘Our research shows that raising or lowering the average global temperature just a few degrees triggers the Indian Ocean to operate exactly the same as the other tropical oceans, with less uniform surface temperatures across the equator, more variable climate, and with its own El Niño.’

Computer simulations of climate change during the second half of the century show that global warming could disturb the Indian Ocean’s surface temperatures, causing them to rise and fall year to year much more steeply than they do today.

The seesaw pattern is strikingly similar to El Niño, a climate phenomenon that occurs in the Pacific Ocean and affects weather globally.

They discovered evidence of a past Indian Ocean El Niño hidden in the shells of microscopic sea life, called forams, that lived 21,000 years ago — the peak of the last ice age when the Earth was much cooler.

They analysed climate simulations, grouping them according to how well they matched present-day observations. When global warming trends were included, the most accurate simulations were those showing an Indian Ocean El Niño emerging by 2100.

Dr DiNezio said: ‘Greenhouse warming is creating a planet that will be completely different from what we know today, or what we have known in the 20th century.’

The latest findings add to a growing body of evidence that the Indian Ocean has potential to drive much stronger climate swings than it does today.

Co-author Professor Kaustubh Thirumalai, of University of Arizona, said that the way glacial conditions affected wind and ocean currents in the Indian Ocean in the past is similar to the way global warming affects them in the simulations.

Prof Thirumalai said: ‘This means the present-day Indian Ocean might in fact be unusual.’

The Indian Ocean today experiences very slight year-to-year climate swings because the prevailing winds blow gently from west to east, keeping ocean conditions stable.

According to the simulations, global warming could reverse the direction of these winds, destabilising the ocean and tipping the climate into swings of warming and cooling similar to El Niño and La Niña climate phenomena.

Prof Thirumalai said that disasters like monsoons could affect vulnerable populations that rely on rain to grow their food.

Oceanographer Michael Mcphaden, said: ‘If greenhouse gas emissions continue on their current trends, by the end of the century, extreme climate events will hit countries surrounding the Indian Ocean, such as Indonesia, Australia and East Africa with increasing intensity.

‘Many developing countries in this region are at heightened risk to these kinds of extreme events even in the modern climate.’

The findings were published in the journal Science Advances.

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