Global warming can trigger extreme Pacific weather, says study
[MANILA] Global warming is likely to alter rainfall patterns in East Asia and the Pacific, causing more intense drought and floods in decades to come, according to a study published in Nature last month (15 August).
A team of Australian-based scientists estimated that increased greenhouse gas emissions in the atmosphere will enhance equatorial Pacific warming by two degrees Celsius by 2050.
This will cause the South Pacific Convergence Zone (SPCZ) — the Southern Hemisphere's most expansive rain band, which extends from the sub-equatorial western Pacific south-eastwards to French Polynesia — to move northwards towards the equator by 1,000 kilometres.
Normally, the rain band moves just a few kilometres northwards or southwards. During events such as El Nino and La Nina, the movement is 200–300 kilometres.
The scientists project that the frequency of such occurrences will almost double over the next 100 years, and could lead to extreme climate events, such as droughts, floods and tropical cyclones, with a potentially devastating impact on countries in the Pacific.
In an interview with SciDev.Net, Wenju Cai, the CSIRO (Commonwealth Scientific and Industrial Research Organisation) oceanographer who led the study, said that the last time SPCZ moved northwards by up to 1,000 kilometres was in the years 1997 to 1998.
This extreme shift led to an intense El Niño, a warm water current that periodically flows along the coast of Ecuador and Peru, greatly affecting wind, sea surface temperature, and precipitation patterns in the tropical Pacific. In 1997-1998, this had the effect of parching lands in South-East Asia, destroying crops and causing dire food shortages. It also brought cyclones to regions, including French Polynesia, which were unaccustomed to such events.
"Greenhouse gases in the atmosphere are causing a global redistribution of rainfall away from the subtropics to higher latitude regions," said Elisabeth Holland, a professor of climate change at the University of South Pacific in Fiji.
If the rain band moves north-eastwards by 300 kilometres, countries located within the bands' normal position — such as Vanuatu, Samoa, and the Southern Cook Islands — will experience cyclones, droughts and forest fires.
As the band moves further up, it will also bring floods and drought to South-East Asia and the rest of the western Pacific region, Cai said.
He warned that regional policymakers should heed the SPCZ when preparing climate change adaptation programmes.
Governments should ensure that any infrastructure built over the next few years would have the capacity to withstand the stronger typhoons, Cai added. He also advised that farmers need to be prepared for longer and more intense droughts and typhoons.
Holland said these warnings should give more impetus to plans to reduce greenhouse gas emissions more extensively than directed by the current trajectory, particularly in light of China and India's escalating emissions, coupled with the slow decrease in Europe and the United States.
This article has been produced by our South-East Asia and Pacific news desk.
Nature doi:10.1038/nature11358 (2012)