Food for thought in climate change

Given my ignorance of climatology and the earth sciences in general, I have always found the climate change debate a little too hot to handle. It has become, as one of my friends puts it, the ideological equivalent of the old battle between Marxism versus capitalism.

But now that I've decided to dip my toe in, I have to say that what really bothers me is this: What if the naysayers are dead wrong and the process - perhaps over the next few decades or another century - arrives at the point where it is, in fact, too late to reverse.

Who will be able to say: "I told you so?" Worse than that, Fox Television's right-wing ranter Sean Hannity, someone I watch occasionally for a dose of horrid fascination, will go to his grave still thinking he was right, like all the other neo-cons.

No one who knows me would call me a liberal. But I do believe the climate is changing in very strange ways. I am reminded of that once again as I sit here with monsoonal rain pounding down in the middle of the so-called dry season.

That's why my attention was drawn to a new study, published in the journal Nature Geoscience, in which American, Indonesian and Australian scientists say the picture is not encouraging.

The 10-year study shows that the current pushing warm waters from the Western Pacific into the Indian Ocean through the Indonesian archipelago's network of often narrow straits is acting differently and could transform the climate in both ocean basins as a result.

What makes all this interesting is the Indonesian seas are the only tropical location in the world where two oceans interact in this manner, with the throughflow playing a role in everything from Indian monsoons to the El Nino Southern Oscillation (ENSO) weather phenomenon.

The main inflow passage through the archipelago is the broad Makassar Strait, which separates Borneo from Sulawesi. Some water then goes on to enter the Indian Ocean through the Lombok Strait, between Lombok and Bali, while the bulk flows east through the Banda Sea and out through the Ombai Strait and Timor Passage.

Secondary portals channel water from the Western Pacific into the Sibutu Passage, which connects the Sulawesi Sea to the Philippines' Sulu Sea, and from the South China Sea via the Karimata Strait, north of Singapore.

According to the scientists, the so-called Indonesian Throughflow (ITF) linking the Pacific Ocean to the Indian Ocean is acting differently because of climate changes. The strongest currents have become shallower and faster.

That suggests to them that human-caused climate change could worsen the effects of El Nino and its wet sister, La Nina, which are arriving with increasing frequency. The changes also affect what nutrients get delivered to marine organisms in the region and in what quantity.

The 1990s in Indonesia were characterised largely by sustained El Nino conditions - particularly towards the end of the decade - which then changed to large swings between El Nino and La Nina conditions in the 2000s.

Indonesians will remember La Nina during 2010-2011, when the cooling of the Pacific meant they did not have a dry season at all. So will people in hapless Queensland, which was deluged with rain for eight straight months and saw the worst flooding on record.

Now, coincidentally, we are awaiting the return of another El Nino, late next month. During this phenomenon, trade winds weaken and the surface water being driven across the central and eastern Pacific becomes progressively warmer because of its longer exposure to solar heating.

With those warmer waters migrating eastwards - and eventually affecting marine life along the South American coast - the result is less atmospheric moisture and less rainfall across Indonesia and Australia.

The worst examples occurred in 1997-98. With rainfall well below the 10cm average for the months of March and April, a year-long drought set in, triggering calamitous bushfires across Kalimantan and Sumatra as farmers sought to replace depleted food crops.

Singaporeans will recall that period. They are likely to be given yet another annual reminder in the coming months, with a new El Nino on the oceanic doorstep and Indonesia's disaster agency already warning of a huge increase in fires in Sumatra.

"Changes in the amount of warm water that is carried by the ITF will affect the sea surface temperature and thus shift the patterns of rainfall in the whole Asian region," lead researcher Janet Sprintall, from the Scripps Institution of Oceanography at the University of California San Diego, told The Straits Times.

She says numerical simulations that include the mixing of the flow through the Indonesian seas show a much cooler sea surface temperature, with reduced rainfall, compared with those that do not include this flow.

This means wind changes over Indonesian waters that could reduce the strength of El Ninos, but increase the variability of the Indian Ocean Dipole (IOD). In this alternating oscillation, surface temperatures become warmer in the western part of the ocean and then colder in the eastern part.

Dr Sprintall believes the seasons as we know them could be turned on their heads over the next few decades - with everything that will mean for agriculture and fisheries in Indonesia and neighbouring countries.

When the IOD is in its negative phase, as it was in 2010, you get very warm surface temperatures south of Java and heavier rainfall across the country. In other words, it only amplified La Nina's stronger regional precipitation.

All food for thought - even if none of us will be around if and when the time comes for climatologists of the future to say: "We told you so."

Asia-wide shifts

Changes in the amount of warm water that is carried by the Indonesian through flow will affect the sea surface temperature and thus shift the patterns of rainfall in the whole Asian region.
- Dr Janet Sprintall of the Scripps Institution of Oceanography at the University of California San Diego

This article was first published on JULY 7, 2014.
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