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Post date: Oct 10, 2015 3:13:5 AM

How climate change will affect transboundary haze


6 Oct 2015

Discussions about the ongoing transboundary haze focus mainly on local and immediate causes. Topics include which agencies on Sumatra and Kalimantan are responsible for the fires directly causing the smoke, what can be done to punish transgressors and the transnational help offered within the Association of South-east Asian Nations (ASEAN) to assist Indonesian authorities in putting out the hot spots.

Something that has not featured prominently in the debate, however, is whether a changing climate influences the likelihood of future regional haze occurrences. Would future weather and climate over South-east Asia favour conditions that could lead to more frequent haze episodes? The latest climate research by regional scientists make for disquieting reading.

In our current climate, the haze often coincides with the dry Southwest monsoon season. This occurs from June to September, and the dry surface conditions enable local residents from provinces in Sumatra and Kalimantan to rapidly clear land either for subsistence farming, or for commercial palm oil and timber plantations. The prevailing winds then move the smoke over towards Singapore and Malaysia.

How would climate change caused by increased emissions of greenhouse gases affect the monsoon, in particular future temperature and rainfall patterns?

Average annual temperatures are all but certain to increase in all climate model simulations until 2100, but future average annual rainfall patterns throughout South-east Asia do not show a similar strong increasing trend.

However, seasonal changes in rainfall patterns are likely in the future because of projected increases in greenhouse gases in the atmosphere over the next century. Climate model simulations recently utilised and reported by the Centre for Climate Research Singapore indicate that less Southwest monsoon rainfall is expected. Worryingly, the projected future decrease in rainfall is clear over regions in Sumatra and Borneo where current hot spots are located, meaning these areas are likely to be drier.


There are two “natural” climate phenomena affecting South-east Asia — El Nino Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) —that may also be influenced by climate change, and these could consequently influence haze development.

A short primer: ENSO and IOD are periodic oscillations of sea surface temperature occurring in the equatorial Pacific and Indian Oceans, respectively. Under El Nino (or positive ENSO) conditions, historical rainfall over the Indonesian archipelago is decreased substantially. Likewise, positive IOD conditions, characterised by warmer-than-normal water in the western Indian Ocean, often results in a decrease of rainfall over Sumatra and Java.

The timing of these oscillations is important. In particular, the co-occurrence of these two during their positive phases during the Southwest monsoon could make already dry surface conditions even drier.

Research by Indonesia’s National Institute of Aeronautics and Space showed that both El Nino and positive IOD conditions simultaneously developed in 1997 and 2006. Both were years in which significantly drier-than-average conditions occurred over most parts of Indonesia during the Southwest monsoon. Unsurprisingly, significant haze that blanketed Malaysia and Singapore resulted during these periods.

Of note is that the current haze event also coincides with strengthening El Nino and positive IOD phases, and monthly rainfall in the associated Indonesian hot spot areas has significantly been lower than average for the past two months.

Therefore, the important question is, would future ENSO and IOD events be affected by climate change? Last year, two modelling studies by Australian-based researchers published in the academic journal Nature appear to indicate that occurrences of both phenomena are affected by global greenhouse gas warming.

The probability of these events occurring is considerably increased; the likelihood is doubled from one in 20 to one in 10 for the occurrence of strong ENSO, and trebled from one in 18 to one in six for strong IOD events occurring in the future.

Given the clear association of these phenomena with overall dry regional conditions, these are changing odds that could — and should — be of concern when considering transboundary haze development.


Thus, while we rightfully are concerned with the causes and impacts of the ongoing haze, let’s not neglect the elephant in the room that is climate change. There is evidence indicative of a future climate favouring more frequent transboundary haze episodes.

Stakeholders in ASEAN should tap this knowledge and adopt two approaches towards reducing the negative impact of haze. First, increase societal capacity in adapting to future haze events. For instance, authoritative and accurate health advisories can educate and inform affected people of the appropriate courses of action when air-quality thresholds are exceeded. Greater resources should also be devoted to treating heart- and lung-related illnesses that will increase with the onset of haze episodes, especially for people predisposed towards these ailments.

Second, the knowledge that business-as-usual greenhouse gas emissions can factor in more transboundary haze episodes must be considered by ASEAN governments at the forthcoming Climate Change Conference in Paris. Pledging carbon-curbing actions that limit global temperature increases would definitely help in mitigating the effects of climate change on the haze.

Hopes of stopping land burning — the root cause of the ASEAN transboundary haze — are hamstrung by political and cultural issues that engender no easy solutions. This situation is complicated by climate change. Instead, anticipating likely increases in future haze events and adapting accordingly could be a sensible, complementary and effective option for all affected stakeholders in the long run.

Lastly, there is a temptation to solely accuse climate change for a presumptive increase in haze events. This would be a mistake; it shows a misunderstanding of how regional climate change only promotes the ambient conditions enabling the haze, rather than being the root cause.


Dr Winston Chow is an urban climatologist working as an assistant professor in the Department of Geography, National University of Singapore. The views and opinions expressed in this essay are solely his own and do not express the views or opinions of his employer.