The perennial problem of the haze has returned after a respite. The air quality has turned unhealthy for the first time since 2016, leading to stocks of face masks running out at some stores, Singaporeans cancelling their outdoor plans, and tourists lamenting the bad weather. These are familiar features of the environmental pollution, caused by forest fires, that wafts into Singapore, disrupting everyday life and resulting in economic damage. Unfortunately, what happens here and elsewhere in South-east Asia is also the result of an economic activity: burning to clear land for oil palm and paper plantations.

The 2015 haze crisis, the region's worst on record, provides a dire lesson in environmental economics. Its total cost on Singapore has been estimated at $1.83 billion, amounting to 0.45 per cent of the country's gross domestic product. Quite apart from the economic costs of disease, illness and early deaths, there are obvious social costs created by the sudden disruption to personal and family life. Although the haze now is not expected to be as severe as the 2015 crisis, it is right for the authorities to act pre-emptively by putting in place measures to ensure the health and well-being of the public, especially vulnerable groups such as the elderly, pregnant women, children, and people with chronic lung and heart diseases. Singaporeans have to ready themselves, unfortunately, for another phase of environmental uncertainty.