Indonesia is currently experiencing the annual dry season, thus making forests more vulnerable to fires (although global climate changes have made the dry/wet season distinction somewhat unclear in recent years in Indonesia).

Five provinces have declared emergencies as the forest fires are spreading. While on Sunday satellite images showed that the number of fires was 150, it had risen to 179 fires by Tuesday. In Aceh (Sumatra) dozens of people are being treated for lung infections as a result of the choking smoke, while some schools have temporarily closed their doors.

Forest fires are believed to be caused by people's traditional slash-and-burn method to clear forest for the establishment of a plantation (usually for palm oil and pulpwood plantations). Although it is an illegal act, weak law enforcement in Indonesia facilitates this devastating habit.

In 2015 man-made forest fires on Sumatra and Kalimantan caused one of the world's biggest ever natural disasters. Based on a World Bank report - released in December 2015 - some 100,000 man-made forest fires destroyed about 2.6 million hectares of land (between June and October 2015) and caused toxic haze to spread to other parts of Southeast Asia, giving rise to diplomatic troubles. This disaster is estimated to have cost Indonesia IDR 221 trillion (approx. USD $16 billion or 1.9 percent of the country's gross domestic product). Moreover, researchers from Harvard and Columbia universities in the United States estimated that the toxic haze may have caused over 100,000 premature deaths.

Read also: Overview of Natural Disasters in Indonesia

Meanwhile, a study published in Scientific Reports, conducted by scientists at King's College London in cooperation with the Center for International Forestry Research (CIFOR), says the 2015 forest fires on Sumatra and Kalimantan released some 11.3 million tons of carbon each day (a figure that exceeds the 8.9 million tons of daily carbon emissions in the European Union).