English: A pall of gray smoke from many dozens of fires hung over Southeast Asia in late February 2021.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra satellite acquired a true-color image of the smokey scene on February 24. Each red “hot spot” marks an area where the thermal bands on the MODIS instrument detected high temperatures. When combined with typical smoke, such hot spots are diagnostic for actively burning fire.

The number of fires, their location along forest edges and in non-forested land, and time of year all suggest that most of the fires agricultural in nature. Using fire to manage agricultural land, or to clear forests for use as cropland or pasture, is a traditional tool used for agriculture in many places in the world, including Southeast Asia. The countries that have fires burning include (clockwise from left), Burma (Myanmar), Laos, Vietnam, Cambodia, and Thailand.

Smoke, especially if heavy or long-standing, can negatively impact the health of humans and animals. In addition, vegetation fires may release greenhouse gases such as carbon dioxide, carbon monoxide, nitrous oxide, methane, non-methane hydrocarbons and other chemicals, including aerosols. Each of these can impact radiative budget, air quality and health both locally and in the region.