Widespread burning of lowland forests on Borneo as well as southern Sumatra is an annual, manmade occurrence. People use fires to manage agricultural lands which in this part of the world includes large palm tree plantations. Sometimes such fires escape management and burn out of control, resulting in damaging wildfires. Other wildfires ignite accidentally during activities like logging, or may be ignited naturally such as by lightning strikes in hot, dry conditions.
Because 2015 is an El Nino year, Indonesia is experiencing lower than average rainfall which may turn into a severe drought. Forests which are usually swampy dry out leaving behind a rich abundance of fire fuel in the form of peat, both intentional and accidental fires can quickly grow out of control. When peat dries out it is quite flammable and generates a huge amount of thick, dark smoke. Such heavy smoke produced by those fires contributes to the greenhouse gas emissions worldwide.
The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite captured this true-color image on September 10, 2015. The gray smoke is so heavy in some places that it completely obscures the land beneath.