Wildfire is a natural process that affects Earth’s surface and atmosphere, and humans have coexisted with fire since our emergence. Today, however, we face a global landscape of growing wildfire risks – which many believe are accelerated by climate change.

The fires of 2019-2020 burned at massive scales and impacted human communities, wildlife, and the environment. The wildfires that took place around the world had a variety of causes, ranging from human carelessness (discarded cigarettes, unattended campfires, sparking powerlines) to land-use practices (deforestation and slash-and-burn methods) to environmental stressors such as drought and invasive species, including eucalyptus and gamba grass.

All wildfires require three key components: fuel, heat and oxygen. Basically, they burn when oxygen mixes with some sort of plant material that’s been heated to its flash point — the lowest temperature at which it ignites. The resulting chemical reaction produces the fire’s visible and invisible products, including carbon dioxide and water, which warm the air and feed the flames.

Wind, temperature and humidity also impact how fast a wildfire spreads. For example, when there’s a lot of wind and dry conditions, vegetation has less moisture content, making it more flammable. When hot, dry air rises, it preheats fuel further uphill, allowing the fire to advance faster.

All these factors make it easier for wildfires to start, spread, and grow out of control, causing significant impacts on communities and the environment. As fires grow, they create a smoke plume that can harm human health, trigger respiratory illnesses, and contribute to climate change when the burned plants release greenhouse gases.