A forest-fire requires oxygen, fuel and a heat source to burn. Air supplies the oxygen, flammable materials like trees, brush and grasses provide the fuel, and campfires, cigarettes, hot winds and the sun can provide the heat source that sparks the forest-fire.
Although most forest fires are started by human actions, nature produces the conditions that make a fire more likely. Once-green and moist vegetation is converted into flammable fuel by dry weather; strong winds carry fire rapidly over land; and combustion is encouraged by warm temperatures. When these factors are present, a single spark from lightning, a burning campfire or other source is all that is needed to ignite a wildfire that can ravage tens of thousands of acres and burn for weeks.
Since the mid-1980s, forest fires have become more common in the western United States and other areas of the world. Wildfires have occurred more than four times as often in recent years and have become more intense, burning seven times the amount of land as in previous periods. The increase in forest-fire intensity and frequency has been strongly linked to warmer temperatures caused by climate change. Previous research has focused on the effect that land-use practices have on wildfires, but recent studies show that the increased rate of fires is actually one of the first major indicators of global warming in the United States.
Climate change causes warmer spring and early summer temperatures, which in turn results in rapid snowmelt. In many regions, snow is melting earlier and faster in response to higher temperatures. The effect is that these areas become more dry overall, which increases the rate of forest fires. Researchers confirmed that more than half of the wildfires in the United States after 1980 occurred in areas that experienced an earlier-than-normal snowmelt.
Projections suggest that climate change will make areas that are already vulnerable to wildfires even more likely to experience the fires, and that the increasing intensity of fires can dramatically change forest composition. Forests are storehouses of carbon dioxide, a greenhouse gas that is largely responsible for global warming, and forest fires release the stored gas into the atmosphere. The additional carbon dioxide can lead to further global warming that will exacerbate the forest-fire problem even more.