Wildfires have been more massive and dangerous over the years, occurring more frequently yearly. Now, researchers have found that human activity is one of the major factors why wildfires are spreading like never before.

A team from the University of Massachusetts analyzed records of each wildfire from 1992 to 2012 that needed intervention from firefighters. Among the 1.5 million wildfires, humans are to blame for an alarming 84 percent. This means that humans are causing almost half of all wildfires or 44 percent of all the burned acres in the last 20 years.

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Natural forces such as lightning strikes are still responsible for more than half of the burned acres of forest in the United States. However, researchers suggest that humans are expanding this "fire niche" and lightning cannot even reach some of these places that these wildfires start.

Humans have expanded this fire niche into areas that are historically known to experience a low number of lightning strikes.

Scientists have urged that wildfire prevention should focus on limiting human activity from further expanding this fire niche to areas that are normally not prone to lightning strikes and wildfires. Scientists also say that efforts have become more challenging to mitigate these wildfires especially in states within the Sun Belt. This region includes desert and semi-desert states from California to Texas to tropical states such as Florida.

Due to wildland and urban expansion, many are now living on the edges of wild lands which have become a major challenge for forest managers and federal agencies that are assigned to prevent and target wildfires. Researchers say that this area will double from nine to 18 percent by the year 2030.

According to Bethany Bradley from the University of Massachusetts in Amherst, people start a lot of fires from burning garbage or yard waste to accidental fires at home. However, past events linked to wildfires were driven by natural forces such as lightning strikes. Today, human ignitions have this extraordinary impact on national fire regimes.

Naturally occurring wildfires happen when lighting strikes, usually during the summer or when conditions are hot and dry. This new study revealed that manmade wildfires are happening outside fire season and more into fall and spring.

Also, researchers say that global warming is also increasing wildfire risks in many regions in the western states. Bradley explains that there has been a significant increase in human-ignited fire over time, most especially in spring. As spring seasons get warmer and earlier due to the effects of climate change, humans are endangering the environment to the most massive and dangerous wildfires ever.

This new study was published in the journal PNAS.