By Keith Ridler, Associated Press 

BOISE, Idaho — A new study on Western forest fires confirms what is already apparent — wildfire seasons are getting longer and more destructive.

But researchers with the University of Idaho and Columbia University also say humans are to blame for much of that increase.

The study says human-caused global warming contributed an additional 16,000 square miles of burned forests from 1984 to 2015.

Researchers say the 16,000 square miles represent half of the forest areas that burned over the last three decades.

The study found that longer and hotter dry spells are causing Western forests to dry out and become more susceptible to wildfires over a longer period of time.

The study says the trend is likely to continue for decades while there are enough trees to fuel the flames.