Every year an average of more than 38,000 wildfires ravage 5 million acres of land in the U.S. In recent years, fires have blackened as much as 9 million acres, consuming everything in their paths.

So far this year more than 22,000 blazes have required more than 13,000 firefighters, 24 of whom have died. The fires have burned to the ground more than 1,150 homes and businesses and scorched nearly 1.6 million acres while consuming an estimated $546 million out of the $790.5 million 2013 federal wildfire suppression budget.

Even so, the blackened area is well below the 10-year average of 2.4 million acres burned as of this date.

As of Tuesday nearly 490,000 acres of wildfires raged through the American West. In Colorado nearly 100,000 acres were ablaze in the Western Rockies as the Black Rock fire threatened Colorado Springs environs. It was contained by firefighters June 21 following a nine-day battle after it had destroyed 509 homes and placed 38,000 residents under evacuation orders.

The fire outside Prescott, Ariz., that took the lives of 19 firefighters earlier this week had burned 13 square miles by Wednesday. Officials hoped to allow residents back into their homes this weekend and contain the fire by July 12, according to the Associated Press.

Firefighters have to work with three elements of fire, called the fire triangle: fuel, oxidant and heat. In wildfires, lightning often ignites the carbon-based fuel of wood, grass and brush, but humans are responsible for 4 out of 5 fires either by accident or by arson.

Blocking any one of the three elements of the triangle will snuff the fire. The bigger the fire, the more difficult it is to contain — whether by clearing fire lanes or lighting backfires to reduce available fuel, or dumping retardant or water to asphyxiate and cool the blaze.

Large wildfires create their own weather. Heated air causes a powerful updraft that draws air in horizontally from around the area of the fire and sends it up, where condensation creates massive thunderstorms. The ensuing rain may help dampen the fire, but in many cases the associated lightning starts even more fires.

The chemical reaction of energy-rich cellulose stored in the wood from years of photosynthesis unleashes tremendous amounts of energy as it dumps millions of tons of soot, carbon dioxide and other gases into the atmosphere. A typical wildfire releases 220 megawatts of energy per acre burned. For the 1.6 million acres burned so far this year, that amounts to 334 million megawatts, equivalent to about 1 percent of U.S. annual energy consumption.

To satisfy U.S. annual energy consumption by burning forests would require using 160 million acres of timber, an area about the size of Texas.

Although carbon emissions from global wildfires vary substantially from year to year, they amount to 20 percent to 40 percent of those from fossil-fuel combustion and cement production, the two largest man-made sources of carbon input.

Global warming is not caused by wildfires, but their emissions are another factor that must be considered in the complexity of global climate models.

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Richard Brill is a professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.