A recent study found that the effect of wildfires and burns on climate change is significantly worse than scientists previously believed.

While scientists were aware that wildfires and slash-and-burn agriculture had effects on both climate change and health, the effects have never been quantified.

Civil and Environmental Engineering professor Mark Z. Jacobson of Stanford University created a three-dimensional computer model to measure the exact effects of biomass burning on the climate. He found that the dangers, both to our environment and our health, are significantly worse than expected.

Looking at the effects on public health, Jacobson found that biomass burning causes 5 to 10 percent of global deaths resulting from air pollution.

"That means that it causes the premature deaths of about 250,000 people each year," said Jacobson.

He then analyzed the effects on the climate. It's known that forms of carbon emitted by burning, such as black carbon (soot), brown carbon and methane gas (CH4) are associated with global warming. Anthropogenic carbon dioxide emissions not caused by biomass burning account for 39 billion tons annually, but Jacobson and his colleagues showed that 8.5 billion tons, as much as 18 percent of non-burning emissions, are caused by biomass burning.

The study also goes so far as to implicate black carbon and brown carbon as significant culprits, rather than simply CO2 emissions. These carbon particles are important absorbing substances in our atmosphere that are released via biomass combustion and other high-temperature combustion processes.

Jacobson's research shows that these carbon particles allow burning to cause global warming by maximizing the fire's thermal impacts. Particles also enter water droplets that form clouds--these droplets are then penetrated by sunlight and when the carbon absorbs the light energy, heat is created and water evaporates, reducing relative humidity in the clouds. Eventually the clouds disappear and more sunlight (heat) hits the ground and seas, warming both.

Jacobson says another way black and brown carbon induce further global warming is by settling on snow and ice.

"Ice and snow are white, and reflect sunlight very effectively," said Jacobson. "But because carbon is dark it absorbs sunlight, causing snow and ice to melt at accelerated rates. That exposes dark soil and dark seas. And again, because those surfaces are dark, they absorb even more thermal energy from sunlight, establishing an ongoing amplification process."

Overall Jacobson calculated a planetary warming effect of 2 degrees Celsius over the span of 20 years. This effect is the summed result of anthropogenic greenhouse gases and warming caused by black and brown carbon emitted by wildfires, burning forests and savannahs for agricultural lands and slash-and-burn agriculture practices.

His research was published on July 30 in the Journal of Geophysical Research: Atmospheres.

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