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How Earth's infernos affect climate

Marcio Jose Sanchez / AP

Public information officer Theresa Mendoza walks on a ridge top as the Wallow Fire burns behind her outside of Eagar, Ariz., Wednesday, June 8, 2011.

At a glance, images of the forest fire raging in Arizona and the volcano erupting in Chile seem to suggest they are filling the atmosphere with gases and debris that will mess with the global climate, but experts say this week's events, in isolation, aren't much to worry about. 

The Willow fire in Arizona has charred at least 336,000 acres so far, filling the atmosphere with smoke, soot, and the greenhouse gas carbon dioxide. It joins a string of fires that have raged elsewhere in the U.S., including Texas and Florida.

The amount of greenhouse gases from these types of fires "can be quite substantial," Matt Hurteau, a forest ecologist at Northern Arizona University told me today. 

To illustrate how substantial, he pointed to work led by Christine Wiedinmyer at the National Center for Atmospheric Research in Boulder, Colorado, that shows forest fires in the U.S. between 2001 and 2008 accounted for six to eight percent of total annual U.S. greenhouse gas emissions.

One fire alone, however, is a blip compared to the emissions from burning fossil fuels such as oil and coal to power the global economy.

"A common misconception is that fire emissions are huge compared to fossil fuel emissions," Beverly Law, a forest ecologist at Oregon State University told me today. "They are not, really. Fossil fuel emissions trump everything."

Fire projections
But the fires burning in Arizona and elsewhere along the southern tier of U.S. do fit projections from models of global climate change that suggest the buildup of greenhouse gases in the atmosphere will cause the southwest, over the long term, to become drier, Law added.

"We just can't say there is a direct cause and effect right there," she said.

In fact, historical forest management decisions in Arizona play a major role in the severity of fires there, Hurteau said. In the ancient past, the ponderosa pine forests burned frequently and, as a result, were open and had a grassy understory. The grass, in turn, served as fuel for forest fires.

Beginning in the 1800s, pioneer settlers moved west and grazed the forests with their livestock, which reduced the fuels. Then, in the 1900s, a policy of fire suppression led to increased forest density. "Now we've got these really dense forests that are prone to this type of wildfire event," he said.

The effect of this management on forest fire ecology is independent of the climate signal. What's more, it is the weather on any given day that drives the severity of fire.

"To say that climate change is causing that weather on that day, we can't do that because climate is the longer term trend," Hurteau said.

Nevertheless, long term climate trends suggest the southwest will become drier, thus more prone to wildfire. More wildfire, in turn will put more greenhouse gases into the atmosphere, which should lead to more changes in the global climate, he noted.

Ho / Reuters

A plume of light-coloured ash stretches along the edge of the Andes in this natural-colour satellite image acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Terra on the morning of June 6, 2011, as the eruption at the Puyehue-Cordon Caulle volcano chain continues.

Volcanoes and cooling
Volcanoes, on the other hand, can potentially cool the climate by spewing the gas sulfur dioxide into the stratosphere where it blocks sunlight from reaching Earth, thus causing cooling. The eruption of the Puyehue-Cordón Caulle volcano in Chile, however, doesn’t appear to have done that.

"It wasn't a massive injection of SO2," Alan Robock, an environmental scientist who studies the connection between volcanoes and climate, told me today. "While it shut down air traffic over Argentina and Chile because of the ash, we won't be able to see the climate effect."

The last time a volcanic eruption cooled the climate was the 1991 eruption of Mt. Pinatubo in the Philippines, which caused global temperatures to cool by about half a degree Celsius for a couple of years.

The dramatic images of the Puyehue-Cordón Caulle show a giant ash cloud. The particles will fall out quickly, creating havoc locally, but they don't have a long-term climate effect.

A cooling effect will eventually comes from an explosive eruption that puts sulfur into the stratosphere, Charles Stern, a geologist at the University of Colorado at Boulder told me today.

"And that's good, we could use a little cooling right now," he said.

In fact, scientists have begun to discuss the idea of intentionally filling the stratosphere with sulfur to mimic the cooling effect of a Pinatubo-style eruption. Stern and Robock, though, said this geoengineering approach isn't a good idea due to the costs and other side effects.

"I think we are just going to have to wait for a volcano to do it," Stern said.

More stories on fires, volcanoes and climate change

John Roach is a contributing writer for msnbc.com. Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following msnbc.com's science editor, Alan Boyle, on Twitter (@b0yle).