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El Niño Gives the World Gas
03.01.04
 

Earth globe showing sea surface temperatures associated with El Nino.
This image shows the warmer than normal sea surface temperatures(SST) and surface heights associated with 1997 El Niño. Red is warmer than normal and blue being colder than normal, and sea surface height anomalies are exaggerated heights. Credit: NASA

Cows do it. Horses do it. People do it after drinking soda, or while eating a spicy bowl of chili. They all pass gas. So does the Earth, especially during El Niño.

El Niño marks a major warming of the waters along the equator in the Pacific Ocean every 3 to 7 years and is characterized by shifts in "normal" weather patterns. Peruvians call it El NiƱo, "The Child," because this condition usually takes place around Christmas, celebrating the birth of Christ.

Scientists notice significant changes in the air during an El Niño year. Concentrations of two important greenhouse gases, methane and carbon dioxide, go up significantly. These gases are normally present as the product of burning fossil fuels like gasoline, oil or coal. Many scientists thought the increases in greenhouse gases during El Niño years were likely due to a changing balance of plant growth and death. However, new research is providing a different diagnosis to the source of the Earth's heartburn.

El Niño Gives Wildfires a License to Burn

Heavy smoke from wildfires during the 1998 El Nino

Sea-viewing Wide Field-of-view Sensor (SeaWiFS) on board the Orbview 2 satellite captured this image of the 1998 Mexico Wildfires.
Credit: NASA/Orbimage

Wildfires seem to ignite the geological version of the big belch. During El Niño, vast areas of the tropic regions dry out and become vulnerable to fire. During the 1997/1998 El Niño, wildfires ravaged huge areas in Latin America and Southeast Asia, belching large quantities of carbon dioxide (CO2) and methane into the air.

"We found that a large part of the [carbon dioxide] increases [were] the result of increased fire activity," said Guido R. van der Werf, of NASA's Goddard Space Flight Center.

For the first time, scientists have quantified the amount of greenhouse gases released during the 97/98 El Niño wildfires by combining satellite measurements and direct measurements of the air. They found that fire emissions of greenhouse gases increased across multiple continental regions in 1997-98, including Southeast Asia (60 percent of the global increase), Central and South America (30 percent), and boreal (northern) forests of North America and Eurasia (10 percent).

What's the Big Deal About Extra Gas?

Venus
Venus. Credit: NASA

Scientists worry that too much greenhouse gas in the atmosphere could warm the planet. Venus, with an atmosphere comprised of 95 percent carbon dioxide, is an extreme example of a planet with runaway greenhouse gases. The temperature on the planet's surface reaches about 896 degrees Fahrenheit (470 C), hot enough to melt lead. Luckily the Earth's oceans are like stomach medicine, absorbing extra carbon dioxide and preventing a runaway greenhouse effect. Plants are another carbon dioxide absorber, or as scientists call it, carbon sink.

Carbon_Cycle_Land
Click image to see animation of carbon cycle on land. Credit: NASA

Scientists are using this research to help understand the relationship between the carbon cycle and the climate system. The carbon cycle is the movement of carbon, in its many forms, through plants, animals, air, and oceans. The cycling of carbon affects the amount of carbon-based greenhouse gases in the atmosphere and thus the Earth's climate. This study shows how the intensity and variability of El Niño-induced droughts may impact carbon loss from the biosphere. Click on image to the right to see animation of the carbon cycle.



Plants, the First Suspect

Many scientists attributed the Earth's El Niño belch to changes in the balance between plant growth and death because the total yearly amount of carbon dioxide released by plants is about 20 times as much as the total amount of fire emissions around the world. "Gas emissions from fires would have to go up almost 100 percent to explain the growth rate from El Niño," says Van der Werf. "Most people didn't think that was possible."

World map of plant growth
Satellite image of vegetative growth around the world. Click image to see animation of plant growth around the world. Credit: NASA
The carbon dioxide concentration in the atmosphere is a function of it being taken out by plants when they grow, and released by microbes when they eat dead plant material.

"Our work indicates, the sum of these two processes has a smaller impact on atmospheric carbon dioxide levels than previously believed," said James Randerson of the University of California-Irvine, one of the study's authors.

During an El Niño it is relatively dry in the tropics, and plant growth decreases. Plants inhale carbon dioxide from the air. Decreased growth means there are fewer plants to breathe in carbon dioxide, therefore scientists thought the carbon dioxide growth rate during an El Niño was higher than usual.

Also, when plants die or shed their leaves, plant materials fall on the ground and decompose. Microbes eat the dead plants and exhale(CO2). "Microbes like wet and warm conditions, just like plants, so it is likely that during an El Niño less plant material is decomposed, which would mean that less carbon dioxide is released to the atmosphere, " said Van der Werf.

 
 
Rani Chohan
NASA Goddard Space Flight Center