Satellite images may offer clues on global warming

April 25, 2001
Web posted at: 1:57 PM EDT (1757 GMT)

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(CNN) -- A sensor that has been aboard NASA's OrbView-2 spacecraft since 1997 observing plants and algae worldwide may offer unprecedented insight into how Earth functions and improve models that predict global climate change, scientists said.

"There has been very clearly a warming in the climate over the last 20 years or so," said Jorge Sarmiento of Princeton University. "It is very difficult to clearly attribute any given warming trend to any specific cause."

The researchers, who recently published their findings in the journal "Science," studied three years of data from the Sea-viewing Wide Field-of-View Sensor (SeaWiFS) -- the first single instrument to observe the global carbon cycle by monitoring carbon intake of plants and algae.

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The satellite images use color shading to demonstrate the flow of plant life on Earth: blue for areas that are void of plant activity; red for areas with an over-abundance of plant activity and green for areas where plants are thriving.

Plants and algae use chlorophyll in photosynthesis, during which they absorb carbon dioxide from the atmosphere and ocean. The process plays a critical role in regulating atmospheric carbon dioxide.

According to the data, the land's plants and ocean's algae are devouring carbon dioxide at record rates in recent years -- from 111 billion metric tons in 1997 up to 117 billion metric tons, according to NASA researchers.

Ocean algae accounted for most, if not all, of the increased carbon dioxide intake during the study. Land plants exhibited no such global trend, although some areas experienced noticeable changes. The scientists remain puzzled by some of the observations.

The initial increase was largely due to the plants' response to a strong El Nino to La Nina transition in 1998, said the scientists.

El Nino and La Nina refer respectively to the periodic warming and cooling of the Pacific Ocean. The complimentary weather patterns can each last several years or longer.

These weather patterns can dramatically affect the severity and number of extreme weather events across the world -- including droughts, hurricanes and rainstorms -- and disrupt the food chain in the oceans.

The cause of the continued increase after the transition to La Nina is not yet known.

"We can see seasonal changes in plant and algae chlorophyll levels very well," said lead author and NASA oceanographer Michael Behrenfeld in a statement. "But we don't have a long enough record to distinguish multi-year cycles like El Nino from fundamental long-term changes caused by such things as higher carbon dioxide levels in the atmosphere."

Oceanographers have also used SeaWiFS to study the migration patterns of turtles, deadly blooms of algae and the long-range movement of air pollution. NASA plans to produce a five-year study using data from SeaWiFS and two sibling satellites, Terra, which was launched in December 1999, and Aqua, which is scheduled for launch in late 2001.

CNN's Richard Stenger and Ann Kellan contributed to this report.