Another El Nino problem: More carbon dioxide in air

SETH BORENSTEIN, AP Yahoo News 12 Oct 17;

A new NASA satellite has found another thing to blame on El Nino: A recent record high increase of carbon dioxide in the air.

The super-sized El Nino a couple of years ago led to an increase of 3 billion tons of carbon in the air, most from tropical land areas. The El Nino made it more difficult for plants to suck up man-made carbon emissions and sparked fires that released more carbon into the atmosphere.

The effect was so large that it was the main factor in the biggest one-year jump in heat-trapping gas levels in modern record, NASA scientists said.

Scientists have long known that carbon dioxide levels spike during an El Nino, the natural occasional warming of parts of the central Pacific that causes droughts in some places, floods in others and generally adds to warmer temperatures worldwide.

Data from NASA's Orbiting Carbon Observatory-2, which was launched in 2014, provides more specifics on how that happens and by continent.

Researchers found that in drought-struck parts of South America plants grew less, there were more fires in Asia, and there was an increased rate of leaf decay in Africa. The findings were published Thursday in the journal Science.

That 3 billion tons of carbon, while significant, is still dwarfed by the 10 billion tons a year that comes from the burning of coal, oil and gas, said Scott Denning, a Colorado State University atmospheric scientist.

Study co-author Annmarie Eldering, NASA's deputy project scientist for the satellite, said the new results show how El Nino can counteract efforts to reduce carbon emissions.

Human-caused carbon dioxide emissions were roughly flat in 2014, 2015 and 2016, but National Oceanic and Atmospheric Administration figures show that 2015 saw a rise in carbon in the air 3.03 parts per million, the largest since scientists started tracking emissions in Hawaii in 1959.

Normally about 25 percent of the human-caused carbon emissions are sucked up by plants on land, but during this powerful El Nino that was only 5 percent, said Junjie Liu, a NASA scientist and study lead author.

Oceans took out more than normal amount of carbon out of the atmosphere, but it wasn't enough to compensate for the land deficit, Eldering said.

Jonathan Overpeck, a University of Michigan scientist who was not part of the study, said the research revealed that the regional links between carbon dioxide and El Nino are more complex than previously thought, and raised concern about how the earth will respond to more future warming.

As the world warms, the tropics could add to carbon to the atmosphere in the future instead of taking it out of the air and wildfire emissions are likely to get more severe, Overpeck said.

And some computer simulations say the frequency of El Nino will increase in the future with climate change, Denning said during a NASA press conference.

"In this sense, the 2015-16 El Nino is a glimpse of what is to come," Overpeck said in an email.