SINGAPORE Across the globe an emerging El Nino weather pattern threatens to cause droughts and floods and trigger a spike in planet-warming greenhouse gas emissions from burning forests.
El Nino is a warming of tropical Pacific waters that affects wind circulation patterns. Its effects on the global climate vary from one event to the next.
Trying to predict how El Nino will be affected by global warming is a major challenge, scientists say, although data shows El Ninos have become more frequent and more intense over the past three decades. The last event was in 2006.
"I don't think there are any studies that are saying El Nino will become less severe but there is disagreement among the climate models on whether they will become more severe or stay steady," said Matthew England of the Climate Change Research Center in Sydney.
Getting the forecasting right is crucial for farmers in planning their crops, and even for the oil industry in assessing storm risks in the Gulf of Mexico.
"Certainly we know from past climates that El Nino intensity has varied. As climate changes, we know that the intensity of El Nino can wax and wane over long time scales," he said.
Australia's Bureau of Meteorology said last week an El Nino was almost certain this year and the signs point to one already well underway. A formal declaration could be within days.
(For more details see the bureau's website at: www.bom.gov.au/climate/enso/)
One of the biggest threats from El Nino comes from the release of vast amounts of greenhouse gases through the burning of dried out forests.
Scientists say there is very strong correlation between El Nino and drought in Southeast Asia, which has large areas of carbon-rich peat forests.
"People are waiting for appropriate conditions to get rid of the forests," said Pep Canadell of the Global Carbon Project in Canberra.
"So the drier the El Nino the more incentive there is for people to take advantage of those unique conditions," he said. Most of the burning occurs in Indonesia.
SPIKE IN TEMPERATURES
During the very intense El Nino of 1997/98, fires in Southeast Asia released between 2.9 billion 9.4 billion metric tons of CO2, blanketing the region in a choking haze. The smoke equated to between 15 and 40 percent of global fossil fuel emissions and is credited with causing a spike in global temperatures.
By comparison, average annual emissions from forest fires in Southeast Asia between 2000 and 2006 were 470 million metric tons of CO2, while average fossil fuel emissions for the same period in the region were 543 million metric tons of CO2, said Canadell.
Over the past two years, forest fire emissions have plunged because of wet weather.
"I think the next El Nino we have here in Southeast Asia is going to be a big one in terms of emissions," said Canadell, whose project issues annual reports on the planet's "carbon budget."
"The longer it takes for an El Nino to come, the bigger the emissions will be because the more people will be keen in burning because they have been waiting all this time."
The effects of the current El Nino, if confirmed, could already be apparent in the weakening of equatorial trade winds that normally blow strongly east to west and in the amount of cloud in the eastern Pacific.
"As El Nino is developing right now we should start to experience its impacts as we speak," said Harry Hendon, a senior climate scientist at the Bureau of Meteorology in Melbourne.
"Historically our biggest impacts are in the (southern) spring. But we start to see them as early as winter," he said.
SAME BUT DIFFERENT
Normally, warm ocean water is piled up in the Pacific around east Asia causing rain and moisture-laden winds that flow over parts of Australia.
But during El Nino, the warm waters migrate east toward South America, taking the wet weather, often causing floods in Colombia, Ecuador and elsewhere.
It's unclear how intense the next El Nino will be but Hendon said even weak El Ninos can have a dire impact on rainfall in Australia, depending on where the warm water pool was in Pacific.
"El Ninos that are peaking in the central Pacific have a bigger negative impact on rainfall on Australia than El Ninos that peak further east," said Hendon.
Complicating the picture, scientists now know there are at least two types of El Nino, one in which the warm waters pile up against the Pacific coast of equatorial South America, and the other in which warmest of the waters are in the central Pacific.
Scientists from the Georgia Institute of Technology in the United States released a study last week showing that periodic warming of the central Pacific was linked to an increase in Atlantic hurricanes, a finding that could change the way oil firms assess storm risks for operations in the Gulf of Mexico.
Previously, El Ninos in general were thought to suppress hurricane activity, but the latest research suggests this is only for episodes where the warmest waters are off the South America.
"The fundamental problem is we don't simulate El Nino very well with our existing climate models," said Hendon. "That makes it a real challenge to run your model for a future climate and see how El Nino will behave."
(Editing by Alex Richardson)