By Stuart Grudgings
ILHA GRANDE, Brazil, May 22 (Reuters) - No one could say they hadn’t seen it coming.
The sand dunes had been advancing for decades before, two years ago, they finally swallowed the houses of Raimundo do Nascimento and 12 other families in Ilha Grande, an island in the Parnaiba river delta in northeastern Brazil.
Standing on the 14-meter (46-feet)-high dune that now completely covers his old home, the 53-year-old Do Nascimento describes the landscape of his childhood -- cashew trees as far as he could see. Not a dune in sight.
"It is beautiful now, but beauty brings misery," he said. "The cause of this is natural, but it is man-made as well."
Experts blame deforestation and population increases for the huge dunes that are advancing by about 25 meters (82 feet) a year, threatening to wipe the town of 8,500 people off the map. But they and residents also blame stronger winds and drier weather in recent years.
"The wind has been getting stronger. It is the motor of this process," said Luiz Roberto del Poggetto, an oceanographer whose firm was contracted by the government to find ways to contain the dunes.
A bout of extreme weather has reignited a debate about how climate change is affecting Latin America’s largest country, home to most of the world’s biggest rain forest and one of the world’s bread baskets.
Unusually heavy rains in the north and northeast have made hundreds of thousands of people homeless and killed about 45. Meanwhile, southern Brazil has been hit by a series of droughts, devastating farmers and cutting by a third the flow of water over the famed Iguacu waterfalls.
President Luiz Inacio Lula da Silva has expressed concern.
"Brazil is feeling climate changes that are happening in the world, when there is a severe drought in a place that didn’t have them, when it rains in places where it didn’t used to," Lula said in a recent radio broadcast.
While the exact effect of climate change is hard to measure due to a lack of historical data, it appears to be a factor in the extreme droughts and floods of recent years.
"We are seeing the warming and we are seeing conditions in many parts of the country that appear to be associated," said Carlos Nobre, a senior climate scientist at Brazil’s National Institute of Space Research.
Southern states have suffered droughts in seven of the past 11 years and the first hurricane recorded in Brazil hit the southern coast in 2004. The Amazon area had its worst drought in decades in 2005.
Warming also plays a key role in models of a so-called "tipping point" in which drier weather and deforestation combine to turn much of the Amazon forest into a savanna and possibly cut the flow of rain to southern farming states.
Daniel Nepstad, a senior ecologist and Amazon specialist at the Gordon and Betty Moore Foundation in San Francisco, said about half of the forest was "teetering on the edge" of not having enough water to survive the more intense dry seasons.
The drying process, which raises the amount of destruction by fires, was on course to release about 20 billion tons of carbon into the atmosphere over the next two decades, he said, about twice the current annual total of global emissions.
"It’s just really strange the weather we are seeing," he said. "If you talk to indigenous tribes ... they describe in detail how the rain has changed."
CHANGE OF HEART
One study used in government planning estimates that the Amazon area will heat up by as much as 6-8 degrees Celsius (10.8-14.4 Fahrenheit) by 2100, resulting in a 20 percent reduction in rainfall.
Average temperatures in Brazil have risen 0.8 degrees Celsius (1.4 Fahrenheit) over the past 50 years.
"We are already not talking of change as something in the future, but about something that is going on," said Roberto Smeraldi, Amazon director for Friends of the Earth.
After years of reluctance, Brazil’s government has shown more willingness to discuss curbing its carbon emissions.
As well as agriculture, the hydro-power that provides 85 percent of Brazil’s energy will suffer as river levels fall.
Brazil, the fourth-biggest emitter of greenhouse gases due largely to Amazon deforestation, has said it is ready to adopt emissions targets and aims to be a key negotiator at talks in Copenhagen in December to agree on a new global climate treaty.
Parts of the south this year had their driest April since 1929, forcing more than 300 towns to declare a state of emergency. Crop losses in the three states of Santa Catarina, Rio Grande do Sul and Parana from this year’s drought are estimated at more than $1.5 billion.
"There’s a very good chance that the rains that nourish the grain belt depend upon the Amazon," said Nepstad.
FAT COWS, THIN COWS
Yet the exact effects of climate change remain hard to pinpoint. Another possible cause of the recent weather extremes is the so-called La Nina effect characterized by unusually cold temperatures in the Pacific Ocean.
Even in southern Parana state, among the worst hit, the causes of the dry spells of recent years remain uncertain. Elci Dalgalo, a corn, soy and wheat farmer, said most farmers believed they were a natural phenomenon.
"As my grandfather and father would say, it’s seven years of thin cows and seven years of fat cows. Now we have thin cows," he said.
In Ilha Grande, weather changes might be caused by warmer ocean temperatures. During the dry season that peaks in August, residents fight a losing battle to keep sand out of their hair, food and houses. Twenty-seven homes have been buried in the past four years, town officials said.
"In six years, the town will be finished," said Del Poggetto, the oceanographer.
Almost in the shadow of a towering dune, 38-year-old fisherman Valdecir Rodrigues de Souza said he and his family would have to flee the advancing sand within a year or two. It was an unlikely place to find a climate-change skeptic.
"Don’t listen to what they say -- this is natural," he said, standing in his garden with his three young children.
(Editing by Alan Elsner and Todd Benson)