About 40 percent of the world's population, mainly in Africa and Asia, use wood, charcoal or coal to cook, warm and light their homes, according to a review published by The Lancet Respiratory Medicine journal.

Maputo - Beaming with pride as she stirs a steaming pot of spinach and nuts, Maria Douca is one of the first in Mozambique's capital to own an ethanol-fired stove, burning fuel made from locally grown cassava.

Betting that thousands of other city-dwellers will also switch from their charcoal stoves, a multi-national consortium plans to generate carbon credits to sell to greenhouse gas emitters on the other side of the planet.

Under the Cleanstar scheme led by Danish biotech giant Novozymes, Mozambican farmers sell surplus cassava that is converted to ethanol at a new facility near the central port city of Beira.

The fuel is then shipped to Maputo, where Cleanstar sells the stoves. They say they cannot keep up with demand. Some 200 stoves were sold in the first month and another 3,000 are on order.

Douca has already bought two stoves despite the $25 (about 200) price tag - easily a week's income for her family of eight.

Simple, clean and compact, the appliance designed by Swedish company Dometic looks rather like a camping stove but does not produce smoke. For the first time in her life she can cook inside.

“I had problems with my eyes when I was cooking on the ground. My eyes ran, I had asthma problems,” she told AFP.

About 85 percent of Mozambique's energy comes from wood and charcoal. It is a leading cause of respiratory illness, and studies have shown that primitive cooking stoves kill more people per year - about two million - than malaria.

Cleanstar hopes to capture a sizeable chunk of Maputo's $153 million a year charcoal business. Ethanol sells at roughly the same price as charcoal - which has doubled in the past three years.

Bank of America Merill Lynch has put $4 million into the project, which will generate carbon credits, based on the reduction in carbon dioxide emissions.

The credits can be sold to polluters under trading schemes in places such as the European Union or Australia.

“I have seen a dozen different cook stove projects that economically haven't made sense. This is the first one I've seen that is completely integrated,” the bank's carbon markets portfolio director, Abyd Karmali told AFP.

“From an environmental standpoint it is delivering a very large greenhouse gas emission reduction.”

A move by the European Union to accept new carbon credits only from the world's poorest countries after 2012 has made countries like Mozambique more attractive to investors.

If successful, its investors believe the Cleanstar model could be replicated across the region.

“The reason this is interesting is the potential to replicate it not only once but 10,000 times across Africa,” Novozymes president Steen Riisgaard told AFP.

“Every single link in the value chain should make good money for themselves or the whole thing will fall apart. Also a little money for us selling enzymes,” he added.

The company's enzymes help convert cassava chips into ethanol fuel at the Beira plant, the first of several planned facilities.

Initially hesitant to support the sale of cassava - a basic food for many - Mozambique's government now embraces the project.

“There is no contradiction between producing for food and producing for agro-industry. Our country is vast,” Agriculture Minister Jose Pacheco told AFP.

Despite its fertile soils and favourable climate, Mozambique uses less than one tenth of its arable land - the lowest land use in southern Africa.

Farming occupies 80 percent of the workforce, most cultivating just one hectare. Few farmers have access to seeds, fertilizers or modern equipment. Malnutrition is rife and the country is a net importer of staple foods.

On the face of it, everyone is a winner - the makers of the stoves and the ethanol, the family that uses the new gadget and the climate itself.

That would be some rare good news indeed for the environment, whose state is being debated at a UN conference in Rio de Janeiro this month. Culminating in a forum of world leaders on June 20-22, the meeting is the 20-year follow-up to the 1992 “Earth Summit” that declared war on climate-altering greenhouse gases.

Even so, some observers are circumspect.

“The developing world is littered with literally hundreds, perhaps thousands of attempts at improved stoves,” said Joseph Hanlon, an expert on Mozambican agriculture.

“They all work on a small scale but are never widely adopted. There are many reasons why changing cooking methods is difficult. Technofixes rarely work.”

Back in Maputo, Douca's family admit they still keep their old charcoal stove burning in the outside shed.

“We use this (new) stove a lot when we are making tea or boiling eggs, but for our main big dishes we use charcoal,” said Maria's son, Castigo.

Thanks to the new stove the family has reduced its coal consumption by half but he says charcoal is still best when you are grilling meat.

“It is a question of habit. We have always used charcoal.” - Sapa-AFP