Senegal's capitol city Dakar sticks out into the Atlantic Ocean on a peninsula. It's at least a thousand miles to the Sahara desert yet the air today is so thick with sand that the tops of buildings disappear in a sandy haze.

It's the worst sand storm in a year and people here are worried that climate change will cause these events to be more common. Seasons are shifting across the region. In Senegal the rainy season used to start in July or August but now it doesn't start until September. Decreased rain - along with over grazing of land - is causing an increase in deserts across the Sahel. Roughly 40 per cent of Africa is now affected by desertification and according to the UN, two-thirds of Africa's arable land could be lost by 2025 if this trend continues.

Senegal is one of 11 countries in the Sahel region of Africa looking towards the same solution to the desertification problem: The Great Green Wall. The goal of the project is to plant a wall of trees, 4,300 miles long and 9 miles wide, across the African continent, from Senegal to Djibouti. African leaders hope the trees will trap the sands of the Sahara and halt the advance of the desert.

Papa Sarr is Technical Director for the Great Green Wall in Senegal: "We are convinced that once we start to plant the wall of trees dust will decrease in Dakar," he says.

Sarr sits in the passenger seat of a four-wheel drive on his way to Widou, a village he hopes will serve as a model for the Great Green Wall in Senegal. The paved roads of Dakar give way to red sand paths of the Shahel; a dry savanna transition zone between the equatorial jungles in the south and the Sahara to the north. Black and white goats meander in front of the truck and flat-topped acacia trees dot the sandy landscape. They are virtually the only vegetation in a region where the dry season can last up to 10 months.

Four hours northwest of Dakar, the village of Widou sits next to one section of Senegal's Great Green Wall. The acacia trees here are just four years old, waist high and thorny. The trees are surrounded by a firewall and a metal fence to keep out tree-eating goats. All of the trees were chosen carefully. Sarr says, "When we design a parcel we look at the local trees and see what can best grow there, we try to copy Nature."

Two million trees are planted in Senegal each year; but all of them must be planted during the short rainy season. Labourers plant acacia saplings in the sand along with animal manure for fertiliser. Sarr points to a three feet tall tree. "This one is Acacia nilotica. It produces Arabic gum used in local medicine and a fruit that can be eaten by animals."

For the project to succeed, it was crucial to plant trees that would also provide benefits for people living here. The government has ambitious plans for planting more trees but the Great Green Wall is also a development project, aimed at helping rural people.

In the Senegalese Sahel the dominant ethnic group is the Peuhl. Tall and lean, they wear long flowing robes of emerald green and sapphire blue. They look like jewels against the rust coloured sand and brown dry grass. The women have blue tattoos on their chins and wear heavy earrings that stretch their earlobes.

Traditionally nomadic, the Peuhl are now helping tend to the trees and planting gardens. One day a week women in the area volunteer to help care for gardens full of carrots, cabbages, tomatoes and even watermelon. Guncier Yarati uses the side of her flipflop to mound the sandy soil around potato plants. "I like working here," she says. "I like working with my friends, we laugh and play while we work but what's really great is that we have more diverse vegetables. We eat the vegetables ourselves but sell them in the market too."

The closest market is about 30 miles away and before the gardens came along, it was a full day's trek in a horse-drawn cart to get fresh vegetables. Close by the potatoes, Nime Sumaso pours a jug of water over some carrots. She says, "when people came from Dakar and showed us that they could plant vegetables in their communities we saw that this would be a way to help women in our own community and so we knew the Great Green Wall project was important for us."

For the Peuhl, work is divided largely based on gender. So, while women mostly (and quickly) see the benefits of the project in their gardens, the men have a different perspective. A man's primary responsibility is to care for the family's large herds of goats and cows.

In the early morning white hump-backed cows with giant horns gather around water troughs. The Peuhl depend on their animals for subsistence, and livestock need a lot of water. Scientists say the trees of the Great Green Wall will improve rainfall and recharge the water table. So that's very welcome news for local herdsmen like Alfaca. "Planting trees is good for us," he says. "Those trees can bring water and water is our future. Water can solve our problem."

Everyone involved in the Great Green Wall agrees that the end goal is to help rural communities. But opinions vary on how the project will best manage to do that. African leaders envision the Great Green Wall as a literal wall of trees to keep back the desert. But scientists and development agencies see it more as a metaphorical 'wall,' a mosaic of different projects to alleviate poverty and improve degraded lands.

The Great Green Wall has received a total of 1.8 billion dollars from the World Bank and another 108 million dollars from the Global Environment Facility. Jean- Marc Sinnassamy is a programme officer with the Global Environment Facility. "We do not finance a tree planting initiative," he says, "it's more related to agriculture, rural development, food security and sustainable land management than planting trees."

The 11 countries involved with the project are committed to making progress but there are many challenges: abject poverty, shifting seasons and political instability are top among them. The entire region is in the middle of a food crisis. The United Nation's Food Program estimates that as many as 11 million people in the Sahel do not have enough to eat and Mali recently had a military coup.

Senegal is currently the furthest along with the Great Green Wall. They've planted roughly 50,000 acres of trees in addition to protecting existing trees. It's been successful so far in Senegal but not everyone believes it can work across the entire Sahel region.

Gray Tappan is a geographer with the United States Geological Survey. He says, "There's been a long history of one failure after another in external projects that come in and try to plant trees."

Tappan explains that there are many reasons these projects fail. Sometimes projects plant non-native species that can't survive in the dry climate, or local people don't support the project and allow their goats to eat the newly-planted trees.

In the village of Widou those concerns don't appear to be an issue but Tappan is skeptical as to whether the Widou model can be emulated through 4,300 miles of varying ecosystems and communities. He believes a better model can be found in Niger. Historically, farmers there removed any trees or bushes that sprouted up in their fields. But following a devastating drought in the 1980s farmers decided to allow the natural vegetation to grow and planted food crops around it. The result was a surplus of food and 12 million acres of trees, an area the size of Costa Rica.

Tappan has spent 30 years working in the region and admits he was shocked by the transformation: "In 2006 we did a big field trip across Niger and were just blown away by the vastness of this re-greening."

Scientists like Tappan believe that type of natural regeneration is much more likely to succeed than planting trees. But political leaders in Senegal are committed to their vision. Djibo Leyti Ka is the Minister of the Environment. He's in charge of the Great Green Wall project for the entire country. He says, "We have a lot of desert from Senegal to Djibouti. A wall of trees will stop the wind."

Ka dismisses critics who say it isn't practical. "They are crazy! The dust is coming. The sand is going to cover us all and we need to stop it. There are many many environmental projects in Senegal but this is the most important."

Back at the Great Green Wall near Widou, Papa Sarr stops to take in the work they've done so far. The waist high trees are just four years old but he expects big things from them.

"In 10 to 15 years this will be a forest. The trees will be big and this region will be completely transformed. We are already seeing animals come back that haven't been here for years. Mostly deer and many species of wild bird, even jackal," he says.

It's unclear if the newly elected president of Senegal, Macky Sall, will have as strong a commitment to the Great Green Wall as his predecessor Abdouley Wade. But for the people living here, tending their cows, watering the garden, and hoping the rains will come, the Great Green Wall holds great potential for positive change in Senegal and this region of Africa for generations to come.