The existing food system has failed and needs urgent reform, according to a UN expert who argues there should be a greater emphasis on local food production and an overhaul of trade policies that have led to overproduction in rich countries while obliging poor countries – which are often dependent on agriculture – to import food.

In his final report (pdf), Olivier De Schutter, the UN special rapporteur on the right to food, offers a detailed critique of an industrial system of agriculture that has boosted food production over the past 50 years, yet still leaves 842 million – 12% of the world's population – hungry.

"Measured against the requirement that they should contribute to the realisation of the right to food, the food systems we have inherited from the 20th century have failed," he told the UN human rights council. "Of course, significant progress has been achieved in boosting agricultural production. But this has hardly reduced the number of hungry people."

The right to food is defined as the right of every individual to have physical and economic access at all times to sufficient, adequate and culturally acceptable food that is produced and consumed sustainably, preserving access to food for future generations.

De Schutter, professor of law at the University of Louvain, Belgium, was appointed rapporteur in 2008, during a sharp rise in global food prices, and has had plenty of time to diagnose what ails food systems. A major culprit, he says, is the "green revolution", which boosted agricultural production through the use of high-yielding plant varieties, irrigation, mechanisation and subsidised fertilisers and pesticides. The flipside, however, was an extension of monocultures (wheat, maize, soybean), a loss of agrobiodiversity, accelerated soil erosion and pollution of fresh water from the overuse of chemical fertilisers.

A potentially devastating effect of industrial-scale agriculture has been the rise in greenhouse gas emissions, which represent 15% of total manmade emissions. Climate change will affect future agricultural productivity, he warns.

"Under a business as usual scenario, we can anticipate an average of 2% productivity decline over each of the coming decades, with yield changes in developing countries ranging from -27% to +9% for the key staple crops," says the report.

The increasing demand for meat is another area of concern. The UN's Food and Agriculture Organisation estimates that annual meat production would have to reach 470m tons to meet projected demand in 2050, an increase of about 200m tons from 2005-07.

"This is entirely unsustainable … Demand for meat diverts food away from poor people who are unable to afford anything but cereals … Continuing to feed cereals to growing numbers of livestock will aggravate poverty and environmental degradation," says De Schutter, who urges governments to discourage meat consumption where it has already reached levels that are more than enough to satisfy dietary needs. He is optimistic that public attitudes towards meat will change in rich countries, but less so about attitudes in emerging economies such as China, where eating meat is akin to a status symbol.

As an alternative to existing systems, De Schutter champions agroecology, a range of techniques including intercropping, the use of manure and food scraps as fertiliser and agroforestry (planting trees). This approach would not only be more environmentally friendly, but would contribute to more diverse diets and improve nutrition. Although easier to implement on smaller-sized farms, agroecology is also applicable to large farms.

Other measures to improve the system would be to abandon mandates for biofuels and cut down food waste in rich countries and post-harvest losses in poor countries.

Changes to support small-scale farmers in poor countries – access to land, support for local seed banks, storage connection to makers – must be accompanied by reform in rich countries, where the farming sector has become highly dependent on subsidies – $259bn in 2012. This has encouraged the expansion of the food processing industry thanks to cheap inputs and facilities such as silos and processing plants.

"Large agribusiness corporations have come to dominate increasingly globalised markets thanks to their ability to achieve economies of scale and because of various network effects … the dominant position of larger agribusiness corporations is such that these actors have acquired, in effect, a veto power in the political system."

De Schutter says he is not completely opposed to agribusiness as it is incredibly efficient in connecting consumers and producers far away from each other.

"It is not desirable to get rid of agribusiness," he says. "It is incredibly efficient, connecting far away consumers and producers, and many needs can only be satisfied by agribusiness. But we need alternative systems to serve different needs. There is an imbalance, as there has been a priority on large-scale farming and underinvestment in local food markets. It is more realistic to have different systems co-exist. Brazil shows you can have huge, efficient farms along exemplary family farms, but you do need high-level political commitment to small farms and a participatory tradition."

De Schutter sees possibilities for change. Rebuilding local food systems, for instance, would decentralise food systems, making them more flexible and creating links between cities and rural hinterlands. He cites urban agricultural initiatives in Montreal and Toronto, Canada, Durban, South Africa and Belo Horizonte, Brazil, where "family farmers" are encouraged to feed urban populations.

At the national level, governments should encourage investment in local food packaging and processing industries. Social protection schemes should be established, says De Schutter, offering a social safety net to protect vulnerable families from falling into poverty. Globally, meanwhile, states should limit excessive reliance on international trade and build capacity to produce the food needed to meet consumption needs, with an emphasis on small-scale farmers.

"The expansion of trade has resulted in the luxury tastes of the richest parts of the world being allowed to compete against the satisfaction of the basic needs of the poor," says De Schutter.

As for the power of agribusiness corporations, states should use competition law to check the abuse of power. "This requires having in place competition regimes sensitive to excessive buying power in the agrifood sector, and devising competition authorities with mechanisms that allow for affected suppliers to bring complaints without fear or reprisal by dominant buyers."