Russell Beard finds out about a highly efficient closed-loop system known as 'aquaponics', where fish and vegetables grow symbiotically. This means produce and protein can be cultivated sustainably and profitably in cities. Founded by Will Allen, an ex-professional basketball player-turned-urban agriculturalist, Growing Power is an urban farm with a difference in Milwaukie, Wisconsin.
At their 0.8 hectare inner-city plot you will not only find vegetables and salad greens, but fish tanks holding 10,000 fish each whose waste is used to fertilise the plants. Growing Power's headquarters is said to be the most productive farm of its size in the US mid-west, and it trains hundreds of volunteers from around the world each year.
Inspired by this approach, a group of entrepreneurs have now set up their own commercial aquaponics farm in a nearby industrial wasteland. Sweet Water Organics sell their tilapia, perch and salad greens to local restaurants and shops, and are planning to expand the operation to produce six times more food than they currently do - using half as much energy.
Haiti's coral reefs once attracted divers from around the world, but now very little living coral remains - mainly due to severe over-fishing. Haiti is also the only country in the Caribbean that does not have marine protected areas.
California-based non-governmental organisation Reef Check is training young Haitian students to become 'eco divers' to survey Haiti's reefs, and become ambassadors for reef health. Before the programme started, virtually none of the students could swim - let alone dive - because of local superstitions surrounding water. The Reef Check team had to start the training from scratch, but the students are already making remarkable progress.
How it works: Thorium Reactor
This week's animation explains the thorium nuclear reactor. A number of research projects are currently exploring thorium as an alternative to traditional nuclear fuels. A traditional reactor generates energy by heating water using enriched uranium rods. The uranium's nuclear reactions heat the water into massively pressurised steam which is then used to turn a turbine, creating electricity.
Thorium reactors operate in a similar way, but the process is safer and easier to control, and the waste produced has a far shorter half-life, which means it loses its dangerous radioactivity much faster than traditional nuclear reactors.
The fast-growing city of Bhubaneswar in eastern India used to be dependent on hydroelectric power for 60 per cent of its energy needs, but after several years of low rainfall this fell to 30 per cent.
Suffering frequent power cuts, the city decided to take action, and in 2007 it adopted a policy of energy efficiency. Municipal buildings were converted to alternative energy sources, including the city hospital. Although the steps being taken by the city are modest, their combined impact is significant, and the hope is that other cities will be inspired to adopt clean, sustainable energy solutions.
Source: Al Jazeera