Ocean power in New Zealand speed. Because the tidal speed doubles, eight times more tidal power can be produced at spring tides than at neap tides. The entrance to Kaipara Harbour, one of the largest harbours in the world, is a channel to the Tasman Sea. It narrows to a width of , and is over deep in parts. On average, Kaipara tides rise and fall . At high tide, nearly 1000 square kilometres are flooded. Spring tidal flows reach 9 km/h (5 knots) in the entrance channel and move 1,990 million cubic metres per tidal movement or 7,960 million cubic meters daily. In 2011,
Issues relating to biofuels ecosystems including rainforest in South America. In forest ecosystems, these effects themselves will undermine the climate benefits of alternative fuels, in addition to representing a major threat to global biodiversity. Although biofuels are generally considered to improve net carbon output, biodiesel and other fuels do produce local air pollution, including nitrogen oxides, the principal cause of smog. Issues relating to biofuels There are various social, economic, environmental and technical issues with biofuel production and use, which have been discussed in the popular media and scientific journals. These include: the effect of moderating oil prices, the "food vs fuel" debate, poverty