nutrient pollution, subsidized water usage, subsidy payments and assorted other problems. Positive externalities include self-reliance, entrepreneurship, respect for nature, and air quality. Organic methods differ from conventional methods in the impacts of their respective externalities, dependent on implementation and crop type. Overall land use is generally higher for organic methods, but organic methods generally use less energy in production. The analysis and comparison of externalities is complicated by whether the comparison is done using a per unit area measurement or per unit of production, and whether analysis is done on isolated plots or on farm units as a whole. Measurements of biodiversity are highly variable between studies, farms, and organism groups. "Birds, predatory insects, soil organisms and plants responded positively to organic farming, while non-predatory insects and pests did not. A 2005 review found that the positive effects of organic farming on abundance were prominent at the plot and field scales, but not for farms in matched landscapes." Other studies that have attempted to examine and compare conventional and organic systems of farming and have found that organic techniques reduce levels of biodiversity less than conventional systems do, and use less energy and produce less waste when calculated per unit area, although not when calculated per unit of output. "Farm comparisons show that actual (nitrate) leaching rates per hectare[/acre] are up to 57% lower on organic than on conventional fields. However, the leaching rates per unit of output were similar or slightly higher." "On a per-hectare[/-acre] scale, the CO2 emissions are 4060% lower in organic farming systems than in conventional ones, whereas on a per-unit output scale, the CO2 emissions tend to be higher in organic farming systems." It has been proposed that organic agriculture can reduce the level of some negative externalities from (conventional) agriculture. Whether the benefits are private, or public depends upon the division of property rights. Issues A 2003 to 2005 investigation by the Cranfield University for the Department for Environment, Food and Rural Affairs in the UK found that it is difficult to compare the Global warming potential, acidification and eutrophication emissions but "Organic production often results in increased burdens, from factors such as N leaching and N2O emissions", even though primary energy use was less for most organic products. N2O is always the largest global warming potential contributor except in tomatoes. However, "organic tomatoes always incur more burdens (except pesticide use)". Some emissions were