How big did you say your lawn was ?

Carl Bialik the Numbers Guy has a blog at the Wall Street Journal. He was intrigued (and sceptical) about a figure the New Yorker used - that there were 50,000 sq. miles of lawn in the USA (1 sq mile = 640 acres) roughly the size of NY State.

Environmentally the use of pesticides, fungicides, nematocides, weedkillers, fertilisers in residential areas is highly signficant because the greatest environmental pollution is on golf courses and lawns. USGS National Water Quality Assessment Program (NAWQA) indicate that the three insecticides most frequently detected in surface water (streams and rivers) are diazinon, chlorpyrifos, and carbaryl. These are heavily used in urban and suburban areas.(FAQ's)

This nice fat round figure of 50K sq. miles dates from 2005, from a study by Christina Milesi who worked for NASA. She tried a sideways approach by studying 80 hi-res photographs of 13 urban areas - she noted (unsurprisingly) the more road, car parks, the less turf.

So she derived a formula, and using a Census Bureau map of roads. NOAA hightime lights she came up with an area of between 49,000 square miles or 77,000 sq miles. She got hold of a better higher resolution dataset, from the National Geological survey and arrived at a figure 31% lower.

Meanwhile NY state had done a survey and came up with 5,400 sq. miles or 11% of the state.

The U.S. DOA Economic Research Service undertook a U.S. land use survey in 2002, "drawing on various sources" Most Americans, and thus most residential lawns, would likely fall within the “urban land” category, which is 2.6% of the country, or 94,000 square miles.

But how big is NY State ? Indeed how big is any state, in a recent article the Numbers Man had the size of Rhode Island (depending on the source) Census Bureau = 1,045 square miles + water area of 500 square miles. Rhode Island government Web site lists an area of 1,214 square miles, including 165 or 169 square miles of water, depending on where on Web site you look. Encyclopedia Britannica apparently splits the difference, listing a total area of 1,212 square miles — which would imply 167 square miles of water.

Estimate Guy resolved the problem quicker and at less cost than all this calculation - Quick back of the envelope calculation…90Mn. homeowners (ish) with 1/4 acre of lawn each (ish) is 35,156 sq miles.

Now huge bets are going to be placed on cleaning up the aerial environment by Goverments worldwide in the next year or two - Kyoto II will (allegedly) shift around mind boggling billions of tonnes of carbon and truckloads of dollars. certainly some carbon traders will become instantly very rich.

Can we have any faith in the accuracy of much of the data upon which decisions will be based ?

PS : The US Census Bureau said that from 1900 through 1980, the U.S. land area held steady at 3,618,770 square miles. In 1990, for reasons unstated , the Bureau included territorial waters, the Great Lakes and coastal waters. “As a result, the total area reported for coastal States has increased correspondingly,” the Census report dryly observed. Nationally, total area shot up to 3,787,319 square miles — a jump of 168,549 square miles or 4.5% .