Appalachian mountains
Mountain-top coal mining in Appalachians has "staggering" environmental impact (Reuters)

An area the size of Washington DC would need to be mined every 81 days in order to meet demand for coal in the US through surface mining.

A year's supply of coal means 310 sq m of the Central Appalachians needs to be mined to meet demand, equivalent to 10 city blocks every hour.

Researchers at Duke University, Kent State University and the Cary Institute for Ecosystem Studies have for the first time looked at the "environment price tag" of mountain-top coal removal.

Published in the journal PLoS One, they found mining to this extent would pollute 2,300km of Appalachian streams and cause the loss of carbon sequestration by trees and soils equivalent to the greenhouse gasses produced by 33,600 US single-family homes in a year.

William H Schlesinger, president of the Cary Institute of Ecosystem Studies in Millbrook, said: "This analysis shows that the extent of environmental impacts of surface mining practices is staggering, particularly in terms of the relatively small amount of coal that is produced. Tremendous environmental capital costs are being incurred for only modest energy gains."

Brian D Lutz, assistant professor of biogeochemistry at Kent State, said one problem regarding the environmental impacts of surface mining is that most studies look at the regional effect, rather than measuring the damage and comparing it to the economic benefits.

Two millennia before deficit erased

"This is a critical shortcoming since even the most severe impacts may be tolerated if we believe they are sufficiently limited in extent," he said.

Researchers used satellite images and historical coal production data to establish the total area of land mined and coal removed between 1985 and 2005.

In this time, 1.93bn tonnes across more than 2,000 sq km - enough to supply US coal demand for two years - had been mined.

They worked out the environmental costs by using previously reported assessments of damage.

"Given 11,500 tons of coal was produced for every hectare of land disturbed, we estimate 0.25cm of stream length was impaired and 193 grams of potential carbon sequestration was lost for every ton of coal extracted," said Emily S. Bernhardt, from Duke University.

"Based on the average carbon sequestration potential of formerly forested mine sites that have been reclaimed into predominantly grassland ecosystems, we calculate it would take around 5,000 years for any given hectare of reclaimed mine land to capture the same amount of carbon that is released when the coal extracted from it is burned for energy."

Lutz added: "Even on those rare former surface mines where forest regrowth is achieved, it would still take about 2,150 years for the carbon sequestration deficit to be erased."