Nature Geosci. doi:10.1038/ngeo284 (2008)

It is vital to know how much carbon is stored in Earth's Arctic soils, because much of it could be released as greenhouse gases as the planet warms.

Chien-Lu Ping at the University of Alaska Fairbanks in Palmer and his colleagues dug 117 one-metre-deep pits across the North American Arctic region to gather data on this pressing problem. They combined this with 22 existing datasets from shallower holes.

Carbon content varied markedly according to land type, and the team's measurements range from 3.4 to 55.1 kilograms of carbon per square metre. Their average of 34.8 kilograms per square metre is substantially higher than previous measurements of between 20 and 29 kilograms per square metre, and suggests that current estimates of the total carbon stored in Arctic soils are too low.