World's forests could hold 20 pct more carbon than previously thought

SAO PAULO - The world's forests could hold 20 per cent more carbon than previously thought, according to a study released on Tuesday.

If correct, that extra 125 billion tonnes of carbon could lead to an increase in the number of forest-based carbon credits set to be offered in carbon markets around the world.

Forests are considered sinks of carbon as they absorb carbon dioxide from the atmosphere, helping to reduce the concentration of the top heat-trapping gas.

Deforestation reduces the number of trees absorbing carbon dioxide and also releases carbon back into the atmosphere.

Scientists from the University of Edinburgh say they have developed a new 3D system to measure forests' carbon content that is more detailed and accurate than current methods.

For the study, the group analysed a specific forested area in Costa Rica and compared resulting data with previous calculations of carbon stocks.

Most projects that generate carbon credits by reducing emissions from deforestation (REDD) use satellite images associated with estimates of carbon content which vary depending on the type of forest.

The system used by the Edinburgh scientists is based on 3D data extracted from airborne laser scanning. "Satellite data cannot provide information on the vertical dimension of the forest, such as canopy height and layering, which are crucial to accurate measurement of the carbon," said team leader Iain Woodhouse.

Satellite-collected data from existing studies found the area in Costa Rica contained between 14.4 and 16.3 million tonnes of carbon, while the new method estimated the same area to hold 19.8 million tonnes.

But the new system could be more expensive for REDD project developers.

Forest-based offsets are expected to be included in a global climate deal currently being negotiated.