Counting the climate-warming carbon dioxide locked up in forests could offer a cheaper way to curb the greenhouse gas than by considering only emissions from industry and fossil fuels, according to a new study.
Factories, power plants and petroleum-powered vehicles are likely to emit some 500 billion tons of carbon dioxide into the atmosphere this century, according to the study released on Thursday in the journal Science.
By contrast, the world's forests hold some 2 trillion tons of carbon. As long as the forests stand, that huge amount of greenhouse gas stays out of the atmosphere, but if some of these woodlands are cleared for farming -- including biofuel crops like ethanol -- they start releasing carbon into the air, where it can add to the problem of climate change.
So even green fuels can have a carbon cost, said study co-author James Edmonds, an economist at the Energy Department's Pacific Northwest National Laboratory and the Joint Global Change Research Institute in Maryland.
Right now, the carbon stored in forests has no calculated economic value, Edmonds said in a telephone interview.
But if the carbon emissions from chopped-down forests are factored into the overall cost of capping atmospheric carbon this century, the price is much less than if only industrial and fossil fuel emissions are considered, Edmonds said.
The results in management of the landscape are dramatically different and starkly contrasted, he said.
To keep atmospheric carbon concentrations at 450 parts per million -- the level advised by the U.N. Intergovernmental Panel on Climate Change to avoid the worst impacts of global warming -- the model that factored in forest carbon had a carbon price of about $1,300 a ton by the year 2095.
The model that considered only industrial and fossil fuel emissions had a carbon price of $3,500 a ton by century's end.
Carbon dioxide concentration in the atmosphere is currently between 380 and 385 parts per million, compared with a pre-industrial level of about 280 parts per million.