An accounting problem in the way some greenhouse gas emissions are calculated could critically hobble efforts to reduce them in coming years as nations move to combat global warming, scientists warn in a new report.

The accounting irregularity even gives the impression that clearing the world’s forests, which absorb and thereby diminish heat-trapping carbon dioxide, is good for the climate, the scientists write in an article published Friday in the journal Science.

The problem boils down to this: In emission calculations, all fuel derived from plants and other organic sources  including ethanol  is generally treated as if it has no effect on carbon dioxide in the atmosphere, even though though biofuels do emit carbon dioxide when burned.

This might make sense if the source of the fuel were, say, a crop of corn grown on barren land specifically for use as fuel, because the crop would have absorbed carbon dioxide as it grew, offsetting what it emits when ultimately burned.