For instance, if accounting is based on observed changes in carbon stock levels at the national level, the data will implicitly capture leakage between sources within the nation. Program-level actions are generally much less prone to leakage than narrow projects that are tightly circumscribed in space, time, and subject matter. For example, broad policy initiatives are more likely to influence deforestation rates than are direct actions of limited scope. Reduction of deforestation also captures many more complementary benefits, such as maintaining biodiversity, watersheds, and water cycling. On the other hand, quantifying the direct effects of a program is much more difficult than quantifying the direct effects of more discrete activities.
Optimal approaches are likely to include a mix of broad policy reforms and site-specific activities.
If accounting is to be adjusted for leakage, estimates would be needed of the magnitude of carbon benefits that are lost by each possible mechanism, and the carbon credit would have to be reduced accordingly. Because uncertainty in estimates of leakage magnitudes inevitably would be present, a further downward adjustment in carbon credit would be needed to assure a given certainty of achievement. Global climate benefits may be reduced not only through leakage but also by other forms of project failure. The adjustments that would be needed to accurately represent net GHG benefits are similar regardless of the origin of the failure. Because the probability of success varies greatly among global warming response options, an adjustment of credit for these probabilities would be necessary to assure valid comparisons of the benefits for global climate associated with each option.