Selling sequestration credits is shaky, for several reasons. 1. Carbon may only move from the lower solis layers to the top foot. 2. Carbon may not stay in the ground nearly as long (a century) as the soil credit is sold for. 3. The error bars for measurements or claims are very wide, and include zero. 4. Sampling is relatively costly, so samples from a few sampled fields are combined in a computer model to estimate savings for many more unsampled fields. 5. Other lesser issues.
World's Plants and Soils to Switch from Carbon Sink to Source by 2100 - 0415.rtf - Limits to other nutrients are important.
Maps of carbon storage on land. Upper map shows historical levels of storage (1860-69).
Lower map shows model projections of the change in storage by 2100 as a result of nitrogen and phosphorus limits, under a high emissions scenario (RCP8.5). Source: Wieder et al. (2015).
Pg = billion tons (GT). Fossil fuel emissions to date are 300-400 GT (Pg).
Change in land carbon storage projections from CMIP5 (Coupled Model Intercomparison Project Phase 5) models, under a high emissions scenario (RCP8.5). Coloured lines show average model projection for no nutrient constraints (black), limits to nitrogen (red), and limits to nitrogen and phosphorus (blue). Box plots on right-hand side show range in model results. Source: Wieder et al. (2015).
Section Map: Carbon Emissions