Carbon mismanagement in Brazil

To the Editor

Knowing the gaps in CO₂ inventories is fundamental for climate change science, as well as for global politics. The uncertainty of the emissions estimates is a great challenge for global greenhouse-gas (GHG) mitigation, as are emissions management strategies. Brazil missed its opportunity to lead by example¹ in the matter of mitigation. In most countries, CO₂ emissions mainly come from industrial sources, whereas in Brazil the majority (∼80%) originates from land use, land-use change and forestry. Brazil's national climate change policy defines a GHG emission reduction target of 36.1–38.9% by 2020, however, recently approved amendments to the Brazilian Forest Code (BFC) frustrate any attempts to protect and manage wetlands². BFC is now allowing the shrimp farming industry to convert 10–35% of all salt flats into ponds, which could hugely increase CO₂ emissions.

Estimates indicate that Brazilian salt flats cover ∼230,000 ha. Freshwater and brackish tidal wetlands occupy an additional ∼5,000,000 ha. Like salt flats, brackish wetlands are under a tidal regime but differ in interstitial salinity variation. Although these wetlands are biogeochemically different, they could be wrongly identified as suitable areas for conversion to shrimp ponds. Fifty thousand hectares have already been occupied by shrimp production^3,4, mainly on salt flats⁵, and the BFC is now allowing the occupancy of another 36,000 ha. Agribusiness stakeholders claimed before the Brazilian Parliament that shrimp farming had the potential to be expanded over ∼1,000,000 ha (ref. 6). This occupancy is actually only possible if brackish wetlands (∼550,000 ha) are converted for shrimp production.

Despite the magnitude and increasing growth rate of shrimp farming during the past decade (from 7,000 to 90,000 tonnes per year production), its CO₂ emissions — resulting from both land conversion and shrimp production — have not been included in Brazil's emission statistics⁷, thereby underestimating the country's share in the responsibility of climate change mitigation. If we consider only shrimp farms that have already been installed, that land conversion led to the emission of 0.012 gigatonnes of CO₂ per year, given that one hectare of wetland soil stores about 1,298 tonnes of CO₂ and that 75% of this sink is released immediately after clear cutting⁸. These land conversions correspond to 1.5% of all Brazilian marine wetlands, or only 0.03% of the national territory; however, they alone account for 1% of the total Brazilian yearly CO₂ emissions⁹. BFC's related uncertainties regarding wetland types could make these estimates escalate by a factor of eleven. This is important not only for meeting mitigation targets, but also for conservation.