Carbon storage in land ecosystems, especially forests, has offset around 17% of annual U.S. fossil fuel emissions of greenhouse gases over the past several decades, but this carbon “sink” may not be sustainable.

This finding is from chapter 27 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: Evaluation of literature by Coordinating Lead Authors

Description of evidence base: Underlying data come primarily from U.S. Forest Service Forest Inventory and Analysis (FIA) plots, supplemented by additional ecological data collection efforts. Modeling conclusions come from peer-reviewed literature. All references are in Section 2 of the Mitigation Chapter. Studies have shown that there is a large land-use carbon sink in the United States.8e71f863-8c83-4786-900c-ad8c8c252b30 385bda86-7b42-4264-9673-280ac0091528 4c53dfcf-e3e2-47e0-a356-369324e49cd5 Many publications attribute this sink to forest re-growth, and the sink is projected to decline as a result of forest aginge7804fe4-5cd0-4540-afde-621db767df51 0489f172-b2e0-4b90-aa40-7ba9993bd287 2f38407f-72d7-4ab2-a166-fac9069cec6c 1c5fc609-7a42-4983-ad95-92e3900eed41 and factors like drought, fire, and insect infestations0489f172-b2e0-4b90-aa40-7ba9993bd287 reducing the carbon sink of these regions.

New information and remaining uncertainties: FIA plots are measured extremely carefully over long time periods, but do not cover all U.S. forested land. Other U.S. land types must have carbon content estimated from other sources. Modeling relationships between growth and carbon content, and taking CO2 and climate change into account have large scientific uncertainties associated with them.

Assessment of confidence based on evidence: High. Evidence of past trends is based primarily on government data sources, but these also have to be augmented by other data and models in order to incorporate additional land-use types. Projecting future carbon content is consistent with published models, but these have intrinsic uncertainties associated with them.

References :

• SAP 2.2. The North American Carbon Budget and Implications for the Global Carbon Cycle (385bda86)
• Age structure and disturbance legacy of North American forests (2f38407f)
• Carbon consequences of forest disturbance and recovery across the conterminous United States (1c5fc609)
• Forest Carbon Management in the United States (4c53dfcf)
• U.S. Agriculture and Forestry Greenhouse Gas Inventory: 1990-2008. Technical Bulletin No. 1930. (8e71f863)
• Carbon changes in conterminous US forests associated with growth and major disturbances: 1992–2001 (e7804fe4)
• Attributing carbon changes in conterminous U.S. forests to disturbance and non-disturbance factors from 1901 to 2010 (0489f172)