finding 7.2 : reduced-forest-co2-uptake

U.S. forests and associated wood products currently absorb and store the equivalent of about 16% of all carbon dioxide (CO₂ ) emitted by fossil fuel burning in the U.S. each year. Climate change, combined with current societal trends in land use and forest management, is projected to reduce this rate of forest CO₂ uptake.

This finding is from chapter 7 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: Very High. There is very high confidence that under projected climate changes there is high risk (high risk = high probability and high consequence) that western forests in the United States will be affected increasingly by large and intense fires that occur more frequently.5ba92ba4-eb88-480e-91de-a442b293e649 1639ecca-a0ca-48f4-b64c-a447fe137284 517021ad-7515-4d23-8b25-735f52448514 391560e0-40c1-4f9d-b063-e87d18c87e02 b95e9226-076c-4eb5-9367-472499624084 This is based on the strong relationships between climate and forest response, shown observationally298cdb3f-64e7-4ac9-814c-f8deefbf964b and experimentally.e9b2f293-1699-4bee-99b7-0d2fd93d267d Expected responses will increase substantially to warming and also in conjunction with other changes such as an increase in the frequency and/or severity of drought and amplification of pest and pathogen impacts. Eastern forests are less likely to experience immediate increases in wildfire unless/until a point is reached at which warmer temperatures, concurrent with seasonal dry periods or more protracted drought, trigger wildfires.

Description of evidence base: The key message and supporting text summarizes extensive evidence documented in the TIR, “Effects of Climatic Variability and Change on Forest Ecosystems: A Comprehensive Science Synthesis for the U.S. Forest Sector.”78f2cbd8-d8f2-4d99-abbd-017bad4d52f1 Technical input reports (58) on a wide range of topics were also received and reviewed as part of the Federal Register Notice solicitation for public input. A recent study1c8d310f-ee58-4c1f-836b-c1fc613d198b has shown that forests are a big sink of CO2 nationally. However, the permanence of this carbon sink is contingent on forest disturbance rates, which are changing, and on economic conditions that may accelerate harvest of forest biomass.154cffb6-4cf1-4b1f-8fee-a910cfaed3a0 Market response can cause changes in the carbon source/sink dynamics through shifts in forest age,f53bd33b-97d5-4027-a30c-54fd714563ea 97be2553-2941-4e54-8a88-a2d9d6ca1434 land-use changes and urbanization that reduce forested areas,2545714a-f4ac-48f4-8c8f-b0954f3cfef6 forest type changes,e7ba5143-b62a-479e-872c-5b5538124c63 and bioenergy development changing forest management.2545714a-f4ac-48f4-8c8f-b0954f3cfef6 dd77d60a-0b9f-4a5f-bb8b-41bba86a5ddc cefd546d-c937-47a1-81b4-6583558a910f 0169e20a-8550-4435-8db2-b149a7d1d94d Additionally, publications have reported that fires can convert a forest into a shrubland or meadow,b95e9226-076c-4eb5-9367-472499624084 with frequent fires permanently reducing the carbon stock.1d17a757-d02f-4259-ae58-6e91ae9e9415 fd76d9bc-754a-4d3e-b9ff-641ed3be2648

New information and remaining uncertainties: That economic factors and societal choices will affect future carbon cycle of forests is known with certainty; the major uncertainties come from the future economic picture, accelerating disturbance rates, and societal responses to those dynamics.

Assessment of confidence based on evidence: Based on the evidence and uncertainties, confidence is high that climate change, combined with current societal trends regarding land use and forest management, is projected to reduce forest CO2 uptake in the U.S. The U.S. has already seen large-scale shifts in forest cover due to interactions between forestland use and agriculture (for example, between the onset of European settlement to the present). There are competing demands for how forestland is used today. The future role of U.S. forests in the carbon cycle will be affected by climate change through changes in disturbances (Key Message 1), growth rates, and harvest demands.

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