Climate-related disasters such as extreme heat and wildfires are now projected to turn these important carbon-absorbing sinks into net carbon emitters by 2070.
The lush Headwaters Forest Reserve, located six miles south of Eureka, California, near that state's northern border, is a tribute to conservation efforts to protect America's forests. Its 7,542 acres of public lands feature magnificent stands of old-growth redwood trees that provide nesting habitat for the marbled murrelet (a small Pacific seabird) and the northern spotted owl. Image: Bureau of Land Management, CC
Besides being a nurturing hub of intertwined ecosystems for some of the most important and unusual living creatures on the planet, healthy forests are also widely known for their ability to absorb excess carbon dioxide from the atmosphere.
According to the Department of Agriculture’s ongoing monitoring of the nation’s net carbon inventory, those forests currently absorb 10-15% of carbon emissions produced from all U.S. sources every year. For 2022, for example, that means those forests — including the trees and all other plant life thriving within them — absorbed 150 million metric tons of CO2 equivalent just in 2022 alone.
Those numbers work out to the equivalent belching of carbon emission from 40 coal-fired power plants.
Many have simply assumed that carbon absorption capability would just continue on forever. Or at least that it would continue functioning at that pace until renewable energy programs, the phase-out of those same high-polluting coal-fired power plants, and increased use of zero emissions vehicles such as conventional rechargeable EVs and hydrogen-powered ones, would kick in broadly enough so the forests could perhaps increase the percentage of much-lower net carbon emissions they draw in and store.
The new analysis just published by the USDA declares that, based on their analysis of what is happening to the forests, the vast forests in the country could transform into a “substantial source” of carbon emissions themselves by 2070.
This information comes from the latest edition of an ongoing analysis of forests’ ability to sequester carbon carried out by a special team within the USDA. That team tracks everything from the destruction of forest due to logging, mining, new housing developments and reallocated land use to make way for sprawling new agricultural fields; reduction of forest size because of wildfires; death of forest regions as they grow hotter and/or suffer from extreme drought; extreme weather events ranging from high-altitude atmospheric river events to tornadoes, more powerful hurricanes, and windstorms.
Characteristics differentiating the 2020 RPA Assessment scenarios. These characteristics are associated with the four underlying Representative Concentration Pathway (RCP) – Shared Socioeconomic Pathway (SSP) combinations used in the USDA Forests Report just published. Image: U.S. Department of Agriculture, Forest Service
These analyses are all made with respect to various scenarios prepared under the 2020 Resources Planning Act (RPA). Those scenarios represent a four-block matrix of projections, based on high or low warming happening in conjunction with low, moderate, to high growth. The USDA then add their projections of impacts of all other conditions, including the climate crisis, that exacerbates the impact of land use changes.
Among the major conclusions of this latest report are the following:
“Developed land use area is projected to continue expanding in the future — with increases ranging between 42 and 58 percent by 2070 across the four RPA scenarios, from an estimated 97.7 million acres in 2020.” Related to this, the report notes that, “Continued land use conversion, driven principally by increased developed land use, is ultimately projected to lead to net losses of forest land of between 1.9 and 3.7 percent by 2070 and net rangeland losses of between 1.0 and 2.3 percent.”
The increased growth of developed land use is also contributing to serious damage to existing forest ecosystems from nonnative invasive species spreading into these once-thriving “wild” areas. This will, according to the USDA, create significant “risks to biodiversity from land development include destruction of critical habitats, reduction in connectivity among habitats, and displacement or isolation of wildlife populations”.
The droughts which are also projected to make matters worse in all ecosystems will especially affect “forest and rangeland ecosystems of the RPA Rocky Mountain Region and the southern portion of the Pacific Coast Region”.
Wildfires due to drought, high temperatures, and winds are occurring in wider swaths, and more broadly in regions which had not previously suffered from serious flare-ups in the past. The report points out that the average annual areas destroyed by wildfires in the period from 2000 to 2017 was twice the rate of destruction during the period from 1984 to 1999, for example.
Those wildfires are also disproportionately destroying some of the most effective carbon absorbing of the various tree species in the United States.
“The largest increases in fire-killed tree volumes are projected to happen disproportionately in the Western United States among Douglas fir, ponderosa pine, and pinyon/juniper forests, as well as woodland hardwoods,” the report explains.
Rising sea levels due to glacial and other ice melting at the two poles, Greenland, and other locations are expected to cause rapid tree ecosystem collapse along the U.S. East and Southern Coastlines, with the rate of that accelerating by mid-century. Even now this is transforming what used to be healthy coastal forest ranges in those areas into saltwater marshes.
Rapid land use change in the North and South RPA region over the next few decades is expected to put significant stress on biodiversity in those areas, with formerly well-separated forests suffering the worst effects of it.
“Projections for the coming decades indicate that these regions are the most vulnerable to the stress of land use change in the form of land conversion to development, expansion of agricultural areas, and development of energy infrastructure and mining,” the report indicates.
Further, despite that “the Pacific Coast and Rocky Mountain Regions have expansive areas of Federal lands, their associated biodiversity is projected to be under high climate stress, in part due to their locations at high elevations,” the report goes on. So, despite good planning in advance by federal and regional governments to set aside large, protected areas in these regions, the climate crisis – which respects no such boundaries – will cause even more damage to come.
One surprising positive in the report is that water use per capita in the U.S. has been declining rapidly in recent years, even in areas with substantial population growth. The major factors in making that possible are an increased use of high-efficiency appliances, low-flow toilets, and restrictions on landscaping and other turf except for solutions which use far less water.
“Domestic water use decreased by 10 percent from 2005 to 2015 despite an 8-percent increase in population,” the report explains. “Per capita household withdrawals fell from 98 gallons per day in 2005 to 82 gallons per day in 2015. During the same period, surface freshwater withdrawals decreased in 64 percent of counties in the conterminous United States to about 322 billion gallons per day. Irrigation withdrawals fell by 7 percent, and thermoelectric withdrawals fell by 34 percent.”
While some of that may have been dictated by mandated decreases in water consumption in the presence of extreme drought conditions, the USDA experts maintain that much of this comes from the availability of lower water use solutions available to industry, agriculture, and the general public. It also points the way to policy decisions to encourage the development of such solution, so as to protect the important groundwater reserves which are necessary to support forests and other natural ecosystems adjacent to populated areas.
The report continues to explain in some detail that although the worst of what they are projecting is still decades ahead, U.S. forests nationwide are already rapidly declining in their ability to mitigate the increasing output of carbon emissions they used to absorb. That absorption rate is already plummeting, so that within just a decade or so these forests – even though still absorbing something – will have little impact on overall net emissions in the country.
The overall conclusion of the report, that America’s forests can no longer be counted on as a carbon sink to address even 10% of the regional carbon emission problem, needs to be taken seriously. While reforestation is essential, it can't stop the runaway catastrophic climate change that is now upon us.
The “Future of America's Forest and Rangelands: Forest Service 2020 Resources Planning Act Assessment” report which provided these findings, was published by the U.S. Department of Agriculture’s Forest Service in July 2023. It is, unlike many government documents, a formally referred and externally peer-reviewed document.