Climate crisis: Colorado’s forests now emitting more carbon than they store each year

FORT COLLINS, Colo. — For centuries, Colorado’s forests have acted as giant carbon sponges, storing vast amounts of carbon dioxide and helping to regulate the climate. But new research reveals that these forests are now emitting slightly more carbon than they absorb each year. While they still hold an immense carbon stock—equivalent to the emissions from 1.3 billion vehicles—tree mortality from insect outbreaks and disease spread has tipped the balance, making them a net carbon source in recent years.

According to the detailed carbon accounting of forests from the Colorado State Forest Service, these vast woodland expanses still hold 1,558.1 million metric tons​ of carbon. However, they’re also losing about 3.2 million metric tons annually.

“People are looking to our natural ecosystems to mitigate climate change,” says lead author Tony Vorster, a research scientist with the Natural Resource Ecology Laboratory, in a statement. “We shouldn’t necessarily look to our forests to offset emissions because they’re currently a net carbon source across the state as a whole, and that trend is probably going to continue with ongoing droughts and wildfires.”

The problem stems largely from tree mortality. Widespread insect infestations, particularly bark beetles, have wreaked havoc across Colorado’s forests. These tiny beetles have affected over 20% of the state’s forests since 2000, leaving behind millions of acres of standing and fallen dead wood. Adding to this assault, decades of fire suppression have created unnaturally dense forests more susceptible to catastrophic wildfires. Climate change and drought have further stressed these woodland ecosystems.

Western Colorado’s spruce-fir forests, which typically store massive amounts of carbon, have been devastated by spruce beetle outbreaks. In the southwestern part of the state, these high-elevation forests lost more carbon than any other forest type. Meanwhile, the northwestern region saw significant carbon losses in lodgepole pine forests due to mountain pine beetle infestations.

In the eastern half of the state, ponderosa pine forests are actually managing to store more carbon than they release. These forests, adapted to frequent but less severe fires, have shown more resilience to current climate conditions. However, they face their own challenges from increasing wildfire risks and urban development pressures.

The study breaks down exactly where carbon is stored within Colorado’s forests. Most of the carbon, about 59%, resides in forest soils, while 20% is stored in living trees above ground. The remaining carbon is distributed among dead trees, roots, fallen wood, and forest floor material. Trees are approximately half carbon, absorbing carbon dioxide through photosynthesis and storing it as biomass in their trunks, branches, leaves, roots and soil.

Forest ownership also plays a crucial role. The U.S. Forest Service manages nearly half of Colorado’s forestland and oversees the largest share of forest carbon stocks. However, these federal lands are also experiencing the greatest carbon losses, accounting for 70% of the state’s total forest carbon emissions. Private lands, which make up about a quarter of the state’s forests, show smaller carbon losses, possibly due to different management approaches.

“While other reports have provided estimates for forest carbon, this report stands out as the first to focus solely on the state’s forest sector,” says co-author Ashley Prentice, a Colorado State Forest Service carbon specialist. “It delivers a detailed, in-depth analysis of how much carbon is stored, how it is changing, and the factors driving these changes.”

The report also examines how harvested wood products contribute to carbon storage. While lumber, furniture, and other wood products continue to store carbon, they represent less than 1% of the total forest carbon stock. However, these products offer an opportunity for long-term carbon storage while supporting local economies.

Insects and disease emerged as the dominant forces of change, affecting more forest area than wildfire, harvest, and weather combined during the study period. These disturbances were responsible for 85% of the total area impacted and 64% of disturbance-related carbon losses. Interestingly, undisturbed forests continued to sequester more carbon than they emitted, highlighting the importance of forest health in maintaining carbon storage.

Colorado has set ambitious greenhouse gas reduction goals: 50% below 2005 levels by 2030 and 90% by 2050. Understanding how forests factor into this equation is essential for meeting these targets.

“It’s natural for forests to cycle through times where they are carbon sinks and then carbon sources. We’re interested in long-term trends,” says Vorster.

Looking ahead, the situation may worsen before it improves. The devastating 2020 wildfire season, which saw three of the largest fires in state history, isn’t yet fully reflected in this data. As these burned areas are measured in coming years, they’ll likely push the carbon loss numbers even higher.

“We’re not going to plant our way out of this, but reforestation is a strategy that can be used to reduce the loss of forest and to mitigate some of these carbon losses,” adds Vorster.

He emphasizes that while carbon storage is important, forest managers must balance multiple priorities including wildlife habitat, recreation, economics, and wildfire risk. Sometimes, short-term carbon losses from activities like forest thinning might help retain more carbon long-term by reducing wildfire severity.

With this baseline data now available, Colorado forest managers can better understand how their decisions affect carbon storage. While the current trends are concerning, this inventory provides the foundation for developing more effective management strategies. Future updates will reveal whether these strategies can help restore these forests’ role as carbon sinks.