A man in a suit plants a small tree.
By Matthew Prock.

Since the signing of the Paris Climate Accords in 2015, half of the world’s largest corporations have committed to reach “net-zero” emissions in the coming decades. Shell, Chevron and Volkswagen, three companies who have made this pledge, all have one thing in common: They are the top buyers of carbon offsets. Carbon offsets, or offset credits, are carbon-storing practices that polluters fund with the intention of compensating for their greenhouse gas emissions. These can be beneficial to the environment, but they are based on rough estimates of carbon sequestration and create a false notion of climate neutrality. Corporations and other groups should stop relying on offsets to go net zero.

The Walt Disney Company is one of many groups using forest-based offsets to try to nullify its pollutive practices. It has paid to plant more than 9 million trees and protect more than 1 million acres of existing forests in an effort to cancel out the millions of metric tons of carbon dioxide it releases from its entertainment parks, corporate campuses and cruise ships. Delta Air Lines emitted 14.3 million tons of greenhouse gasses in 2020. It has tried to make up for this pollution by preserving 780 square miles of forest in Indonesia and Cambodia. While these changes can have positive effects on the environment, their effectiveness as a carbon offset is questionable. Credits based on the planting of new trees, for instance, use an inaccurate estimate of the amount of carbon sequestered by a tree over the course of an unknown lifetime.

Forest-based offsets also generally overestimate the amount of emissions that they sequester. CarbonPlan, a nonprofit that analyzes offsetting schemes, studied the forest-based carbon credits used in California’s carbon cap-and-trade program. They found that 29% of offsets were over-credited, equivalent to 30 metric tons of carbon dioxide worth $410 million.

Quantifying the emissions absorbed by a forest is made even more difficult considering the fact that different species of trees and different types of forests can hold varying amounts of carbon. Local weather patterns, droughts and tree harvesting also affect the carbon capturing potential of a forest. There are also biases associated with what scientific data is used to make policy decisions about carbon offsets. A study led by the National Resources Defense Council found that the Canadian government uses data that drastically overestimates the amount of carbon dioxide that its forests contain by more than 80 million tons per year to indirectly support its logging industry. 

Even if the accounting of actual greenhouse gas sequestration was perfectly accurate, overplanting and over-preserving forests may not be a good idea. Overgrown forests are at a greater risk for wildfires, which will become more frequent as global temperatures continue to rise. Another issue is related to time horizons: A tree can absorb far less carbon in its lifespan than can be released into the atmosphere over that same period. 

Planting trees is not the only method companies use to compensate for their contributions to climate change. Another avenue is farm-based offsets, through which companies pay farmers to adopt carbon-storing agricultural practices such as no-till agriculture and perennial cropping. Like forest-based offsets, the actual quantity of greenhouse gas captured by these practices is difficult to determine. Soil carbon storage is also impermanent. For example, all of the sequestration gains made by no-till agriculture could be lost in an extreme weather event that disturbs the soil or if a farmer decides to plow his fields in the future. Perennial cropping and other climate friendly farming practices can also lower crop yields. This could incentivize farmers to expand farmlands by destroying nearby ecosystems, which is a highly emissive practice. 

The energy use of Michiganders and University of Michigan students in particular is tied to the purchase of carbon offsets. In 2020, the Michigan Department of Natural Resources created the Big Wild Forest Carbon Project, using 100,000 acres of state forest to create and sell carbon credits. DTE Energy, the electricity provider to Ann Arbor and the rest of southeastern Michigan, purchased the first decade of offsets from the program. With these credits, DTE says it will be net-zero by 2050. U-M students should be aware of the methods DTE uses to reduce its carbon footprint and be skeptical about any claims that it has gone carbon neutral. 

Supporters of carbon offsets will argue that despite the accounting issues associated with quantifying real carbon sequestration, the general idea is sound and we should strive to make offsets more effective. However, even if credits could be perfectly measured, they are still a license to pollute. They allow wealthy groups to avoid changing their practices and delay the large-scale cultural and behavioral changes required to truly combat the climate crisis. It would be far more productive for buyers of carbon credits to actually take steps toward reducing their own emissions, rather than relying on external groups to do it for them. 

Ethan Bittner is an Opinion Columnist from Santa Rosa, California. He writes about the global climate crisis and American culture. You can reach him at ebittner@umich.edu.