The Problems with Carbon Offsets from Tree Planting

One of the most common types of carbon offsets on the market comes from tree planting projects. Many companies sell these offsets, and claim that they can be used to offset greenhouse gas emissions from other sources, such as air travel, automobiles, etc. While planting trees obviously does have environmental benefits, selling carbon offsets from these projects is problematic in a number of ways:

• Methodological challenges - there is much scientific uncertainty around the precise quantification of carbon sequestered in trees and soils. For example, recent studies have suggested that there is more carbon stored in the soil of many forest types than in the above-ground biomass (trees & other plants), and this soil carbon can be disturbed and released by harvesting and reforestation activities. Without an accurate understanding of the carbon inventory, it is difficult to quantify what the net carbon benefit of planting a tree is.

• Permanence issues - although a newly planted tree will remove carbon from the atmosphere while it is growing, a forest is never permanent and may one day succumb to disease (e.g. mountain pine beetle outbreaks), fire, or logging – releasing the carbon into the atmosphere once again. Planting trees is therefore at best a temporary solution. This fact makes issuing creates carbon offsets from forests very difficult, as without some kind of insurance scheme – i.e. issuing temporary credits based on ongoing monitoring of the forest health - it is impossible to assure that the offsets sold won’t become worthless at some point in the future (e.g. due to forest fire 75 years after planting).
  
  On the other hand, avoided emissions (due to renewable energy projects) or reduced emissions (due to energy efficiency projects) are, in essence, permanent, because they prevent carbon from entering the carbon cycle in the first place. Keeping the carbon sequestered in the ground in form of coal, oil or gas is a much better solution than burning it and then later trying to sequester it with trees.

• Lack of space - It is simply not possible to plant sufficient numbers of trees to deal with the increased carbon dioxide emissions that are expected over the next half century. For example, it has been estimated that to soak up just the United Kingdom’s annual greenhouse gas emissions, one would need to plant a new forest the size of Devon and Cornwall every year – and look after them in perpetuity.

• Forests as a source of carbon emissions – Recent evidence suggests that global warming itself is stressing ecosystems and turning forests and forest soils into failing forests and, in the long run, into net sources of CO2. Thus, if we don’t curb our use of fossil fuels, it won’t matter how many trees we plant because these forests will be overcome and die as climate the climate continues to warm.

• Lack of additionality (i.e. above and beyond business as usual) – many forestry offsets are from tree plantings that would – or should – have replaced logged forests anyway. It is therefore difficult to claim that such plantings can be used to offset emissions from elsewhere. 

• Monoculture plantations – Old growth forests are often replaced by tree farm plantations that are heavily managed (including with chemicals and fossil fuel-intensive machinery) and do not offer the same biodiversity benefits as natural forests.

• No root-cause solution - investment in forestry offsets does not contribute to reducing society’s dependence on fossil fuels, something that is ultimately needed to address climate change. Responding to climate change means fundamentally changing the way we produce and use energy. Since there are limited funds to invest in emissions reductions projects, the voluntary carbon market (i.e. purchasers of offsets) will have a larger impact by directing its scarce capital to energy-related projects.
  
  
  
  
  
  
  It is for these reasons that many environmentalists are opposed to the use of tree planting to mitigate climate change, and why this is expected to become a public relations issue for companies and other organizations that use these types of offsets in the future.
  
  
  Resources:
  
  Credit Check: A Comparative Evaluation of Tree-Planting and Fossil -Fuel Emission Reduction Offsets - David Suzuki Foundation
  
  SinksWatch