by Nelson Harvey
Ask the average person what a carbon offset is, and they’ll probably mention planting a tree long before they say anything about installing solar panels or cleaning up smokestacks. Trees, after all, have been a symbol of the environmental movement since its inception, and nearly everyone knows that they convert carbon dioxide into oxygen. They must be great at offsetting carbon emissions too, right?
Perhaps not, according to a recent study by a group of researchers with Duke University’s “Free Air Carbon Enrichment” project. After subjecting a plot of trees to elevated levels of carbon dioxide for 10 years, the scientists found that the trees grew about 20 percent more biomass on average, but the bulk of that growth occurred only in trees which also had acccess to more water and nutrients. Since global warming is likely to bring increased drought in many places, and since plants in the wild must always compete for limited nutrients, these results cast doubt on the notion that planting more trees will effectively offset much of our carbon footprint.
As researcher Ram Oren told a reporter for the website “LiveScience,” “If water availability decreases at the same time that carbon dioxide increases, then we may not have a net gain in carbon sequestration.”
Thankfully, if further study confirms these results, it will not mean the disintegration of the global carbon market. Adam Stein noted on the Gristmill blog back in July that tree-planting projects make up just 6 of the 1,783 projects in the pipeline under the UN’s Clean Development Mechanism, the international program allowing polluters in rich countries to finance offsets in nations that are not signatories to the Kyoto Protocol.
But even though tree-plantings are just a fraction of the global market, they represent a signifincant portion of retail offsets sold to individual consumers. Stein works for TerraPass, which is among the voluntary offset providers that does not include tree-planting projects in its portfolio. However, in a 2006 guide to retail offets produced by the organization Clean Air-Cool Planet, three of the eight offset companies profiled featured forestry projects as a sizeable chunk of their offset efforts. These companies included The Carbon Neutral Company, Climate Care, and co2 Balance.
Many offset companies already seem a bit wary about tree-planting projects for a whole host of reasons, many of which Stein mentioned in his July post. Among the most significant: trees can take up to 40 years to grow to maturity and always run the risk of dying or being cut down. Given this latest evidence on their ability to absorb excess carbon, anyone shopping for offsets may want to forsake the mascot of environmentalism for a more effective solution.