Tree Planting as Carbon Offsets – Does Latitude Matter?

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It’s hard to argue against any program that advocates the replanting of forests, or the avoidance of destroying forests in the first place. We all know from grade school science that, through a process called photosynthesis, trees “breathe in” carbon dioxide and “exhale” oxygen, generating the energy they need to grow from the sun. It is almost a miracle of symbiosis that human beings do just the opposite – we breathe in oxygen and exhale carbon dioxide. Humans and trees have evolved together since the dawn of man. We are inextricably linked in the web of life on earth.

As it turns out, though, we humans do more than just breathe. We excavate the compressed and fossilized remains of early carbon life forms and burn it for fuel and for other purposes, we domesticate large numbers of animals for food who expel tremendous amounts of methane gas, a potent hydrocarbon, and we manufacture other carbon-based gasses – all of which throw the earth’s carbon balance out of whack, causing our planet to warm “unnaturally”.

Carbon offsets are one way to begin to reverse this process, with the intent of gradually bringing the carbon cycle back into balance. A reduced carbon emission on one end of the scale “offsets” a continued carbon emission on the other end of the scale. It’s a little crude, and will certainly take time, but I believe it is a step in the right direction.

But should trees be eligible for this carbon-offsetting scheme? And in particular, should planting new trees (called reforestation or afforestation) be accounted for to offset global carbon emissions?

A study published some time ago by the Lawrence Livermore National Laboratory suggests that trees may not make the best offsets, or at least planting trees in certain locations on the planet may not achieve the desired global cooling. See Climate Effects of Global Land Cover Change, published September 6, 2005.

In the study, researchers from Lawrence Livermore National Laboratory and the Carnegie Institution Department of Global Ecology show that a phenomenon known as “albedo” will actually result in the warming of the planet if more trees are planted in non-equatorial latitudes. Albedo is a term used to describe the reflection of light (and heat) from the sun. As it turns out, the difference between open grassland and forest cover is significant when taking albedo into account. This difference is magnified when snow-cover is considered. A snowy field reflects the sun’s heat while a forest absorbs the heat. Planting trees in mid to high latitudes may actually speed up global warming.

As stated by the report’s authors in its conclusion: “ In terms of the absolute potential for temperature modification by land cover change, there appears to be much more potential for heating by reforestation (planting new trees) than cooling by carbon storage. This has important policy implications, since incentives for tree plantations in non-equatorial regions may produce the opposite effect to that desired.” [Emphasis added].

A more recent study by the same authors published in the Proceedings of the National Academy of Sciences (April 2007) analyzes the impact of their earlier findings on three latitude bands: 20 degrees South to 20 degrees North (“Tropical”); 20 – 50 degrees in both Northern and Southern Hemispheres (“Temperate”) and 50 – 90 degrees in the Northern Hemisphere (“Boreal”). Their conclusions are consistent with the earlier study: “Latitude-specific deforestation experiments indicate that afforestation projects in the tropics would be clearly beneficial in mitigating global-scale warming, but would be counterproductive if implemented at high latitudes and would offer only marginal benefits in temperate regions.”

Why do the voluntary forestry standards currently under development ignore this important research? I have reviewed the four most prominent voluntary forestry standards (Climate, Community and Biodiversity Standard (CCBS), CarbonFix Standard (CFS), Plan Vivo Systems and Standard, and the Voluntary Carbon Standard (VCS) Agriculture, Forestry and Other Land Use (AFOLU)), as well as the California Climate Action Registry’s Forest Project Protocol and, as best as I can tell, none makes a distinction for latitude zones. Am I missing something?

More on this later.