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This article makes the point that shrub intrusion into tundra reduces albedo, the percentage of reflected light, but doesn’t report actual impact on ground temperature. Albedo itself is not a good indicator of waste heat. Much of the extra absorbed sun energy is used by the shrubs for photosynthesis and the fixing of carbon and thus is unavailable for heating the environment. I hope this detail was addressed in the field experiment with accurate ground and ambient-air temperature measurements. The effect of the albedo alone may not tell the whole story.

Bob Pettit
Corvallis, Ore.

Some experiments suggest that even though the shrubs sequester carbon, the soil beneath loses even more, resulting in a net loss of carbon .—S. Perkins