Arctic's grazing animals help global warming on its way

COULD vegetation help to offset global warming? Not if grazing animals such as caribou and musk oxen are allowed to do their worst.

As global temperatures rise, the shrubby vegetation at high latitudes should grow more strongly, allowing it to act as a green lung to soak up carbon dioxide. To test the effect of grazing on these growth rates, Eric Post from Penn State University in University Park, Pennsylvania, placed 25 open-topped glass cones, each one 30 centimetres high, in 15 square kilometres of shrubland in West Greenland.

The glass sides act like a greenhouse, trapping warm air inside, mimicking the effects of global warming. Caribou and musk oxen were allowed to graze the shrubs through the open tops of 13 of the cones. The remainder were fenced off to keep the animals out.

Post found that over five years, shrubs such as dwarf birch and willow trees grew better inside the cones than outside, as expected. However, grazing reduced this increase in growth by a fifth (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0802421105). Post hasn't yet plugged his data into a climate simulation, but thinks previous models have overestimated the capacity of the Earth's vegetation to absorb CO2 by 10 per cent.