Belch of laughing gas could heat up our planet

HERE'S one less-than-funny warm-up act. The last ice age may have ended partly because of the release of vast quantities of laughing gas, or nitrous oxide. A similar release could be on the cards later this century, although we cannot predict how much Earth will warm as a result.

Europe warmed by 5 ?C about 14,500 years ago, towards the end of the last ice age, and ice cores show that this triggered a pulse of nitrous oxide. This sped up the warming process, as the gas has 310 times the warming potential of carbon dioxide.

According to Mirjam Pfeiffer of the Swiss Federal Institute of Technology in Lausanne and her colleagues, the nitrous oxide came from the plants that prospered as the area began to warm. The team reconstructed how the ecosystem changed at a Swiss lake, Gerzensee, during this time by identifying pollen buried in sediment. As temperatures rose, the area was overrun by a shrub called sea-buckthorn (Hippophae rhamnoides).

Sea-buckthorn uses nitrogen from the air to produce nutrients. Modelling suggests that its chemical tinkering released a lot of nitrous oxide, perhaps 1.6 milligrams of extra nitrous oxide for every square metre of land covered by the shrub, every year (Palaeogeography, Palaeoclimatology, Palaeoecology, DOI: 10.1016/j.palaeo.2012.06.015).

Something similar could happen this century as Arctic ice retreats. What's more, warmer Arctic peatlands belch out nitrous oxide.

"If we have climate change proceeding very quickly, the huge amounts of nitrogen stored in our ecosystem may be released as nitrous oxide," says Klaus Butterbach-Bahl of the Karlsruhe Institute of Technology in Germany.

However, we don't know how much this will affect temperatures, says S?nke Zaehle of the Max Planck Institute for Biogeochemistry in Jena, Germany.

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